S PA R Cnewsletter n° 23

STRATOSPHERIC PROCESSES AND THEIR ROLE IN CLIMATEA Project of the World Climate Research Programme

July

2004

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ContentsIn Memory of James R. Holton, by D. Hartman ...............................................................................1The 25th Session of the JSC of the WCRP, by A. O'Neill and A. Ravishankara ..................2Comprehensive Summary on the Workshop on "Process-Oriented Validationof CCMs", by V. Eyring et al. ...............................................................................................5Report on the Assessment of Stratospheric Aerosol Properties: New Data Record, but no Trend, by L. Thomason and T. Peter ............................................12Report on Chapman Conference on Gravity Wave Processes and Parameterisation, by K. Hamilton ..................................................................................15Solar Variability and Climate: Selected Results from the SOLICE Projet, by J. Haigh et al. .............................................19Report on Critical Evaluation of mm-/submm-Wave Spectroscopic Datafor Atmospheric Observations, by Y. Kasai and T. Amano .............................................30Future Meetings .................................................................................................................32

In Memory of James Reed Holton(1938-2004)

J ames R. Holton,65, died on

March 3, 2004 inUniversity HospitalSeattle, Washing-ton. Jim had suf-fered a stroke andheart attack whiletaking his mid-dayrun at Husky Sta-

dium on February 24, 2004. He seemedin perfect health at the time. JamesR. Holton had been a professor in theDepartment of Atmospheric Sciences atthe University of Washington for 38 years. He was a highly respectedresearcher, member of the NationalAcademy of Sciences and the author of aleading textbook in dynamic Meteo-rology.

Jim Holton was a great friend and sup-porter of the SPARC Project. He led aNATO workshop on “Stratosphere-Troposphere Exchange”, which washeld in Cambridge, England, just priorto the first formal meeting of theSPARC SSG in September of 1993. Jimwas an outstanding teacher, a lucid and

engaging lecturer, and a formidableorganizer and promoter of SPARC-related research initiatives.

Jim Holton leaves a tremendous legacyin the scientists he helped to develop.He supervised 26 doctoral students,many of whom have gone on to leader-ship roles, particularly in SPARC-related fields. In addition, he workedwith about 20 postdoctoral visitors atthe University of Washington, most ofwhom have become scientific leaders,including the current Co-Chair of theSPARC SSG, Alan O’Neill.

Jim Holton was born in Spokane,Washington, and grew up in nearbyPullman, the site of Washington StateUniversity where his father studied di-seases of wheat and was director of aUSDA laboratory. J. Holton was seniorclass president and valedictorian of1956 at Pullman High School. He wentto Harvard College, where he received aB.S. degree in physics in 1960. While ajunior at Harvard, he met MargaretPickens, who later became his wife of40 years. They were married after Jim’s

second year as a graduate student atMIT. Jim worked with Professor JuleCharney at MIT and earned his Ph.D. in1964.

He received an offer of employmentfrom the University of Washington inhis home state, but he had also receivedan NSF postdoctoral fellowship. TheUniversity of Washington waited whilehe and Margaret enjoyed a year inStockholm, Sweden, where Jim visitedthe group of Bert Bolin. J. Holton tookup his assistant professor position inthe Department of AtmosphericSciences at the University ofWashington in 1965 and remainedthere, except for occasional sojournsaround the world, until his death.

His first work had to do with studyingfluid dynamics in the laboratory usingrotating tanks of salt water. He studiedthe role of viscous boundary layers intransient flow situations, which led toan important paper on the nocturnal jetalong the eastern slope of the Rockies.In 1968 he was author of four importantpapers on the Quasi-Biennial Oscillation

The 25th Session of the Joint Steering Committeeof the WCRP

Alan O’Neill(1) (alan@met.reading.ac.uk), and A.R. Ravishankara(2) (A.R.Ravishankara@noaa.gov),SPARC co-Chairs (on behalf of the SPARC SSG)

(1) - Data Assimilation Research Centre, Reading, UK(2) - NOAA-Aeronomy Laboratory, Boulder CO, USA

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of the tropical stratosphere, including apaper with R.S. Lindzen, which isregarded as giving the essential explana-tion of the QBO.

J. Holton continued to work on tropicaldynamics and wave interactions throughthe early 1970s. The first edition of histextbook was published in 1972. Hereceived the Meisinger Award of theAmerican Meteorological Society in1973. J. Holton visited the Departmentof Applied Math and TheoreticalPhysics at Cambridge University in1973-74 and his monograph on thedynamical meteorology of the strato-sphere and mesosphere was publishedin 1975. This monograph marked thebeginning of a long relationship with thequestions and characters that form theSPARC community. In 1976 he pu-blished papers describing two models ofthe stratosphere; a semi-spectral GCMand a simpler beta-plane model ofstratospheric vacillation cycles.

In the early 1980s, he did some obser-vational work showing the interactionbetween the QBO and the globalstratospheric circulation and its rela-tion to stratospheric wave driving. In1982 he was awarded the Second HalfCentury Award of the AMS, which waslater renamed the Charney Award. In1983, he began working on the role ofgravity waves in the stratosphere, andin 1984 wrote a review article on the

water vapour puzzle of the strato-sphere. Through the mid 1980s, heworked on dynamically based transportparameterisations for the stratosphere.In 1987, he published a co-authoredbook with David Andrews and ConwayLeovy entitled “Middle AtmosphereDynamics”.

The themes of atmospheric dynamics,stratosphere-troposphere constituentexchange, and gravity wave – meanflow interaction continued to benefitfrom Holton’s insight and leadership forthe remainder of his life. At the time ofhis death he was heavily engaged inplanning for the Aura Satellite launch,the use of HIRDLS data, and variousfield programmes designed to resolvequestions relating to the role of the tro-pical tropopause transition layer instratosphere-troposphere exchange ofenergy and constituents. Jim wasextremely productive until his suddendeparture. Both the fourth edition of“An Introduction to Dynamic Meteo-rology” and “The Encyclopedia ofAtmospheric Sciences”, which he co-edited with Judy Curry and John Pyle,appeared in print in 2004. The newedition of his classic text is updated andexpanded, and includes a CD withMatlab examples and exercises.

Jim Holton won virtually every awardavailable to an atmospheric scientist. In1994, he was named a member of the

US National Academy of Sciences. Hereceived an honorary doctorate from theStockholm University and an honoraryprofessorship from the University ofBuenos Aires in 1998. He was awardedthe Roger Revelle Medal of the AGU in2000 and the Rossby Research Medal ofthe AMS in 2001 – the highest awardsfor excellence in research given by thesetwo professional societies. He served asChairman of the Department ofAtmospheric Sciences at the Universityof Washington from 1997-2002.

Jim will be greatly missed by his wifeMargaret; sons Eric and Dennis;Daughter-in-law Gretchen; grandchil-dren Jake, Bailey and Noah; sistersJanet and Shirley; friends and col-leagues around the world. A memorialcelebration was held at the Universityof Washington on 3 April 2004. Hiscolleagues and students repeatedly tes-tified to the kindness, generosity andhumanity that accompanied both hisscientific excellence and his athleticprowess.

Memorial contributions may be sent tothe James Holton Building Fund at NewHope Farms, P.O. Box 89, GoldendaleWashington 98620, USA.

The 25th session of WCRP’s JointSteering Committee (JSC) was held

at the Headquarters of the RussianAcademy of Science, Moscow, from 1to 6 March 2004. It included a joint,one-day session with the ScientificCommittee of the IGBP. M.-L. Chanin,A. O’Neill and A.R. Ravishankaraattended on behalf of SPARC.

JSC sessions review progress in achiev-ing WCRP general aims with specialattention to the advances within thefour WCRP core projects – CliC, CLIVAR, GEWEX and SPARC. The JSC

the long-term goal of a seamless predic-tion problem, from weeks throughdecades to the projection of climatechange. A COPES Task Force is beingset up, supported by a Modelling Paneland by a Working Group onObservation and Assimilation of theClimate System. The WCRP projectshave been asked to formulate plans toparticipate in the COPES initiative, andto seek opportunities to work together.

In their presentation to the JSC ofdevelopments in SPARC, A. O’Neilland A.R. Ravishankara noted that

itself is keen to act as a sounding boardfor new ideas, and to offer advice andencouragement to the projects. Thisyear’s session was especially importantbecause WCRP is framing its specificobjectives for the coming decade, and isdeciding what changes in its pro-gramme and structure will be necessaryto achieve them. WCRP is placingrenewed emphasis on prediction, andis putting forward an initiative provi-sionally titled Coordinated Observationand Prediction of the Earth System(COPES), which will confront the scien-tific and technical challenges posed by

Dennis L. Hartmann

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SPARC has anticipated the emphasis ofCOPES by formulating all three of itsnew themes around the related issuesof our ability to attribute and to predictchanges in the climate system. Theysuggested that SPARC is the mainrepository in WCRP of expertise in thearea of chemistry-climate interactions,and A.R. Ravishankara presented fur-ther details of the rationale behind, andprogress with, SPARC’s theme onStratospheric Chemistry and ClimateInteractions. He mentioned, in particu-lar, that encouraging progress had beenmade in developing this theme as ajoint initiative with IGAC.

The SPARC presentation culminated insome specific questions to the JSC con-cerning SPARC’s evolution. Specifi-cally, should SPARC lead WCRP’sefforts within COPES on chemistry-climate interactions in both the strato-sphere and the troposphere? Moreover,the JSC was asked: should this majorresearch area evolve into a new WCRPproject linked to activities in IGBP, andif so on what timescale? The JSC wasunequivocal in their support for SPARCtaking a leading role on climate-chemistry interactions within WCRP,be it of stratospheric or troposphericimportance. The timescale for themetamorphosis of SPARC into a largerclimate-chemistry project will dependon the progress made within this themeof SPARC.

In the joint session between WCRP andIGBP, A.R. Ravishankara presented ashort summary of the progress made bythe joint IGAC-SPARC endeavour in thearea of climate-chemistry interactions.The two (of the three) co-chairs of IGACwere also present at this joint session.Clearly, the joint venture is the first ofits kind and has its origin in the initia-tives taken by M.-L. Chanin andM. Geller, the previous co-chairs ofSPARC. This joint venture was appre-ciated and encouraged by both IGBPand WCRP. It also became clear duringthe joint session, and the discussionsthereafter, that other close collabora-tions between WCRP and IGBP wouldnot emerge immediately. The mostlikely collaboration in the near futurewill be between the newly formedWCRP Working Group on SurfaceFluxes and the SOLAS project. It alsobecame clear that the collaborationshave to emerge from the “trenches” (i.e.from working scientists themselves),rather than from the “top”. In thefuture, as need arises in the area ofchemistry-climate interactions, SPARCis likely to closely interact with thefluxes group and SOLAS. Such colla-borations will surely arise when theneed is clear, as in the case of theIGAC-SPARC collaboration.

There were many compliments at theJSC to the approach - i.e., taking on“small” tasks and bringing them to

fruition - taken by SPARC in the past and now. Both the JSC and S. Solomon of IPCC commended themini-assessments of SPARC.

The JSC clearly saw the need for moreinteractions between projects andworking groups within WCRP. Fromthe perspective of SPARC, we need tostart attending the SSG meetings of theprojects and working groups, wheneverpossible. Further, we need to invitekey members of the other projects andworking groups to our SSG and GeneralAssembly.

Lastly, the officers of JSC and the pro-ject/working group co-chairs are tomeet more often than in the annual JSCmeetings. Such a meeting was held inlate 2003 in Geneva and another one isplanned for the fall 2004. This is anexcellent venue for bringing forth anyissues of specific concern to SPARC tothe attention of the JSC. We reallyshould take advantage of these more“informal” meetings to better commu-nicate the concerns and desires ofSPARC. Therefore, the SPARC commu-nity is hereby requested to bring to theattention of the co-chairs and the pro-ject office director any issues that theyfeel needs to be aired out. SPARC isours, WCRP is ours! Let us make itwork for us.

�

SPARC OFFICEDepartment of PhysicsUniversity of Toronto60 St George StreetToronto, Ontario, M5S 1A7Canada

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SPARC OfficeDepartment of Physics University of Toronto60 St George Street Toronto, Ontario, M5S 1A7Canada Tel: (1) 416-946-7543Fax: (1) 416-946-0513Email: sparc@atmosp.physics.utoronto.ca

Announcement

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Introduction

A number of Coupled Chemistry-Climate Models (CCMs) with detaileddescriptions of the stratosphere havebeen developed over the last 5-10 years.As they can address how climatechange, stratospheric ozone and UVradiation interact, now and in thefuture, a prime use of these models is toprovide O3 and UV predictions for theWMO/UNEP and IPCC assessments.Simulating the interaction betweenchemistry and climate is of particularimportance, because continuedincreases in greenhouse gases and aslow decrease in halogen loading areexpected, which both influence theabundance of stratospheric ozone.Because CCMs have been developedwith different levels of complexity,they produce a wide range of resultsconcerning the timing and extent ofozone layer recovery (WMO, 2003).The models are required to simulateextremely complex processes thatinclude quite subtle effects amid signi-ficant natural variability. In order fortheir results to be credible and treatedwith confidence, models must be care-fully validated against measurementsand other models. Recent validationwork has shown both the benefits thatcan be gained and the problems thatcan be encountered.

CCMs simulate a climate that at bestbears only a statistical relationship tothe real atmosphere, and so a compari-son of model results with measure-ments must be performed in a statisticalmanner in order to see how well na-tural variability is simulated. This isproblematic, because it appears to takemany decades of observations to definea robust stratospheric climatology,especially in the Arctic winter. Whiletropospheric climate models can be va-lidated, in part, by their ability to repro-duce the climate record over the 20th

century, the paucity of stratospheric cli-

mate data prior to the satellite era (post-1979) severely restricts such possibili-ties for model validation of strato-spheric ozone.

For these reasons, validation of CCMsneeds a process-oriented basis to com-plement the standard comparisons ofmodel and observed climatologies. Byfocussing on processes, models can bemore directly compared with measure-ments. Furthermore, natural variabilitybecomes an aid rather than an obstaclebecause it allows one to explore para-meter space and, thereby, more readilyidentify cause and effect relationshipswithin a model. An important exampleof this approach is the validation ofchemistry and transport processes inboth 2D and 3D models that is docu-mented in the NASA “Measurementsand Models II” Intercomparison (Parket al., 1999). In the context of strato-spheric General Circulation Models(GCMs) (i.e., those without chemistry),process-oriented validation representsthe level II tasks within the GCM-Reality Intercomparison Project forSPARC (GRIPS) (Pawson et al., 2000).A first attempt at process-oriented vali-dation of stratospheric CCMs is sum-marised in the 2002 WMO/UNEPAssessment (WMO, 2003) and dis-cussed in detail in Austin et al. (2003).

The development of a more compre-hensive approach to CCM validationwas the goal of a workshop held inNovember 2003 in Grainau, Germany.The workshop, titled “Process-orientedvalidation of coupled chemistry-climate models,” attracted approxi-mately 80 participants from Europe,USA, Canada, Japan and New Zealand.A primary goal of the workshop was tobuild upon the existing foundation ofvalidation efforts to achieve a more sys-tematic, long-term approach to CCMvalidation needs. A brief workshopreport was published in SPARCNewsletter No. 22 (Eyring et al., 2004).

Following this introduction, a more com-prehensive summary of the workshop ispresented. The summary includes aTable of Processes (Table 1), which was aprimary objective of the workshop. Thistable lists the core processes for strato-spheric CCMs within four main cate-gories: dynamics, stratospheric transport,radiation, and stratospheric chemistryand microphysics. Processes associatedwith the Upper Troposphere/LowerStratosphere (UTLS) are included underthese categories. For each process, thetable includes model diagnostics, vari-ables relevant for validation and sourcesof observational or other data that can beused for validation. The accompanyingtext discusses the importance of theselected processes to CCM validationand the utility of the selected diagnosticsin a validation study.

Several of the diagnostics have beenapplied before to a range of models, butmany have not. Various criteria wereused in selecting the primary diagnos-tics. The chosen diagnostics are asso-ciated with a well-understood modelprocess and have reliable measure-ments available for validation.

Dynamics

The stratosphere is strongly influencedby dynamical processes that CCMs mustbe able to reproduce correctly. Importantexamples are the forcing mechanismsand propagation of planetary-scaleRossby and (parameterised) gravitywaves, wave-mean-flow interaction(transfer of energy and momentum), andthe diabatic circulation. It is necessarythat CCMs are not only able to simulatethe climatological mean state of the stratosphere, including inter-hemispheric differences, inter-annualand intra-seasonal variability. As a firststep it must be shown that the basicdynamical properties of the underlyingGCMs, on which the CCMs are based, are

Comprehensive Summary on the Workshop on “Process-Oriented Validation

of Coupled Chemistry-Climate Models”

Veronika Eyring, DLR-Institut für Physik der Atmosphäre, Germany (Veronika.Eyring@dlr.de)Neil R.P. Harris, European Ozone Research Coordinating Unit, UK (Neil.Harris@ozone-sec.ch.cam.ac.uk)Markus Rex, Alfred-Wegener Institut-Potsdam, Germany (mrex@awi-potsdam.de)Theodore G. Shepherd, University of Toronto, Canada (tgs@atmosp.physics.utoronto.ca)David W. Fahey, NOAA Aeronomy Laboratory, Boulder, USA (fahey@al.noaa.gov).G. Amanatidis, J. Austin, M.P. Chipperfield, M. Dameris, P. Forster, A. Gettelman, H.F. Graf,T. Nagashima, P.A. Newman, M.J. Prather, J.A. Pyle, R.J. Salawitch, B.D. Santer, andD.W. Waugh

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Table 1. List of Core Processes to validate CCMs with a focus on their ability to model future ozone

Forcing and propagation of planetary waves

Stratospheric response to wave drag

QBO, QAO ***

Met. Analyses **

Satellite measurements of total ozone

Met. Analyses **, in situ and space-based observations, profile data

Met. analyses ** total drag inferredfrom diabatic heating calculation

Met. analyses **

Met. analyses **

Wave Frequency Analysis (WFA) Planetary Wave (PW) spectrum (variances & co-variances)

Hemispheric Ozone Variability Indices

Annual cycle of temperatures in tropics and extra-tropics

PW flux vs. polar temperature, lagged in time

Vortex definition, structure & occurrence of sudden/final warmings

Downward control integral, also scatter plot of PWD versus GWD

Persistence (e.g., leading EOFs), including Holton-Tan

Amplitude and phase (SAO) of horizontal winds and temperature

Temperature, Geopotential Height, horizontal winds High-frequency (daily) data

Total column Ozone over several years

Zonal monthly mean Temperature, residual streamfunction

Heat flux (v‘T‘) at 100 hPa (Jan/Feb)Temperature at 50 hPa (March) Zonal monthly means

Potential Vorticity, horizontal winds,Temperature, Area colder than PSC T, Vortex area/equiv. latitude Warming statistics High-frequency (daily) 3D fields

w* from model PWD, GWD, other drag zonal and monthly means

Geopotential Height, Temperature Multi-year time series (means, frequency spectra)

U and T, zonal and monthly means

Subtropical and polar mixing barriers

Meridional circulation

UTLS transport

Satellite and in situ (aircraft, balloons) chemical measurements andMet. analyses

Satellite and in situ measurements

Met analysis, satellite measurements

in situ measurements

Satellite measurements,Met. Analyses**

in situ and ground-based (polar only) and satellite data

Diabatic velocity inferred from radiative calculation

Balloon, aircraft

Met. Analyses**, Satellite measurements, ozonesondes

Diabatic velocity inferred from radiative calculation, ozonesondes

PDFs of long-lived tracers

Latitudinal gradients of long-lived tracers

Correlations of long-lived tracers

Phase and amplitude of subtropical CO2 or H2O annual cycle in lowerstratosphere (tape recorder)

Annual cycle of streamer frequency

Mean age

Correlation of interannual anomalies of total O3 and PW flux

Vertical propagation of tracer isopleths

Diabatic velocity, TEM streamfunction

Vertical gradients of, and correlationsbetween, chemical species in the extratropical UTLS

Relation between meteorologicalindices (e.g. tropopause height) and total ozone

Diabatic velocity, vertical O3 profiles in tropical tropopause layer (TTL)

N2O, CH4, F11, etc.; PV

CO2 or H2O

Daily PV (maybe long-lived tracers)

Conserved tracer with linearly increasing concentration, SF6 or CO2;

Total O3 and heat flux at 100 hPa, zonal and monthly means

H2O or CO2 or idealised annually repeating tracer (tropics), CH4 or N2O (polar)

Diabatic velocity, residual velocities

CO2, SF6, H2O, CO, O3, HCl

Daily winds, temperature, Z, total O3

Diabatic velocity, vertical O3 profiles

Solar UV-vis photolysis in stratosphere

Heating rates

Radiative heating

Transient response of global average temperature

Direct flux measurements (balloon, ER-2)

Inferred photolysis rates (ER-2)

Use sophisticated reference radiationmodels for comparison (Line by line)NLTE, Discrete-Ordinate scattering etc.

Assimilated fields derived from satelliteand sonde data, Meteorological analysis

SSU/MSU satellite time series

Radiative Transfer of 260-800 nm solar flux; Photolysis rates comparison up to 95°solar zenith angle including clouds

Comparison of thermal and solar heating rates in offline runs employingcolumn version of CCM radiation codes

Global average of temperature profile

Long-term globally averaged transienttemperature changes

Actinic flux (direct & scatter) Photolysis rates of O3 and NO2 at local noon Pressure, Ozone, stratospheric aerosols Tropospheric clouds, aerosols and Ozone

Heating rates and irradiances from CCMradiation code, with a prescribed and standardised set of input atmospheric profiles

Annually averaged global trace-gas and clouds fields, temperature

Changes in Ozone, water vapour & high clouds, greenhouse gases,Hydrofluorocarbons, aerosols etc.

Stratospheric Transport Coordination: Markus Rex and Darryn Waugh

Overall Coordination Veronika Eyring, Neil Harris and Ted Shepherd Process Diagnostic* Variables DataDynamics Coordination: Martin Dameris and Paul Newman

Radiation Coordination: Piers Forster and Steven Pawson

Photochemical mechanisms and short timescale chemicalprocesses

Long timescale chemicalprocesses

Summer processes

HOx: balloon, shuttle, A/C NOx: satellite, shuttle, balloon, A/C ClOx: satellite, shuttle, balloon, A/C BrOx: A/C

Satellite measurements of reservoirsand precursors

Satellite measurements of total Ozone

Offline box model comparisons of fastchemistry (of order one week or less)

Comparison of abundance of reservoirsand radical precursors

Tracer-tracer relations

Ozone changes in polar regions

Ozone changes in mid-latitude regions

Full chemical constituents (O3 loss due to Ox, HOx, NOx, ClOx, BrOx, J values)

Instantaneous output of all chemical constituents and temperature (one per month)

O3, NOy, CH4, H2O, N2O

Total Ozone, full chemical constituents, temperature

Stratospheric Chemistry & Microphysics Coordination: Martyn Chipperfield and Ross Salawitch

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reproduced. The analyses carried outduring the first phase of the SPARC-GRIPS project (Pawson et al., 2000) pro-vide a solid basis for the evaluation ofCCMs. The analyses compared the verti-cal and latitudinal structures of the long-term zonal-mean temperature derivedfrom observations and CCM simulations.Additionally, time series of monthlymean temperatures at distinct altitudesand latitudes help to identify and quan-tify overall model uncertainties.

Forcing and propagation of planetarywaves. To determine the properties ofthe generation of planetary waves, theirpropagation through the stratosphere andtheir role in the momentum budget of thestratosphere, i.e. the stratosphericresponse to planetary wave drag (PWD),an analysis of stationary planetary wavepatterns (up to zonal wavenumber 8) atdifferent altitudes between the free tro-posphere and the upper model layers isrequired. This diagnostic can be aug-mented by calculations of EmpiricalOrthogonal Functions (EOFs) and ofrefractive index. Supplementary to thestandard energy spectrum analysis,investigation of transient wave behaviour is necessary. Here, aWavenumber-Frequency Analysis (WFA)can help to resolve transient waves atdistinct wavenumbers into standing andeastward and westward travelling wavesat different frequencies (Hayashi, 1982).The WFA can be performed by usingpower-, co-, and quadrature spectra ofthe time spectral analysis methods, suchas the maximum entropy method, thedirect Fourier transform method or thelag correlation method. An example isdisplayed in Figure 1 (p. I). In order todetermine the amplitudes and phases ofthe zonal quasi stationary planetarywaves in the lower stratosphere, totalozone fields can be analysed by means ofspectral statistical methods. Here, thetotal ozone column is considered as a

conservative tracer to illuminate the vari-ability of wave structures in the lowerstratosphere. To derive the wave para-meters from the ozone distribution, thespectral statistical technique HarmonicAnalysis can be applied to each latitudewhich corresponds to an approximatedeconvolution of the power spectrum.The spectral properties can further beused to gain two hemispheric OzoneVariability Indices, which are defined asthe hemispheric mean of the zonalamplitude of the planetary waves num-ber 1 and 2.

Stratospheric response to wave drag.Correlations of Eliassen-Palm fluxes(i.e., vertical and meridional heat andmomentum fluxes) with dynamical andchemical fields (e.g., temperature, windspeed, ozone) and parameters (e.g., sizeand persistence of the polar vortex, PSCpotential) are necessary to investigatethe stratospheric response to wave dragand its consequences for chemical andphysical processes in CCMs (Newmanet al., 2001; Austin et al., 2003).

Moreover, a check of the ability ofCCMs to reproduce correctly the sea-sonality of the Brewer-Dobson circula-tion is needed. This can be done bycalculations of cross sections of theresidual circulation mass streamfunc-tion (latitude vs. height), which arebased on re-analyses (e.g., NCEP, ERA-40) and corresponding results derivedfrom CCMs. Derived diagnostic proper-ties, such as the relative roles of PWDand gravity wave drag (GWD) in polardownwelling, and seasonally depen-dent changes of low frequency be-haviour of stratospheric chemistry (e.g.,ozone loss in spring, absorbingaerosols) in coupled vs. uncoupledmodels must be checked.

Quasi-Biennual Oscillation (QBO),Semi-Annual Oscillation (SAO). It isalso important to validate the ability of

CCMs to reproduce key oscillations inthe stratosphere. One such oscillationis the semi-annual oscillation (SAO) ofequatorial zonal winds at thestratopause. All CCMs simulate this tosome extent, but the realism of themodels’ SAOs varies considerably.CCMs are now just beginning to simu-late the quasi-biennial oscillation(QBO), usually through the inclusion ofenhanced GWD. It will be important toconfirm that the models are obtaining aQBO for the right reasons, and that theextratropics responds in the correctmanner.

Stratospheric Transport

Transport in the stratosphere involvesboth meridional overturning (the resi-dual circulation) and mixing, whichtogether represent the Brewer-Dobsoncirculation. The most important aspectsare the vertical mean motion (diabaticvelocity) and the horizontal mixing. Thehorizontal mixing is highly inhomoge-neous, with transport barriers in the sub-tropics and at the edge of the wintertimepolar vortex; mixing is most intense inthe wintertime “surf zone” and isextremely weak in the summertimeextratropics. Accurate representation ofthis structure in CCMs is important forthe ozone distribution itself, as well asfor the distribution of chemical familiesthat affect ozone chemistry (NOy, Cly,H2O, CH4). Within both the tropics andthe polar vortex, the key physical quanti-ties to represent are the degree of isola-tion and the diabatic ascent or descent,respectively.

It is useful to distinguish between trans-port in the stratospheric “overworld” andin the UTLS. In the stratospheric over-world, there is a reasonably good under-standing of the relevant processes and ofhow to quantify them. In contrast, the

Polar processes in winter /spring

Denitrification & Dehydration

Stratospheric Aerosols

Aerosols & Cloud Microphysics

Satellite and aircraft measurements

Chemical Ozone loss diagnosed fromfrequent Ozone profiles in the vortexover several years Met. Analyses **

Satellite measurements of HNO3, H2O, CH4A/C obs. of NOy, H2O, CH4, N2O. PSC size distributions

Satellite and in situ measurements ofaerosols; aerosol climatologies

Aircraft and satellite measurements;process/cloud-resolving models

Partitioning of species within the families

Chemical Ozone Loss versus PSC activity

NOy vs. Tracer

H2O +2 CH4

Sulfuric acid size distribution; aerosol optical extinction

Cirrus cloud frequency of occurrence;H2O distribution

Species from families (ClOx, NOx, HOx,BrOx, Cly, NOy, BrOy) temperature, PV fromwind fields

O3, passive O3 tracer, O3 prod./loss rate, PVfrom wind fields, temperature

NOy, HNO3, N2O, CH4, etc.

H2O particle-flux rates added to daily polarchem. Instantaneous output, CH4

Sulfuric acid mass, particle number conc.,water vapour, Temperature

Ice water content, water vapour,Temperature, aerosol size distribution

* in addition to traditional model validation (climatological means, inter-annual variations)** due to uncertainties use several analyses, not one*** inter-comparison currently not possible because process not included in most CCMs

Advisory Group John Austin, David Fahey, Andrew Gettelman, Tatsuya Nagashima and Ben Santer

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Diabatic ascent or descent has twoaspects. First, a model must have the cor-rect vertical residual velocity (or, equiva-lently, diabatic heating or cooling rates).This is controlled by the wave drag in thestratosphere and above. There are nodirect measurements of these quantities,and, hence, they must be inferred fromradiative calculations based on observedor assimilated temperatures and radia-tively active species. This introducessome uncertainties in the comparison.The second aspect is the impact of thevertical residual motion on the actual ver-tical motion of chemical species. Thisdepends on the degree of isolation. Forexample, if a model has spurious mixingacross the vortex edge, then the descentof chemical species will reflect the dia-batic descent in a broad region includingthe surf zone, rather than within the vor-tex. Assuming that the degree of isola-tion is correct, then it is possible to makea direct comparison between models andmeasurements by examining the ascentor descent rate of tracer isopleths. A wellknown example is the ascent rates oftropical H2O mixing ratios, which createthe ‘tape recorder’ phenomenon in mix-ing ratio time series plots.

Meridional circulation. The combinedeffect of the above processes determinesthe Brewer-Dobson circulation. Bothhorizontal mixing and the residual circu-lation are driven in large measure by themomentum deposition (wave drag) fromplanetary waves propagating from thetroposphere into the stratosphere, withmore wave drag leading to a strongerBrewer-Dobson circulation in bothrespects. Because planetary waves canonly propagate into the stratospherewhen the winds are westerly, the Brewer-Dobson circulation is restricted to thewinter hemisphere. The wave drag iseasily quantified from the net planetarywave flux into the stratosphere, nomi-nally taken to be v’T’ (vertical EP flux) at100 hPa. The relationship between thiswave flux and the residual circulation is

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Figure 2. Vortex isolation inferred from tracerprobability distribution functions (PDFs). Timeevolution of PDFs of CH4 distributions on the450K isentropic surface in the SH extratropicsfrom September through November in bothHALOE data (from 1992-1999) and from threeconsecutive years of simulation from theGoddard 3D CTM using winds from theGoddard Finite-Volume GCM (FVGCM). Thelatitude range of the “vortex” PDFs is 60-80Swhile the latitude range of the “surf zone”PDFs is 40-60S. Dashed lines represent thepeak mixing ratio of the September PDFs inorder to help judge which way the PDF is shif-ting as the vortex erodes. Courtesy of SusanStrahan, NASA Goddard Space Flight Center.

theoretical understanding of transport inthe UTLS is relatively poor. This pre-sents a challenge to determine appropri-ate diagnostics for model-measurementcomparison.

Subtropical and polar mixing barriers.With respect to the degree of isolation,useful information can be obtained frominstantaneous snapshots of tracer fields,which makes the model-measurementcomparison straightforward. For thispurpose there is a wealth of high-qualityobservational data available. A simplecheck on the degree of isolation is pro-vided by the sharpness of latitudinal gra-dients of long-lived species (CH4, N2O,CFC11). However, since these gradientscan be smeared out in zonal means, it isimportant to look at slices perpendicularto the mixing barrier (approximately, butnot necessarily, at a single longitude).Equivalent latitude is an effective tool to

create composites in the polar regions,but it is probably not viable in the tro-pics. A way to avoid latitudinal smearingwithout relying on equivalent latitude isto look at tracer Probability DistributionFunctions (PDFs) (see Figure 2), whichallow a direct model-measurement com-parison. The degree of isolation can bediagnosed in more detail from the struc-ture of chemical correlations, thoughtheir interpretation is not always straight-forward. Within the very lowest part ofthe overworld in the tropics, just abovethe tropopause, where the tropical mixingbarrier appears to be fairly leaky, hori-zontal transport into midlatitudes canalso be quantified by the propagation ofthe annual cycle in CO2 and H2O, whichhas been well observed in aircraft mea-surements. Finally, transport out of thetropics can also be quantified in terms ofstreamers, but the quantification dependson how the streamers are defined.

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quantified, through temperature, in thedynamics diagnostics (Table 1). Withregard to chemical transport, the seasonalcycle of O3 in the extratropics exhibits amarked build-up during the winter-spring period due to the Brewer-Dobsoncirculation. Years with greater planetarywave flux also have a greater ozonebuild-up, a relationship that is well esta-blished from observations and provides agood diagnostic for CCM validation.

The Brewer-Dobson circulation alsodetermines the mean age of air.Unfortunately, the possibilities for directcomparison with data are more limitedthan for the processes described above,because the measurement precisionrequirements are so stringent that, at pre-sent, only in situ data can be used. Thisparticularly limits comparisons in theupper stratosphere. Nevertheless, inNASA’s Models and MeasurementsIntercomparison II, mean age of air wasfound to be a very powerful diagnosticfor identifying model deficiencies. Meanage can be validated from measurementsof long-lived species that have linearlyincreasing concentrations (e.g., SF6, CO2).Propagation of the annual cycle of meanage can be validated from CO2 measure-ments in the overworld (and H2O in thetropics). However, other components ofthe age spectrum (e.g., semi-annual, bien-nial) are very difficult to validate.

UTLS transport. In contrast to thestratospheric “overworld” discussedabove, transport in the UTLS region isfar more complex. Yet many of the sameconcepts appear to be useful for valida-tion. The extratropical tropopause is abarrier to quasi-horizontal mixing, caus-ing a significant contrast in many chemi-cal species between the lowermoststratosphere and the troposphere. Thedegree of isolation can be assessed bythe sharpness of vertical gradients at thetropopause (vertical gradients becausetropopause height changes with lati-tude), and with chemical correlations(e.g., O3 vs. CO). For the former there isplentiful ozone sonde data, and for thelatter there is a wealth of aircraft data.These data are not sufficient to establishclimatologies, but are nevertheless use-ful for process-based validation.However, it is important to comparemodels and measurements at similarlongitudes, because there is significantlongitudinal variation of the dynamicalfeatures in the UTLS (especially thetropopause). Unlike in the stratosphericoverworld, UTLS transport is not quasi-zonal, and many chemical species arenot sufficiently long-lived to be well-mixed longitudinally. There is a well-established relationship between varia-

tions in total O3 and in various tropo-spheric meteorological indicators, mostnotably tropopause height. While theprecise mechanism for this relationshipis not well understood - most likely, thevarious meteorological indicators are alljust proxies for the same process - therelationship is robust and, therefore, alsoprovides a potentially important diag-nostic for CCM validation. Ozonesondeobservations show that tropopauseheight variations affect O3 profilesthrough the depth of the lowermoststratosphere, up to about 20 km. TheTropical Tropopause Layer (TTL) is acritical part of the atmosphere in theUTLS to resolve properly in CCMs.Processes in this layer are important forsetting chemical boundary conditionsfor the stratosphere and for understand-ing upper tropospheric chemistry andclimate. The TTL region features largehorizontal inhomogeneities, localisedrapid vertical transport by convection,and many scales of dynamic variationdue to waves. Many of these processescannot be explicitly resolved by CCMs,but their effects must be treated reason-ably to appropriately simulate the UTLSand to simulate climatic changes in themiddle atmosphere. Validation can beaccomplished by comparing the hori-zontal and vertical structure of the TTLto observations (e.g. the SHADOZ net-work of ozonesondes, GPS observationsof temperatures and wave induced vari-ability in the TTL or satellite observa-tions from instruments, such as AIRSand MODIS).

Radiation

The representation of the radiation fieldis a crucial aspect in CCMs if ozoneabundances and temperature changesare to be accurately calculated in thepresent and future atmosphere.Radiation affects CCMs through photo-lysis rate and heating rate calculations.Chemically active constituents, such asozone, are strongly affected by photoly-sis rates, which are derived from theradiation field. At the same time thesetrace gases feed back on temperatureand, thus, circulation through the radia-tive heating rates. At present, mostmodels calculate radiative heating ratesand photolysis rates in an inconsistentmanner. For example, the sphericalgeometry of the Earth might be includedin the photolysis rate calculation, butnot in the heating rate calculation. Alsodifferent radiation schemes are usuallyemployed for the two calculations.Ideally, such inconsistencies would beavoided. However, here we evaluatethese two calculations separately.

Solar UV-visible photolysis in thestratosphere. Photolysis rates in thestratosphere control the abundance ofmany chemical constituents that in turncontrol the production and loss of ozone.A photolysis rate generally requiresknowledge of the actinic fluxes at solarand UV-visible wavelengths (190-800 nm) as a function of altitude andsolar zenith angle. Accurate calculationsof these fluxes require accurate represen-tation of scattering, albedo and refrac-tion. Particular concerns in photolysisrate calculations for the lower strato-sphere are the effect of troposphericcloudiness, which can significantlyincrease the rates for certain gases andphotolysis at solar zenith angles greaterthan 90°. Diagnostic parameters for pho-tolysis rates in CCM model comparisonsinclude the radiative transfer of UV-visi-ble wavelengths and calculated rates forindividual gases. Key variables in suchmodel comparisons are the distributionsof pressure, ozone, stratospheric aerosolsand tropospheric clouds. As a minimumtest, the photolysis rates of O3 and NO2should be stored as three-dimensionalfields at local noon and compared toobservations. In addition, actinic fluxesat the ground in different wavelengthintervals should be compared.

Radiative heating rates. The radiativeheating rate calculation is the fundamen-tal link between ozone and climate. Asthis calculation plays the central part inCCM feedbacks, it is extremely difficultto separate cause and effect in a fullycoupled model. Radiative heating ratecalculations can only be truly evaluatedin an offline comparison of radiationschemes. Currently, the lack of this com-parison is one of the most important limitations in understanding CCM diffe-rences and we strongly advocate such acomparison be initiated. A set of stan-dardised background atmospheres andradiation scheme inputs should be com-piled, along with a reference set of calcu-lations from several state of the art line-by-line and scattering (e.g., Discrete-Ordinate) models. These should then bemade available to the community to eva-luate their own CCM radiation scheme.Differences in radiative heating rates andtrace gas fields can then be used to eva-luate differences between the globallyaveraged climatological temperature ofCCMs and their temperature response tochanges in greenhouse gases loadingsand other perturbations.

Radiative heating within an onlineframework. To evaluate radiative heat-ing within an online framework the long-term global-mean temperature climato-logy of CCMs can be compared to

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observations (see Figure 3 p. I). Anonline framework allows a combined testof the model’s background atmosphereand radiative heating profile. Also, theglobally averaged transient temperaturechanges over both a single year and thepast ~25 years can be compared toStratospheric Sounding Unit andMicrowave Sounding Unit satelliteobservations. This tests both the evolu-tion of forcing agents, as well as theradiative heating and the radiative rela-xation time in the model.

Stratospheric Chemistry and Microphysics

Chemistry is clearly a natural processcontrolling the distribution of ozone inthe atmosphere. Virtually all reactionrates are to a varying extent temperaturedependent, providing one of the ways inwhich chemistry and dynamics are cou-pled. The importance of chemistry rela-tive to other processes, such as transport,varies substantially depending on thelocal solar conditions, as well as altitude.In the upper stratosphere transport playsa role by controlling the concentrationsof the long-lived tracers, such as activechlorine, but photochemical timescalesare so short that transport has a minimaldirect impact on ozone. However, in thelower stratosphere, the photochemicaltimescales are rather longer (typically ofthe order of months) and interactionswith dynamics are complex and difficultto model accurately. Aerosols also mayhave an important role to play in thelower stratosphere since, in addition totheir radiative impact, chemical reac-tions can take place within or on the par-ticles and these reactions may lead toadditional ozone depletion. Solar condi-tions are also important: for example, inpolar night the distribution of chemicalspecies is quite different to that in mid-latitudes where a clear diurnal variationin solar insolation occurs. Also, photo-chemical conditions are different inpolar summer when the impact of thecontinuous daylight may be to photolysethe reservoir species entirely, dependingon altitude. The different timescale of theprocesses in different parts of the atmo-sphere implies that a variety of model-ling techniques can be effective.

Photochemical mechanisms and shorttimescale chemical processes. In thelist of processes for stratospheric che-mistry and microphysics, one of the mostimportant tasks is to verify the perfor-mance of the underlying photochemicalmechanisms, including the computationof photolysis rates. Model comparisons

of this sort need to be completed usingbox model versions of the code used inthe CCM, looking at timescales up to oneweek or so. Future studies can followthe example of the ‘model and measure-ment tests’ of Park et al. (1999). Very fewmeasurements exist for direct compari-son of photolysis rates (e.g., Gao et al.,2001), but there have been some attemptsat inferring photolysis rates from chemi-cal measurements. The comparisonscould be made using the different modelcalculations for ozone loss and produc-tion in each of the catalytic cycles sup-ported by Lagrangian studies usingobservations from a wide range ofsources, both in situ and remote. Modeldiurnal variations could also be com-pared and verified with a limited rangeof observations.

Long timescale chemical processes.The investigation of long timescale pho-tochemical processes needs to be com-pleted within the CCM itself as tracertransport has a significant impact. Allthe model chemical constituents need tobe output three-dimensionally, as well asthe appropriate dynamical variables,such as temperatures. One instanta-neous “snapshot” per month should besufficient for the purpose of comparingthe abundances of model reservoirs andprecursors to the radicals, which directlyaffect ozone. The inter-relations betweenlong-lived tracers also need to be compared in detail with similar resultsdetermined from space-based or in situobservations.

Summer processes and polar processesin winter/spring. In the summer, thepolar regions are a special case of atmo-spheric chemistry because of the continu-ous or near continuous daylight. Theseconditions have revealed some possiblediscrepancies in NOx chemistry. Thishas an impact on ozone amounts directlyin the polar regions and also in mid-latitudes via transport from the polarregions. In the winter/spring period, lowtemperatures lead to the formation ofcondensed matter and heterogeneouschemistry becomes important. Someaspects of heterogeneous chemistry canbe investigated in box model simulations,but because of the possible importance ofdenitrification and dehydration, as wellas transport, a full three-dimensionalmodel is required for a complete analy-sis. Polar processes require an extensiveset of chemical and particle concentra-tion values within the polar regions withdaily frequency. One particular diagnos-tic, designed to address overall modelozone depletion in polar regions, requiresthe addition of a passive tracer to theCCM. The tracer should be initialised on

a specific date in the beginning of thewinter identically to the ozone on thatday. Thereafter, assuming that modeltransport errors are negligible, the diffe-rence between the photochemically com-puted ozone and the passive tracer provides an indication of the chemicalozone loss. Observations (Rex et al., 2003)indicate that chemical ozone loss andPolar Stratospheric Cloud (PSC) volumeare linearly correlated (see Figure 4 p. I).Comparisons with this correlation wouldbe a useful test of the ability of a model tosimulate accurately the polar chemicalozone loss in the presence of PSCs.

Denitrification & Dehydration. Largepolar ozone losses in both hemispheresoccur in winters that are sufficiently coldfor denitrification and dehydration.However, the current representations ofthese processes in CCMs are simplistic,leading to large uncertainties in polarozone loss and in the impact on mid-latitudes. This is further complicated by(a) the poor understanding of the mecha-nism by which denitrification occurs and(b) CCM temperature biases in the polarvortex. The CCM representation of deni-trification can be investigated byanalysing the key nitrogen containingspecies, NOy and HNO3, as a function ofthe well-conserved tracers N2O and CH4.Remote and in situ data can be used toclarify these relationships and indicateany local loss in NOy or HNO3.Similarly, the sum H2O + 2CH4 isapproximately conserved in the strato-sphere, so significant departures wouldindicate dehydration or possibly settlingfrom above.

Aerosol processes. Reactions involvingsulphate aerosol are known to affect theproduction and loss balance of strato-spheric ozone. Not all CCMs are in aposition to investigate these processes indetail, as in some instances a completesulphur reaction set is needed.Nonetheless, even for those models witha passive sulphate amount, it would beof interest to complete simulationsdescribing the impact of a major volcaniceruption, such as that of Mt. Pinatubo.

Aerosols & Cloud Microphysics. Aerosoland cloud related processes affect thewhole UTLS region. There is a need toinvestigate these processes in CCMs andvalidate them using the available satelliteand aircraft data. The required modelvariables are liquid water and ice, tem-perature and aerosols, and they will berequired at a relatively high spatial andtemporal frequency, i.e., at least everythree days and for every model grid pointin the UTLS region. Further output ofchemical constituents and potential

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vorticity would be useful to examine heterogeneous chemistry and the dyna-mical structure of the tropopause.

The Way Ahead

Of the comprehensive suite of diagnos-tics for stratospheric CCMs listed inTable 1, several have been applied beforeto a range of models (Austin et al., 2003;Pawson et al., 2000; Park et al., 1999),but many have not. Some models needfurther development before the diagnos-tics can be applied. Thus, while clearlydesirable, it is a major task to perform allthese diagnoses given the complexity ofthe CCMs and the often subtle changesunder consideration. A step-wiseapproach is required for the use of theTable. In practice, modelling groupsneed to develop their own prioritiesamong these diagnostics. The choiceswill depend on the known strengths andweaknesses of each model, the processesand constituents already included, andthe existing output from runs alreadyperformed. It will also depend on thescientific focus of each modelling groupand the issue being addressed. Forexample, predictions of polar ozone losswill have more credibility if a model hasbeen shown to compare well with diag-nostics, such as ozone loss versus PSCvolume, v’T’, and ClOx, NOy, etc. In thiscase, good performance against TTLdiagnostics is less relevant. Over timeeach model will gradually increase thenumber of tests applied and overall con-fidence will increase.

The lasting impact and the full benefitfrom the workshop will come from con-certed validation activities based on theTable of Processes. In order for theseactivities to succeed over the next severalyears, broad support is needed from theatmospheric sciences community and itsmanagers. It is important that the valida-tion procedures and goals defined forthese activities are accepted at the startand valued by all participants in thisjoint exercise.

SPARC working groups are being setup so that real progress can be made inthe next couple of years in time for thenext WMO/UNEP and IPCC assess-ments. The SPARC GRIPS group iscontinuing the work on the compa-risons for the dynamics issues. SPARCgroups have been formed on CCMchemistry and radiation comparisonsand they are defining plans for theirissues. Up-dated information is avail-able at http://www.pa.op.dlr.de/ work-shops/ccm2003/ together with thenames of people coordinating the vari-

ous activities. All scientists interestedin participating should contact theappropriate coordinating scientist.

To facilitate this process-oriented valida-tion of CCMs, we intend to provide par-ticipants with access to diagnostic soft-ware packages. These routines will bearchived in a central location. The goalin supplying such software is to simplifysuch activities as quality control ofmodel output, calculation of more com-plex model diagnostics, statistical evalu-ation of model/data differences andgraphical display of results. Use of thissoftware is not mandatory. Rather, theintent is to make it easier for groups tocompute a broad range of calculations in a reasonably consistent way.Centralised software repositories havebeen of great benefit in other ModelIntercomparison Programs (“MIPs”),such as the Atmospheric ModelIntercomparison Project (AMIP) and theCoupled Model Intercomparison Project(CMIP). These have freely supplied soft-ware for quality control of model output,data visualisation and interpolation ofboundary condition datasets to a specificmodel grid. The CCM community canbenefit from the experiences gained du-ring previous model intercomparisonexercises, particularly in terms of experi-mental design, definition of standardmodel output and statistical aspects ofmodel-data comparisons. Softwaredeveloped in the course of previousMIPs, such as “performance portraits”and Taylor diagrams, provide usefulmeans of summarising many differentaspects of climate model performance.In collaboration with groups, such as theProgram for Climate Model Diagnosisand Intercomparison (PCMDI), weintend to modify these diagnostic toolsin order to suit the specific needs of theCCM community.

This suite of processes and diagnosticsshould become a benchmark for valida-tion. Confidence in the performance ofCCMs will increase as more modelattributes become validated against thewhole suite of diagnostics. Further,new models can be evaluated against anacknowledged, benchmark set of diag-nostics as the models are developed. Atthe same time, the diagnostics them-selves should develop as experience isgained and as new measurementsbecome available allowing moreprocesses to be diagnosed. It is hopedthat this workshop has laid thegroundwork to a more comprehensiveapproach to CCM validation, which willbe developed by all scientists whobecome involved, irrespective of whetherthey attended the workshop or not.

Acknowledgements

We wish to thank all the agencies thatsupported this workshop. The workshopwas held under the auspices of theInstitute for Atmospheric Physics of theGerman Aerospace Center (DLR), the EUresearch cluster OCLI (Ozone CLimateInteractions), and SPARC.

References

Austin, J., et al. Uncertainties and assessmentsof chemistry-climate models of the strato-sphere, Atmos. Chem. Phys., 3, 1-27, 2003.

Eyring V., et al. Brief report on theWorkshop on Process-Oriented Validation ofCoupled Chemistry-Climate Models, SPARCNewsletter N° 22, 2004.

Gao, R.S., et al. Observational evidence forthe role of denitrification in Arctic strato-spheric ozone loss, Geophys. Res. Let., 28,15, 2879-2882, 2001

Gibson, J.K., et al. ERA description, ECMWFRe-Analysis Project Report Series, 1, 1-72,1997.

Hayashi, Y., Space-time spectral analysisand its applications to atmospheric waves, J. Meteor. Soc. Japan, 60, 156-171, 1982.

Hein, R., et al. Results of an interactively cou-pled atmospheric chemistry-general circula-tion model: Comparison with observations,Ann. Geophysicae, 19, 435-457, 2001.

Newman, P.A., et al. What controls the tem-perature of the Arctic stratosphere duringspring?, J. Geophys. Res., 106, 19999-20010,2001.

Park, J.H., et al. Models and MeasurementsIntercomparison II, NASA/TM-1999-209554,1999.

Pawson, S., et al. The GCM-RealityIntercomparison Project for SPARC:Scientific Issues and Initial Results, Bull.Am. Meteorol. Soc., 81, 781-796, 2000.

Rex, M., et al. Arctic ozone loss and climatechange, Geophys. Res. Let., 31, doi:10.1029/2003GL018844, 2004.

WMO, Scientific Assessment of OzoneDepletion: 2002, Global Ozone Research andMonitoring Project - Report No. 47, 498 pp,Geneva, 2003.

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Report on the Assessment of Stratospheric AerosolProperties: New Data Record, but no Trend

Larry W. Thomason, NASA Langley Research Center, USA (l.w.Thomason@larc.nasa.gov)Thomas Peter, Swiss Federal Institute of Technology, Switzerland (Thomas.Peter@ethz.ch)Contributors to this work have been the Chapter Leads: S. Bekki (France), H. Bingemer (Germany),C. Brogniez (France), K. Carslaw (UK), T. Deshler (USA), P. Hamill (USA), B. Kärcher (Germany),J. Notholt (Germany), E. Weatherhead (USA), D. Weisenstein (USA), plus many others colleagues

Introduction

Assessments of stratospheric ozone havebeen conducted for nearly two decadesand have evolved from describing ozonemorphology to estimating ozone trends,and then to attribution of those trends.The stratospheric aerosol has only beenintegrated in assessments in the contextof their effects on ozone chemistry andhas not been critically evaluated itself.As a result, SPARC has sponsored theAssessment of Stratospheric AerosolProperties (ASAP). Initially, weexpected the assessment to consist pri-marily of an evaluation of availablestratospheric aerosol measurements,however, it rapidly became apparent thatthe lack of previous groundwork made amore expansive effort worthwhile. As aresult, the scope of ASAP expanded toinclude 5 primary components referringto stratospheric aerosols: (1) Processes,(2) Precursors, (3) Measurements, (4) Trends, and (5) Modelling. Herein,we will describe the contents of thesesections beginning with some of ASAP’skey findings.

Key Findings

• Unlike gas species, aerosol cannot becharacterised by a single quantity but hasa size distribution and composition. Thevast bulk of existing data does not com-prise a complete measurement set and asa result many parameters required forscientific or intercomparison purposesare derived indirectly from the base mea-surement. This is true for space-basedmeasurements where only bulk extinc-tion is measured, but also true in degreefor most ground-based and in situ sys-tems. The fact that each system mea-sures a different set of parameters greatlycomplicates almost every stage of mea-surement comparisons.• Space-based and in situ measurementsof aerosol parameters tend to be consis-tent following significant volcanic eventslike El Chichon and Mt. Pinatubo.However, during periods of very lowaerosol loading, this consistency breaksdown and significant differences existbetween systems for key parameters,including aerosol surface area densityand extinction.

• Since the beginning of systematicstratospheric aerosol measurementsthere have been three periods with littleor no volcanic perturbation, thoughonly the period from 1999 onwards canbe confidently identified as free of vol-canic aerosols. The other periods (late1970’s and late 1980’s) are too short induration to evaluate, given the complexvariability observed. The period in the1980’s seems likely to have not reacheda stable non-volcanic level. Trendsderived from the late 1970’s to the cur-rent period are likely to completelyencompass a value of zero.• There is general agreement betweenmeasured OCS (carbonyl sulfide) andmodelling of its transformation to sul-fate aerosol, and observed aerosols.However, there is a significant dearth ofSO2 measurements, and the role of tro-pospheric SO2 in the stratosphericaerosol budget - while significant -remains a matter of some guesswork.In addition, it is not well understoodwhether decreasing global human-derived SO2 emissions or increasingemissions in low latitude developingcountries, such as China, dominate thehuman component of SO2 transportacross the tropical tropopause.• While the actual removal of aerosolfrom the stratosphere to the tropo-sphere is predominantly associatedwith tropopause folds, sedimentationplays an important role in the verticalredistribution of aerosol throughout thestratosphere.

Chapter 1: Processes

The aerosol processes section high-lights the lifecycle of stratosphericaerosol (Figure 1 p. II) that involvesprocesses of precursor gas and aerosolinput to the stratosphere through thetropical tropopause, the transport andtransformation of the aerosol within theBrewer-Dobson circulation, and theremoval of aerosol in air traversing theextra-tropical tropopause and throughgravitational settling. The non-volcanicstratospheric aerosol is formed prima-rily through binary homogeneousnucleation of sulfuric acid and water in rising air masses close to the tropicaltropopause (e.g., Brock et al., 1995).

The aerosol in the tropical regions israpidly transported zonally with themean stratospheric winds, while thetransport is restricted meridionally bythe transport barrier of the tropical pipein the 15°-30° latitude range. Thisreduced transport is most effective ataltitudes between about 21 and 30 kmand poleward transport at lower alti-tudes is more rapid. After a volcaniceruption the transport barrier of the“leaky tropical pipe” leads to the build-up of a tropical reservoir of aerosolmass, first described by Trepte andHitchman (1992). This is also reflectedin Figure 2 (p. II), where 1992 is theyear after the eruption of Mt. Pinatubo.

The aerosol in the air masses transportedinto the mid and high latitudes continuesto evolve through microphysicalprocesses, such as evaporation at theupper edge of the aerosol layer andnucleation/re-condensation duringdescent. The air descends diabatically tothe lowermost stratosphere where it caneventually be removed in the tropo-sphere through quasi-isentropic transportof the air in tropopause folds that is thedominant removal mechanisms forstratospheric aerosol. Furthermore,throughout the lifetime of the aerosol,gravitational settling adds to the removalof these particles. Due to the long life-time of the particles, their sedimentationvelocities (~100 m/month for particleswith 0.1�m radius and strongly growingfor larger ones) cannot be neglected.Additional removal occurs over the poleswhen the sulfuric acid particles serve assites for polar stratospheric cloud (PSC)particle formation. Some PSC particlescomposed of nitric acid hydrate or icecan grow to several microns in diameterand sediment rapidly to the tropopause,taking included sulfuric acid particleswith them. Observations clearly showthe seasonal reduction in polar aerosolmass following periods of PSCs.

Chapter 2: StratosphericAerosol Precursors

The direct gaseous precursor for thestratospheric aerosol sulfate is sulfuricacid (H2SO4). With the exception of

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sporadic direct injections from vol-canic eruptions, stratospheric H2SO4originates primarily from OCS photo-lysis and in situ oxidation of SO2, OCSand other reduced sulfur gases reach-ing the stratosphere including DMS(CH3SCH3), H2S, CH3SH, and CS2.Since these species originate at theEarth’s surface, they are reliant ondeep convection events above the con-tinents (particularly in the tropics) toreach the lower part of the TropicalTransition Layer (TTL). In the TTL,air carrying the sulfur compounds isquasi-horizontally transported overwide distances and eventually ascendsinto the stratosphere. The largestemissions of sulfur-containing com-pounds at the surface are SO2 followedby DMS, H2S, CH3SH and OCS andCS2. It is now believed that OCS andSO2 are the main precursor gases forthe formation of the stratosphericaerosol layer. Although the emissionsof OCS are much smaller than those ofSO2 and DMS, its long lifetime allowsit to reach the stratosphere.Conversely, SO2 can reach the TTLdespite having a short lifetime in thetroposphere due to rapid transport ofair masses by deep convection to thebottom of the TTL. The compositionof the TTL is presently not fully char-acterised with respect to the sulfurcontaining gases and radicals. On thewhole, the knowledge of the sea-sonal and longitudinal variability of SO2 and HOx in the TTL is very limited.

The long-term sulfur flux into thestratosphere is expected to show somevariability. First, the long-term trendof OCS, as measured by remote sens-ing techniques, is found to be about - 0.25%/y throughout the last 20 years.Second, the emission patterns of SO2have changed throughout the lastdecades. Long-term observations ofSO2 have been performed in situ atnumerous locations. While theanthropogenic emissions in theNorthern Hemisphere have decreased,emissions in Asia, China and the tropi-cal biomass burning have increased. Itis not clear to what extent theseprocesses might compensate eachother. In addition, the oxidationcapacity (OH and HOx concentrations)in the upper tropical troposphere haschanged within the last decades.Since the main sink of SO2 is its reac-tion with OH, changes in the OH con-centration have a strong impact on theSO2 burden. Furthermore, recentstudies indicate that the OH concen-tration within the TTL is by a factor 2-4 higher than previously assumed.

Chapter 3: AerosolMeasurement Systems

Stratospheric aerosol measurements sys-tems were broadly divided into twogroups. One group consists of systemswith long continuous records, such asthe Stratospheric Aerosol and GasExperiment (SAGE) series and theHalogen Occultation Experiment(HALOE) space-based systems, the bal-loon-borne University of WyomingOptical Particle Counter (OPC), and lidarsystems like that at Garmisch-Partenkirchen, Germany. The other setconsists of either episodic measurementslike FCAS (Focus Cavity AerosolSpectrometer) and FSSP-300 (ForwardScattering Spectrometer Probe), whichare deployed primarily as a part of fieldcampaigns like the SAGE III Ozone LossValidation Experiment (SOLVE), or ofshorter term space-based measurementslike the Cryogenic Limb Array EtalonSpectrometer (CLAES). For ASAP, wefocused on the former group.

HALOE and SAGE, and also the PolarOzone and Aerosol Measurement(POAM III), make use of the solar occul-tation technique to measure atmospherictransmission along the line of sightbetween the spacecraft and the Sunalong paths that pass through the atmo-sphere (hence the Sun, relative to theinstrument, is being occulted orobscured). This technique is well suitedfor situations in which horizontal inho-mogeneity is not a significant concernand where the optical depth is relativelylow, features which are generally charac-teristic of the stratosphere. Using thisstrategy, HALOE (1991-present) makesaerosol extinction measurements in theinfrared at 2.45, 3.40, 3.46 and 5.26 �m.The SAGE series of instruments consistsof three instruments: the StratosphericAerosol Measurement (SAM II; 1978-1993), SAGE (1979-1981), and SAGE II(1984-present). All SAGE series instru-ments operate in the visible/nearinfrared and measure aerosol extinctionat one or more wavelengths includingone close to 1000 nm for all instruments.

The OPC, a balloon-borne system, wasoriginally designed in the 1960s [Rosen,1964] and has been routinely launchedfrom Laramie, Wyoming (USA) since1971. Given its portability it has alsobeen extensively launched fromAntarctica and was also launched fromLauder, New Zealand for several yearsduring the 1990s and is frequentlydeployed during field campaigns, suchas SOLVE (2000) and SOLVE II (2003).The instrument, a white light counter

measuring aerosol scattering at 25°(prior to 1989) or 40° (1989 onwards) inthe forward direction, measures parti-cles one at a time and uses Mie scatter-ing theory to convert from brightness toparticle size in 2 to 12 size bins andfrom 0.15 to either 2.0 or 10 �m[Hofmann and Deshler, 1991; Deshler etal., 2003]. A particle size distributionis derived by fitting either a single orbi-modal log-normal to the binned data.

Chapter 4: AerosolMeasurement Record

Derived quantities like Surface AreaDensity (SAD) and effective radius arederived from SAGE data using a tech-nique similar to that in Thomason et al.[1997]. The primary change from theprevious version was the use of errorbars to weight the measurements. ForHALOE data, derived quantities likeSAD are determined using the methoddescribed in Hervig et al. [1998].Relative to versions prior to 2002, thesulfate refractive index data has beenupdated to that of Tisdale et al. [1998]from that of Palmer and Williams [1975].The change resulted in an reduction of~ 25 % in SAD from the previouslyarchived data set. Both SAGE andHALOE data sets have identified andeliminated obvious occurrences ofclouds.

An endemic problem with these data setsbecomes obvious when we attempt to doa critical comparison. Since none ofthese systems measure the same aerosolattributes and, thus, the comparisons aredependent on the robustness of the con-versions as the quality of the basic mea-sured quantities themselves. This is wellillustrated by measurements of SAD inFigure 3 (p. II). Here we see that compa-risons of SAD between SAGE II and theOPC are typically in reasonable agree-ment during high aerosol loading, suchas that following the Mt. Pinatubo erup-tion of 1991. On the other hand, whenaerosol loading is low (either at high alti-tudes or at lower altitudes in the later1990’s or 2000’s), SAGE II SAD is biasedlow by as much as a factor of 2 relativeto the OPC values. This is not unex-pected since low aerosol loading is alsoassociated with generally smaller aerosolsizes. Measurements made at visible/near infrared wavelengths are primarilydriven by scattering and increasinglyinsensitive to particles smaller than 0.1 �m. At that point, even if the extinc-tion measurements themselves remainrobust, the derived SAD becomes highlydependent on how the derived algorithm‘chooses’ to fill the part of the size

14

distribution that is effectively invisible.Since the SAGE II algorithm tends to putrelatively little SAD in the smaller parti-cle sizes, the bias and its sign is notunexpected.

Comparisons of HALOE and OPC extinc-tion derived for SAGE measurements at1020 nm are shown in Figure 4. As inthe case for SAD, the agreement is quitereasonable for elevated extinction.However, in this case, when extinctiondrops toward non-volcanic levels a sys-tematic bias particularly between SAGEII and the OPC values (that approaches afactor of five by the end of the period) isevident, even though the aerosol levelsthemselves are thought to be well withinthe dynamic range of both instruments.HALOE generally agrees better withSAGE II during this period but occasio-nally agrees better with the OPC values.The bias is in the opposite sense of theSAD bias (SAGE II greater than the OPCfor extinction). Interestingly, compa-risons at the shorter wavelengths are con-siderably better than those at 1020 nmand would imply a difference in thelarger end of the aerosol size distributionbetween the OPC and that implied by theSAGE II measurements. Generally,SAGE II 1020 nm extinction measure-ments are consistent with those ofPOAM III and other members of theSAGE series [Thomason and Taha, 2003]and, thus, not an outlier. Such large dif-ferences in extinction values also reduceour confidence in our conclusionsregarding the differences between sys-tems in other quantities like SAD andadditional work in this area is required.

Chapter 5: Trends

For trend analysis, we decided to focuson the primary measured quantities of themeasurement systems: extinction at 1000 nm for the SAGE series, the 0.15 and0.25 �m bins for the OPC, and integratedstratospheric backscatter for long recordlidar systems at Garmisch-Partenkirchen(Germany), Mauna Loa (USA) andHampton (USA). It is not possible toevaluate trends in the stratosphericaerosol in the same way that trends arecomputed for species like ozone or watervapour due to volcanic impacts that havecaused perturbations as large as a factor of1000 at some altitudes and locations. Asof this writing, this analysis has not beencompleted and the following discussionis still preliminary.

With the long recovery time from majorevents and the observed complex sea-sonal and quasi-biennial components toaerosol variability, stable, multi-yearperiods are necessary to confidentlyidentify volcanically perturbed periods.Three time periods have been consideredas candidates for non-volcanic periods.Two of these, the late 1970’s and late1980’s/early 1990’s are of short durationand are difficult to use. The third periodstarts no later than 1999 and continuesuntil late 2002, when eruptions by Ruang(Indonesia) and Reventador (Ecuador) atleast temporarily ended the latest quies-cent period. The late 1980’s period alsoappears unlikely to qualify as back-ground since, particularly the tropics,exhibit an uninterrupted decrease fromthe El Chichon/Nevado del Ruiz erup-tions of 1982 and 1985 [Thomason et al.,

1997]. Finally, differences between the1970’s (despite concerns regarding itsuse) and the 2000’s are small and itseems likely that the uncertainties in anyderived trend will easily include zero.

Chapter 6: Modelling

The overall object of the ASAP model-ling investigation was to determinewhether transport of sulfur compounds(primarily SO2 and OCS) from the tro-posphere and known physical processescan explain the distribution and vari-ability of the stratospheric aerosol layer.Models, since they encompass theknowledge of coupled aerosol processes,are the primary tools to test our quantita-tive understanding of processes control-ling the formation and evolution of theaerosol layer. As a result, comparisonsbetween models and observations formthe core of this study. The models par-ticipating in this effort were developedfor modelling stratospheric aerosol andinclude AER (D. Weisenstein), CNRS (S. Bekki), LASP (M. Mills), MPI (C. Timmreck), and ULAQ (G. Pitari).These models are well-established 2-Dand 3-D aerosol-chemistry-transportmodels that contain standard chemistryincluding that for sulfur, but they differin their implementation for aerosol for-mation and evolution, as well as in othercomponents, such as in their handling ofthe tropopause boundary conditions.

Comparisons of the models to precursorgas measurements are generally promis-ing. In particular, agreement among themodels and measurements of OCS in thetropics are within the error bars. This isreassuring since this region is where tropospheric sources gases enter thestratosphere and where the major chemi-cal loss of OCS occurs. The agreementbetween models and observationsremains fairly good at other latitudes,though the models show more variabilityamong themselves. For SO2 in the non-volcanic stratosphere, the models aremainly compared against one another,since the only observation of SO2 undernon-volcanic conditions comes from a

Figure 4. Time series at three altitudes overLaramie of aerosol extinction at 1020 nm.SAGE II (◊) measurements are compared toextinctions calculated from OPC (—) andHALOE (□ ) size distributions. HALOE andSAGE II measurements between 41°N and42°N latitude and 245°E and 265°E longitudewere used. Vertical bars on the occasionalSAGE II measurement indicate ± 50 %. TheSAGE II uncertainties are less than this, andthese bars serve only to add perspective.This time series is comprised of 68 SAGE II,178 OPC and 31 HALOE measurements.

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Report on Chapman Conference on Gravity WaveProcesses and Parameterisation

Waikoloa, Hawaii, USA, 9-14 January 2004Kevin Hamilton, University of Hawaii, USA (kph@hawaii.edu)

single ATMOS profile from 1985[Rinsland, 1995] and, therefore, its distri-bution is not well known. For this pro-file, the models do not agree well exceptLASP above 33 km. The models tend toagree among themselves between 20 and30 km in the tropics, however, model dif-ferences in SO2 much like those for OCSare much larger at higher latitudes mostlikely due to differences in transport.Model-computed aerosol extinctionsgenerally agree with SAGE II andHALOE observations in magnitude andin latitudinal gradients during lowaerosol loading periods. This is trueabove 20 km where the models them-selves also tend to agree, but to a lesserdegree below 20 km where some sub-stantial divergence between the modelsthemselves can be observed. Comparedto SAGE II measurements below 20 km,the model 525 nm extinctions tend tostraddle the observations, while themodel extinctions at 1020 nm tend tounderestimate the observed extinction.This suggests that the models have redis-tributed some of the aerosol from largerto smaller sizes relate to that suggestedby the observations. Above 20 km, theagreement between the models andSAGE II-derived SAD is comparable tothe agreement found for extinction.Below 20 km, the SAGE II-derived valuesare substantially smaller than those com-puted from the models. Part of this isprobably due to limitations in convertingfrom extinction to SAD using SAGE IIobservations (as discussed above) butmay be exacerbated in these comparisonsby deficiencies in the models’ lowerstratospheric size distribution.

ASAP Data Archive

Data sets that comprise the basis for thedata analysis will be archived at theSPARC Data Center (http://www.sparc.sunysb.edu/) including altitude/

latitude gridded fields of aerosol extinc-tion and derived quantities for the SAGEseries and HALOE. Data sets used in thetrend analysis will also be available atthis location. In addition, links to addi-tional sources of aerosol data that appearwithin this report will be included.Also, at least the SAGE data sets will beavailable remapped to equivalent lati-tude and potential temperature.

A final product that will be available is a‘gap filled’ data set for the period 1979through 2002 based on the SAGE record.Gaps exist between the June 1991 erup-tion of Mt. Pinatubo and the end of 1993due to instrument saturation andbetween November 1981 and October1984, when global space-based aerosolextinction measurements were not avai-lable. To fill the missing values, wehave used aerosol backscatter profilemeasurements from sites at Camaguey(Cuba), Mauna Loa, Hawaii (USA), andHampton, Virginia (USA) and backscat-ter sonde measurements from Lauder(New Zealand). This period encom-passes the El Chichon eruption and theonset of the Antarctic ozone hole and is,therefore, of particular interest.Beginning in April 1982 and through thebeginning of SAGE II observations in1984, we have used a composite of dataconsisting of SAM II, the NASA Langley48-inch lidar system, and lidar data fromthe NASA Langley Airborne LidarSystem. Data from this later data set hasonly been partially recovered for the1982 to 1984 period. Figure 5 (p. III)shows the stratospheric aerosol opticaldepth for the 1979-2002 period usingthe gap-filled data product. When moreof the airborne lidar data and particu-larly the revised aerosol product fromthe Solar Mesospheric Explorer (1981-1986) become available additional workon the El Chichon period will be pro-fitable.

References

Brock. C.A., et al., Particle formation in theupper tropical troposphere: A source ofnuclei for the stratospheric aerosol, Science,270, 1650-1653, 1995.

Deshler, T., et al., Thirty years of in situstratospheric aerosol size distribution mea-surements from Laramie, Wyoming (41N),using balloon-borne instruments, J. Geophys.Res., 108(D5), 4167, doi:10.1029/2002JD002514, 2003.

Hamill, P., et al., The life cycle of strato-spheric aerosol particles, Bull. Am. Meteorol.Soc., 78, 1395-1410, 1997.

Hervig, M.E., et al., Aerosol size distribu-tions obtained from HALOE spectral extinc-tion measurements, J. Geophys. Res., 103,1573-1583, 1998.

Hofmann, D.J. and T. Deshler, Stratosphericcloud observations during formation of theAntarctic ozone hole in 1989, J. Geophys.Res., 96, 2897-2912, 1991.

Rinsland, C.P., et al., H2SO4 photolysis: Asource of sulfur dioxide in the upper strato-sphere, Geophys. Res. Lett., 22, 1109-1112,1995.

Rosen, J.M., The vertical distribution of dust to30 km, J. Geophys. Res., 69, 4673- 4676, 1964.

Palmer, K. F. and D. Williams, Optical con-stants of sulfuric acid: Application to the cloudsof Venus?, Appl. Opt., 14, 208-219, 1975.

Tisdale, R.T., et al., Infrared optical con-stants of low-temperature H2SO4 solutionsrepresentative of stratospheric sulfateaerosols, J. Geophys. Res., 130, 25,353-25,370, 1998.

Thomason, L. W. and G. Taha, SAGE IIIAerosol Extinction Measurements: InitialResults, Geophys. Res. Lett., 30, 33-1 - 33-4,doi:10.1029/2003GL017317, 2003.

Thomason, L. W., et al., A comparison of thestratospheric aerosol background periods of1979 and 1989-1991, J. Geophys. Res., 102,3611-3616, 1997.

Trepte, C.R. and M. H. Hitchman, Tropicalstratospheric circulation deduced from satel-lite aerosol data, Nature, 355, 626-628, 1992.

Introduction

A prominent aspect of the observed cir-culation in the middle atmosphere is thevariance, with periods ranging from mi-nutes to tens of hours, that is most plausi-bly interpreted as resulting from upward-

This means that gravity waves that playonly an insignificant role in the tropo-sphere can grow to very large amplitudesat high altitudes. Gravity waves act toexchange mean momentum between thesurface and the atmosphere and amongdifferent layers of the atmosphere and, as

propagating internal gravity waveslargely forced in the troposphere. In theabsence of damping or strong basic-stateinhomogeneities, the amplitude of thegravity wave wind and temperature fluc-tuations will vary roughly as the recipro-cal of the square-root of mean density.

�

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such, are crucial in forcing the global-scale circulation in the stratosphere andmesosphere. Since the distribution ofmany trace constituents involved inozone chemistry is very strongly affectedby the atmospheric circulation, anunderstanding of gravity wave effects inthe middle atmosphere has become acentral issue for the practical problem ofmodelling stratospheric ozone. Much ofthe gravity wave variance (particularlyin the vertical velocity) occurs at hori-zontal scales too small to be explicitlyresolved in current General CirculationModels (GCMs) of the global atmo-sphere. The development and applica-tion of parameterisation schemes to ade-quately account for the effects ofunresolved gravity waves on the meanflow is now a prime consideration forgroups involved in numerical modellingof the middle atmosphere dynamics andchemistry.

SPARC has made gravity wave processesand parameterisation one of its focusareas, and SPARC co-sponsored animportant workshop in Santa Fe in 1996that brought together the gravity waveobservational and modelling communityand the global modelling community(SPARC Newsletter N° 7; Hamilton,1997). Recently SPARC co-sponsored anAGU Chapman Conference on “GravityWave Processes and Parameterisation”that addressed a range of key issues inthis area. The meeting was held inWaikoloa, Hawaii, USA, January 10-14,2004, and attracted 64 participants from11 countries. This paper summarisesjust a fraction of the many interestingposters and oral presentations, andbriefly discusses some of the majorissues raised at the meeting. Also note-worthy were outstanding overview talkson the middle atmospheric gravity waveproblem by R. Garcia and T. Dunkertonand on the oceanic gravity wave spec-trum by E. Kunze.

Observations

There have been some important deve-lopments in observational techniques inrecent years. A. Hertzog presented someresults from long-duration constant-density superpressure balloons. Heshowed that frequency spectra of thewinds following the balloon location - essentially the intrinsic spectrum - canbe computed for periods as short as 20minutes. Particularly exciting is the abi-lity to derive accurate vertical windvelocities at high sampling rates.Figure 1 shows a time series of the verti-cal flux of zonal momentum computedfrom the wind measurements from one

balloon as it drifted near the equator and19 km altitude (the winds were first fil-tered to include only fluctuations withperiods between 1 and 12 hours). Sincethe balloon drifts westward tens of thou-sands of km over the period shown, thevariation seen in the momentum fluxtime series reflects both temporal andspatial modulation of the gravity wavefield.

Another technique developed recently isthe use of satellite GPS tomography tomeasure vertical profiles of temperaturesin the stratosphere. The measurementscan be taken whenever paths betweentwo individual satellites happen to inter-sect the planetary limb, leading to awidely-scattered geographical coveragethat supplements the fixed station distri-bution typical for many other profilingmeasurements. T. Tsuda reviewedprogress so far on two GPS satellite mis-sions and showed that global maps ofwave temperature variance can be pro-duced. The upcoming US-Taiwan COSMIC and Brazilian EQUARS satellitemissions will provide a much denserdata coverage in the near future.

D. Wu presented results from an analysisof horizontal variations in UARSMicrowave Limb Sounder (MLS) dataand in operational Advanced MicrowaveSounding Unit (AMSU) data. These datacan provide information on long-verticalwavelength gravity waves in the middleatmosphere. He was able to relate thegeographical modulation seen in theMLS and AMSU variability to likely tro-pospheric sources. Particularly impres-sive were areas of enhanced variabilityabove regions of significant topography.

Detailed Modelling of Wave Dissipation

G. Klaassen reviewed the very signifi-cant progress in understanding the linearnormal mode instability of monochro-matic plane waves. The problem seemslargely solved for the case of no meanshear, and work is now focussing onextending the theory to treat more ge-neral mean states. U. Achatz described alinear approach based on identifying theoptimally growing structures rather thannormal modes.

D. Fritts described very fine resolutionnonlinear simulations of the single wavebreaking phenomenon. The initial evo-lution of simulated instabilities closelyresemble predictions from linear theory,but the nonlinear development leads to arange of interesting phenomena withimportant implications for parameterisa-tion of wave dissipation, as well as asso-ciated heat, momentum and constituenttransports. Some results suggest a ten-dency for instability to largely obliterateindividual waves rather than simply limiting their subsequent growth withheight.

Topographic Wave DragParameterisations

S. Webster reviewed recent progress inparameterising the effects of unresolvedtopographic effects on atmospheric flow.In the 1980’s the first simple parameteri-sations were devised based on (i) anassumption that all the topographic flow

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Figure 1. A time series of the product of zonal velocity and vertical pressure velocity froma balloon drifting at constant density (near 19 km altitude). The velocities have been band-passed to include only periods between 1 and 12 hours before the product is computed.[Provided by R. Vincent].

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perturbations project on to gravity waves,and (ii) idealised notions of wave ampli-tude saturation. The predictions of suchparameterisations have now been testedagainst explicit very-high resolutionregional models. It appears that the pre-dictions of the total surface topographicdrag is reasonably accurate, but that inreality much of the drag is likely attribu-table to “flow blocking”, meaning thatthe stress divergences should occur prin-cipally near the ground. So the simpleparameterisation schemes overestimatethe gravity wave stresses in the strato-sphere. This conclusion is supported byglobal model forecast experiments, wichsuggest that only modest topographicgravity wave drag is required in thelower stratosphere.

Basic Issues Concerning WaveEffects on the Mean Flow

There have been recent concerns aboutthe adequacy of the traditional paradigmfor treating gravity wave effects, i.e. that,in steady-state, waves transfer meanmomentum from the regions where theyare forced to the region where they aredissipated. New effects are introducedwhen waves refract in such a way thatthe wavevector at absorption is no longerparallel to that at forcing. O. Buhlerreviewed recent work on this subjectincluding some idealised calculations ofthe effects of a wave train that refracts asit propagates through the periphery of acircular vortex. Some of the wave rectifi-cation effects in this case are feltremotely by the vortex as a whole.C. Warner presented some preliminarycalculations that suggest that this effectmight plausibly be significant for gravitywaves propagating through the middleatmosphere, but much more work will benecessary to establish how large theeffect really is in practice.

Gravity WaveParameterisations

C. Hines discussed developments inDoppler-Spread Theory (DST) for gravitywaves. As originally advanced, the the-ory used heuristic arguments to deter-mine the effects of the nonlinear advec-tion terms from a spectrum ofvertically-propagating waves on the highvertical wavenumber tail of the spec-trum, all within an Eulerian framework.The result suggested that a saturated tailwith something close to the observed m-3

vertical wavenumber dependence shouldresult. In more recent work C. Hines hasre-examined the problem in a Lagrangian

framework in which the wave dynamicscan be treated approximately as linear.The result is a more rigorous derivationof the roughly m-3 dependence of the tail.C. Hines finds that these new develop-ments have only modest implications forthe practical Doppler-Spread Parameteri-sation (DSP) scheme that he had deve-loped earlier on the basis of the DST.

C. McLandress discussed a comparisonof the drag computed using the HinesDSP and the Warner-McIntyre parame-terisation (WMP) for particular examplemean flow profiles. The Warner-McIntyre scheme uses an empirically-based saturation condition that limitsthe energy in the tail of the spectrum.The momentum flux spectra imposednear the tropopause level was prescribedto be identical in the two schemes.There were systematic differencesbetween the performance of the twoschemes, with much more of the wavespectrum being removed lower down inthe atmosphere by the WMP than theDSP. The profiles of flux and flux diver-gence computed by the two schemesbecome similar when the saturationfluxes for the WMP are raised by a factorof 25 over their standard values.

An important development described inseveral talks at the workshop has beenthe systematic application of known constraints on the mean flow forcing toadjust aspects of parameterisations.J. Alexander presented calculations inwhich the input spectrum of momentumflux versus horizontal phase speed forthe Alexander-Dunkerton Parameterisa-tion (ADP) is adjusted to account for theneeded gravity wave mean-flow forcingin the middle atmosphere (determinedthrough analysis of large-scale observa-tions). The results were somewhat dif-ferent in midlatitudes and the tropics,with a broader phase speed spectrumindicated for low latitudes. D. Ortlanddiscussed a systematic approach to theinverse problem of finding input spectrain the ADP that can reproduce therequired wave drag as determined fromsimulations of the middle atmosphericcirculation obtained with a two-dimensional (zonally-averaged) model.

R. Vincent and P. Love discussed the useof mesospheric radar measurements ofthe winds near the equator to constrainthe tropospheric input spectra employedin a ray-tracing model (with sourcesassociated with regions of convection asseen in satellite imagery). It appears that,with appropriate assumptions about thesource spectra, much of the observedmean-flow forcing inferred from windobservations in the equatorial meso-

sphere can be explained by troposphericconvective sources.

One issue that is involved in such adjust-ment of parameterisations is the determi-nation of how much of the mean flowforcing is attributable to gravity wavesversus the motions that should beresolved in current climate models (orcurrent global observational analyses).This determination has typically beenbased on monthly-mean data used toinfer the Coriolis and advective effects ofthe residual mean meridional circulationalong with some other observational esti-mate for the contributions of planetarywaves. In principle, a more satisfyingapproach might be based on the analysisincrements obtained in data assimilationprocedures within a forecast-analysiscycle. W. Tan discussed this issue butnoted that the inadequacy of current datasources and assimilations may severelylimit the utility of this approach, at leastat present.

J. Beres discussed linear theory resultsfor the gravity wave field forced bylocalised transient heating. She thenused these results as the basis for a prac-tical scheme to determine the input spec-trum appropriate for convective forcing.Her approach basically takes the grid-scale latent forcing computed in the con-vective parameterisation and assumessome subgrid-scale structure for the heat-ing. Then the linear theory is used toobtain a source spectrum for the gravitywave parameterisation that depends onthe grid-scale heating and the resolvedhorizontal winds. This is a rational wayto begin to consider the effects of vari-ability of convection in the gravity waveparameterisation problem. J. Beres pre-sented some preliminary results obtainedwith the NCAR Whole AtmosphereCommunity Climate Model that incorpo-rated a version of the ADP with sourcespectra calculated with her scheme.

H.-Y. Chun discussed another paramete-risation for convective gravity waves thatalso related the source spectrum to grid-scale winds and convective heating. I.-S. Song discussed results with thissource spectrum determination incorpo-rated into Lindzen and Warner-McIntyreparameterisations.

Implementation ofParameterisations in Models

T. Shaw discussed the issue of how gra-vity wave drag parameterisations areaffected by the effective truncation of themodel domain at some finite altitude that

18

is inherent in the numericaldiscretisation. She showedthat the residual meridionalcirculation differs dramati-cally if the parameterisedgravity wave fluxes thatreach the model top areassumed to be absorbed atthe top level or are simplyneglected. It seems that, interms of simulating theresidual circulation, assum-ing that the flux is absorbedat the top will lead to a resultmuch closer to what wouldbe obtained by explicitlyincluding a very high modeldomain.

E. Manzini described therole of parameterised gravitywaves in the simulation ofthe near-mesopause circula-tion in the Max PlanckInstitute HAMMONIA cou-pled circulation-chemistryGCM. In particular, she investigated theissue of interhemispheric asymmetry insummer mesopause temperatures.M. Giorgetta discussed results with aversion of the ECHAM model showingthat a combination of resolved equatorialwaves and an appropriately tuned gra-vity wave parameterisation could allowthe model to produce a quite realisticquasi-biennial oscillation (QBO) of thetropical stratosphere. He then used themodel to investigate the effect of changedcarbon dioxide concentrations on theQBO.

Explicit Simulations of WaveForcing in Regional Models

A number of papers dealt with detailedsimulations of gravity wave generationand propagation in high-resolution li-mited-area models. T. Horinouchi dis-cussed 3D cloud-resolving simulationsof gravity waves forced by convection ina tropical squall line. He showed thatthe model can convincingly simulate theentire life cycle of convectively-forcedwaves: generation, propagation throughthe middle atmosphere, and nonlinearbreakdown near the mesopause. Heshowed that his simulated meteorologi-cal fields could be used as the basis for acalculation of airglow emission, thus,allowing a direct comparison of hismodel results near the mesopause withairglow imager observations.

The convection and convectively forcedgravity waves in springtime in northernAustralia were the subjects of the recent

Darwin Area Wave Experiment(DAWEX) field campaign. Two papersdealt with model studies of the convec-tively-generated gravity waves duringthis experiment. J. Alexander discussedthe wave field computed for one day inDAWEX using a dry model forced withtime-dependent, 3D heating fields basedon detailed meteorological radar observa-tions of precipitation. The radar can beexpected to give a good estimate of theoverall space-time evolution of the pat-tern of precipitation, but J. Alexandernotes some uncertainty in overall ampli-tudes. G. Stenchikov described a simu-lation of the circulation and convectionfor one day during DAWEX using a 3Dcloud-resolving mesoscale model.

T. Lane simulated isolated convectionand resultant stratospheric gravity wavesin a 2D version of a cloud-resolvingmodel. The restriction to 2D allowedhim to examine results obtained over arange of model grid resolutions. He findsthat the momentum flux spectrum of thewaves emerging into the stratosphereabove the convection depends signifi-cantly on model resolution even down torather fine grid spacings. Notably, con-vergence of results for the momentumflux occurs only when the horizontalgrid spacing is reduced substantiallybelow 1 km (which is typical of the hori-zontal resolution of most 3D models thathave been applied to this problem).

Z. Chen discussed the generation ofstratospheric gravity waves by atyphoon simulated in the MM5mesoscale model. He finds the typhoonacts as a strong source for relatively

large horizontal wavelengthwaves (~500-1000 km) andthat the features of the simu-lated stratospheric waveshave some similarity tothose seen in earlier aircraft,dropsonde and radar obser-vations in the vicinity oftropical cyclones.

F. Zhang discussed a drysimulation of a growing baro-clinic wave in a multiply-nested version of the MM5regional model. This multi-ple nesting allowed him toconsider motions from thecontinental scale down toquite small scales (his mostambitious experiment hadquadruple nesting and afinest grid with 3.3 km hori-zontal and 180 m verticalgrid spacing). He found thatthere was a very significantflux of gravity waves above

the jet exit region and that the waves haddominant horizontal wavelengths ofabout 150 km, vertical wavelengths ofabout 2.5 km, and intrinsic horizontalphase speeds of about 8 ms-1. Figure 2shows results from a triply-nested ver-sion of his model experiment. F. Zhangfound that a measure of the deviationfrom diagnostic dynamical (cyclo-strophic) balance in the jet-level flowprovides a good indication of the regionsof strong gravity wave generation.

Explicit Simulations of theMiddle Atmospheric GravityWave Field in Global Models

J. Scinocca discussed the role of moistprocesses in exciting the explicitly-resolved gravity (and equatorial plane-tary) waves in a global atmosphericGCM. He found that the assumptionoften made that waves are forcedprimarily by heating in the convectiveparameterisations may be somewhatover- simplified, and that there may be asignificant role for the large-scale con-densation heating as a wave excitationmechanism.

S. Watanabe discussed the middleatmospheric gravity wave field in aT106-L250 global GCM. He showedthat the model simulates a realistic m-3

vertical wavenumber spectrum. Hewent on to use the gravity wave proper-ties in the T106 model as the basis forspecifying the input spectrum in aHines parameterisation that was imple-mented in a T42 version of the model.

Figure 2. The 13-km pressure (thick blue line, every 2 hPa), horizon-tal divergence (thin blue line; solid, positive; dashed, negative;every 5x10-6 s-1) and wind vectors (maximum of 25 ms-1) simulatedfrom the triple-nested mesoscale model MM5 with horizontal (verti-cal) resolutions of 10 km (360 m). The wind speed at 8 km (near themaximum jet strength level) greater than 45ms-1 is shaded in blue(every 5 ms-1). The distance between tick marks is 300 km [adaptedfrom Figure 12d of Zhang (2004)].

19

Solar Variability and Climate: Selected Results from the SOLICE Project

J.D. Haigh, Imperial College London, UK (j.haigh@imperial.ac.uk)J. Austin, N. Butchart, M.-L. Chanin, S. Crooks, L.J. Gray, T. Halenka, J. Hampson,L.L. Hood, I.S.A. Isaksen, P. Keckhut, K. Labitzke, U. Langematz, K. Matthes, M. Palmer,B. Rognerud, K. Tourpali, C. Zerefos

K. Hamilton showed that the m-3 spec-trum appears in a very fine vertical reso-lution (L160) simulation with the GFDLSKYHI model. He also discussed initialresults with a global model of unprece-dented spatial resolution (T1279-L96)that has been developed and run at theEarth Simulator Center. He showed thatthe near-tropopause gravity wave field inthis model had encouragingly realisticfeatures, at least in terms of overall spaceand time variance spectra.

Summary

The essential problem behind the manyuncertainties in adequately treatinggravity wave effects is a lack of detailedempirical information about the gravitywave field in the middle atmosphere.While much progress has been made inobservational methods, each techniqueapplied has very significant limitationsin terms of geographical and temporalsampling, and in terms of the spatialwave scales that can be detected. Eventhe appropriate basic conceptual frame-work for understanding the middleatmospheric gravity wave field is notclearly determined from current obser-vations. It is conceivable that the fieldat any point may typically be domi-nated by quasi-monochromatic waves,

but the opposite view, in which a fully-developed broad spectrum of wavesdominates virtually everywhere, is alsopossible. It was apparent from the pre-sentations at the conference that theobservation of the m-3 dependence ofthe average vertical wavenumber spec-trum does not, by itself, clearly diffe-rentiate among various possible views of the basic physics of the wavefield.

A great deal of progress was reportedon practical parameterisations that canbe implemented in current models.The first generation of such parameteri-sations discussed at the Santa Fe work-shop typically made very simple andarbitrary assumptions about the sourcespectrum and its geographical and tem-poral variability. There has beenimportant progress towards more physically-based source spectra andtowards more systematic application ofobserved constraints to pin down theparameters employed.

Perhaps the most impressive recentprogress has been made using explicitlimited-area, high-resolution nonlinearsimulations of wave generation and dis-sipation. Since the Santa Fe workshopthere has been a major increase in acti-vity devoted to explicit simulation of

gravity waves forced by convection and other sources. In the case of topographically-forced gravity waves,results from limited-area simulationshave been used very successfully toredesign the gravity wave parameterisa-tions employed in global models. Forthe nonstationary wave field forced byconvection and other sources, the inter-action between detailed simulationsand design of practical parameterisa-tions is in a less-developed stage, butuseful progress has already been made.Similarly, the impressive explicit high-resolution simulations of wave breakingthat have been produced in recent yearswill ultimately have implications for thedesign of gravity wave parameterisations.

References

Zhang, F., 2004: Generation of mesoscalegravity waves in upper-tropospheric jet-front systems. J. Atmos. Sci., 61, 440-457.

Hamilton, K., editor, 1997: Gravity WaveProcesses: Their Parameterization in GlobalClimate Models. Springer-Verlag, 401 pp.

1. Introduction

The SOLICE (Solar Influences onClimate and the Environment) projectwas funded by the EuropeanCommunity Framework 5 programmewith the stated objectives:• To extract the stratospheric solar sig-nal in datasets of ozone, temperature,geopotential height, vorticity and cir-culation.• To assess the impacts of solar vari-ability in the troposphere.• To investigate the response of strato-spheric composition and climate tovariations in solar ultra-violet radia-

tion using General Circulation Models(GCMs), Coupled Chemistry-ClimateModels (CCMs), Chemical TransportModels (CTMs) and mechanistic models.• To develop a more complete under-standing of the mechanisms by whichsolar variability influences the naturalvariability of the stratosphere and tro-posphere.

The project, involving eight Europeaninstitutions and two American colla-borators, was initiated in April 2000and has recently been completed.Here we report on a selection of the

results. Full results and further pro-ject details are available athttp://www.imperial.ac.uk/research/spat/research/SOLICE/index.htm.

2. Solar signal in the middle atmosphere

2.1. Observations of temperature

The response of the middle atmo-sphere to solar variability has beenestimated from a variety of differentdatasets including lidar, rocketsonde,SSU/ MSU, FUB, as well as the NCEP

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Figure 1. Annual mean tem-perature response (K) to solaractivity (solar max – solarmin). Responses from rocketsondeobservations in: (a) Tropics (Ascension Island,8°S; and Kwajalein, 9°N); (b) Northern subtropics (BarkingSands, 22°N; Cape Kennedy,28°N; Point Mugu, 34°N); (c) mid, high-latitudes (Shemya,53°N; and Primrose Lake, 55°N). Dotted and dashed lines indi-cate 1 and 2 sigma error bars.The solar response is given fora full solar cycle having amean amplitude of the solarforcing estimated from the lastthree cycles [from Keckhut etal., 2004].

and ERA-40 re-analyses. Here we pre-sent some of the results found byapplication of a multi-parameterregression analysis using the 11-yearsolar cycle (represented by the 10.7 cmflux) and a Quasi Biennial Oscillation(QBO) signature, all superposed on atrend which is assumed to be linear.Volcanic effects are dealt with either

by inclusion of a stratospheric aerosolindex or by removing data for the twoyears following major eruptions.Figure 1 shows the annual mean signalfrom rocketsonde data (1969-early1990s) grouped into three latitudebands. Figure 2(a) presents the analy-sis of zonal mean SSU satellite data, asanalysed by J. Nash (see Ramaswamy

et al, 2001) andcompleted downinto the LowerStratosphere (LS)by MSU andFigure 2(b) thesame from ERA-40. It is to be no-ted that in ERA-40, the TOVS,ATOVS and SSUinstruments areused as radiancesin the data assi-milation. Up toabout 10 hPa,radiosonde data

is used in the data assimi-lation to bias correct allinstruments but above thisheight the model has noother reference. However,for the recent period,AMSU-A channel 14 wasused as reference to adjustSSU channels 2 and 3 witha fixed offset.

In all the datasets one candistinguish in the strato-sphere three types ofbehaviour: the tropicalregion with a positiveresponse of +1 to 2 K ma-ximising just below thestratopause, a subtropicalregion indicating a muchless significant response,but still positive, and a

mid-latitude response which is nega-tive. Seasonal analysis (not shown)reveals that the latter is determined by alarge negative response in winter domi-nating a smaller positive summer signal.

There is more uncertainty in the verti-cal profile of the temperatureresponse. In the tropical (25°S-25°N)LS a warming of 0.70 ± 0.18 K fromminimum to maximum was found byHood and Soukharev (2000) in MSUchannel 4 data. The ERA-40 Re-analy-sis also shows a lower stratosphericsignal maximizing near 20 to 30degrees latitude in both hemispheresand near the 30 hPa level and a similarresponse is found in NCEP data (seeFigures 7 p. III and 11 p. 27). TheSSU and ERA-40 results, however,show significant disagreement withthe latter presenting a local minimumat 10-20 hPa and the former suggestinga negative response around 50hPa.The reasons for these disagreementsremain uncertain.

Observations of ozone

The amplitude of the solar signal inozone has been investigated in observa-tions from all available sources, namely:ground based (total column ozone, pro-file from Umkehr measurements),

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in situ measurements (ozonesonde profiles) and satelliteobservations.

Sixteen stations measuringthe vertical distribution ofozone with the Umkehrmethod were considered,but quality checks suggested that only four NorthernHemisphere (NH) stationslocated between 19 and47°N during the period1957-2001 would qualify forthe present analysis. Theseare Mauna Loa (20°N),Tateno (36°N), Boulder(40°N) and Arosa (47°N).Results are presented inFigure 3(a) for the period1985-2002 (to make themcomparable with the SAGEanalysis) and generallyshow a positive response inthe LS. Results from ozonesondes (not shown) are ge-nerally not statistically dis-tinguishable from zero.

Ozone data in the form ofozone mixing ratio werederived from SAGE II (ver-sion 6.1) data, updatedthrough June 2002 (end ofthe record), and used toconstruct 10° latitude beltsfrom 60°S to 60°N. Eventhough the original datawere retrieved from groundlevel up to the altitude of 70 km, the many missingdata values and the volcanicaerosol data contaminationforce us to restrict the analy-sis to the range of altitudesfrom 20 – 50 km. Figure3(b) shows higher ozone inthe solar maximum phase,significant at altitudes from35 – 45 km at all latitudes.Positive signals also extendto lower altitudes at mid-latitudes. This latter resultis seen also in the ozonesonde, as well as theUmkehr profile analysis atthe stations of Arosa andBoulder, where the solarcycle signal becomes posi-tive and significant at alti-tudes above about 20 km.

Although the largest percent-age ozone changes over asolar cycle occur in theupper stratosphere, the corre-sponding column amounts

are too small to explain theobserved solar cycle varia-tion of total ozone, which isseveral per cent, dependingon latitude and season(Hood, 2004). Therefore, theobserved lower stratosphericpositive ozone response islikely to dominate the totalozone solar cycle variation atall latitudes. Solar cycle vari-ation is the largest singleform of long-term variabilityfor ozone in the tropics andsubtropics.

2.3. Coupled chemistry-climate

simulations

Model calculations havebeen performed with fourmodels: two coupled che-mistry-climate models byUKMO (UMETRAC, seeAustin and Butchart, 2003)and FUB (FUB-CMAM-CHEM, see Pawson et al.,1998; Steil et al., 1998;Langematz, 2000), one chem-ical transport model by UIO(SCTM-1, see Rummukainenet al., 1999), and one 3Dmechanistic model by CNRS(MSDOL, developed byService d’Aéronomie fromthe ROSE model).

The relative importance ofdynamics and photoche-mistry in determining theozone response have beenstudied with SCTM-1.Figure 4(a) shows the resultsof changing the prescribeddynamical fields, accordingto the results of the BerlinGCM for the 11-year cycleresponse, without anychanges in UV. This leadsgenerally to an increase in ozone but with largedecreases over the polarregions. Because of the largevariability in high latitudesthese changes are not statisti-cally significant, but thetropical and sub-tropicalincreases in the LS are over6%. The impact on ozone ofsolar UV changes alonepeaks at just over 3% asshown in Figure 4(b), andare similar to the ozonechanges previously calcu-lated by 2D models (e.g.Haigh, 1994). The net effect

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of dynamical and chemical changes isdominated by the dynamical changesin the LS and also in the upper strato-sphere at high latitudes.

The coupled chemistry GCM ozoneresponses are shown in Figure 5,which shows the differences betweensteady state responses to solar maxi-mum and solar minimum conditions(each run of several decades). UME-TRAC and SCTM-1, like other previ-ous investigations (see review byShindell et al., 1999) com-pare poorly with observa-tions, indicating insufficientozone increase in thestratosphere and do notshow the negative featureindicated in the observa-tions in the LS (see aboveand Hood, 2004). In con-trast, the FUB-CMAM-CHEMresults compare favourablywith observations in show-ing these two important fea-tures. It is likely, therefore,that some physical or che-mical processes are missingfrom these other modelsthat are present in FUB-CMAM-CHEM. The meso-spheric ozone decrease inFUB-CMAM-CHEM resultsfrom enhanced catalyticdestruction by HOx, whichis produced by enhancedLyman-α irradiance duringsolar maximum. The shapeand magnitude of the mid-dle stratospheric ozoneincrease indicate an ozoneresponse to the weaker ther-mospheric NOx source in

solar maximum, while the lowerstratospheric ozone decrease is a com-bined effect of stronger chemical anddynamical ozone destruction in solarmaximum (Langematz et al., 2004).This is due to an additional source ofNOx in the polar regions at the top ofthe model putatively due to EnergeticElectron Precipitation (EEP), which isepisodic but occurs more frequentlyduring solar minimum. This decreasesozone during solar minimum abovethe mixing ratio peak and leads to a

‘self healing effect’ causing moreozone to be produced in the LS fromthe increased penetration of UV.Hence, the difference in ozone fromsolar minimum to solar maximumwould be a larger increase in the upperstratosphere and a decrease in ozonein the LS relative to what would occurwithout the NOx process included.This hypothesis has been put forwardpreviously using 2-D models (Callis etal., 2001) but SOLICE is the firstattempt to simulate these processes in

a CCM. Several problemsremain with regards tospecifying the magnitude ofthe NOx source and itstransport from the uppermesosphere to the upperstratosphere. The FUB-CMAM-CHEM results sug-gest that it can be important,but further calculationsneed now to be made toconfirm these findings.

Figure 6 shows the annualmean temperature changebetween solar minimumand maximum from thetwo CCM studies. Themodelled impact generally

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increases with altitude fromthe LS to about 1 hPa. Theyare in reasonable agreementwith observations in the mid-dle and upper stratosphere,however, the models are notable to capture the secondarymaximum in the observedtemperature signal in the LS.The fields are somewhat noisydespite the long duration ofthe integrations, with the last10 years (UMETRAC) or 14years (FUB) analysed here.Part of this noise in UME-TRAC is due to the presenceof a QBO in the model; QBOeffects are discussed furtherbelow. The lower strato-spheric cooling shown byFUB-CMAM-CHEM is uniquecompared to other CCM simu-lations, and is due partially tochanged chemical processesand partially due to less radia-tion coming from above (‘selfhealing effect’), as discussedabove.

For the MSDOL simulations(CNRS, not shown) it wasfound that the level of lower-boundary wave-forcing in themodel significantly affectedthe solar signal seen in thesimulations. The use of climatologi-cally averaged lower boundary forcingreduces the amount of wave forcing inthe model. It was found that a prefe-rential amplitude of forcing, equiva-lent to a magnification of 1.8 of the climatological value (assumed inde-pendent of solar variability), allowedmaximum solar response. It was alsofound that, comparable to the solar sig-nal in rocketsonde data, there was sig-nificant longitudinal variation in thesolar response, particularly in the NHwinter, emphasising the importance ofzonal asymmetry in the solar response,and the fact that the longitudinal posi-tion must be taken into account whencomparing observational data betweenthemselves and with models(Hampson et al., 2004).

3. Interaction of the solar and QBO influences

3.1. Observations

Several publications (e.g., Labitzke,1987, 2002; Labitzke and van Loon,1988, 2000; van Loon and Labitzke,2000) have shown that during thenorthern winters the signal of the solarcycle below 10 hPa emerges more

clearly if the data are grouped accord-ing to the different phases of the QBO.This result was confirmed by Salbyand Callaghan (2003) who defined fortheir study the northern winter periodfrom September till February. It wasshown further that duringJanuary/February, i.e. during thesouthern summers, the influence ofthe QBO is also large over theSouthern Hemisphere (SH) (Labitzke,2002). A summary of current ideasexplaining the observed solar signal inthe stratosphere is given in Kodera andKuroda (2002), with emphasis on thedynamics over high latitudes duringwinter.

Here this work is extended to NHsummer; during July and August theSH is relatively undisturbed by plane-tary wave activity and the solar signalcan be found then relatively unob-scured by dynamical interactions.The NCEP/NCAR re-analyses are usedfor the period 1968-2002. The dataare grouped into years when the QBOin the LS (about 45 hPa) was in itswest phase and years when it was inits east phase, and our approach is touse a simple linear regressionbetween temperature and 10.7 cmsolar flux.

The vertical and meri-dional structure of thecorrelations between thesolar cycle and the zonalmean temperatures from1000 to 10 hPa is shownin Figure 7 (p. III) forJuly together with therespective temperaturedifferences betweensolar maxima and min-ima (taken to be 130 in10.7 cm units). Overmost of the Northern(summer) Hemisphere,extending to 30°S, thecorrelations (and tem-perature differences) arepositive for the unsorteddata. It is obvious, how-ever, that the largestsolar signal evolves forthe data in the eastphase of the QBO (mid-dle panels). Here, thecorrelations above 0.5cover a large height/lati-tude range. In the areaswith large positive corre-lations/temperature dif-ferences one can assumeadiabatic warm tropicsand sub-tropics. Thelargest temperature dif-ference, up to 2.5K are

found at the 100 hPa level over theequator, that is around the tropicaltropopause. Here, reduced strato-spheric upwelling leads to a warmingand lowering of the tropopause, e.g.Shepherd (2002). This hints to a con-nection to the meridional circulationsystems (Hadley circulation in the tro-posphere and Brewer - Dobson circula-tion in the stratosphere) as suggestedby Labitzke and van Loon (1995),Haigh (1996), Kodera and Kuroda(2002), and Salby and Callaghan(2003).

The latitudinal distribution of the tem-perature and geopotential height solarsignals has also been studied (notshown) and is found to be zonallyfairly uniform. At 30 hPa in Julywarming is seen at all longitudesnorthward of 30°S with much strongermagnitudes during the QBO eastphase. This is illustrated in Figure 8,which shows scatter plots of 30 hPatemperature against solar flux at twodifferent locations (one in the summerand one in the winter hemisphere), ineach case sorted into QBO east andwest phases. In the east phase correla-tions exceed 90 % at both sites but inthe west phase any relationship is veryweak.

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3.2. Mechanistic model studies

Direct solar heating of the atmospherecannot explain the temperatureresponse and its interaction with theQBO described in the previous sec-tion. A possible mechanism for thepenetration of the solar signal, at leastas far as the LS, is that the solar tem-perature response influences the zonalwind distribution (through thermalwind balance) and the altered winddistribution then influences the pro-pagation of planetary waves throughthe stratosphere (Kodera and Kuroda,2002; Hood, 2004).

Planetary wave forcing is known to bethe precursor to Sudden StratosphericWarmings (SSWs). Although SSWsare initiated at stratopause level, asthey mature they extend verticallythroughout the depth of the strato-sphere and are, thus, an ideal vehiclefor transferring a signal from thestratopause down into the lowest partof the stratosphere. Although theplanetary wave propagation influencewas proposed many years ago, theexact mechanism of this influence isstill not understood very well. Theinfluence mechanism is similar to thatproposed for the QBO (Holton andTan, 1980; 1982), in which the eastphase of the QBO in the LS confinesthe planetary waves to high latitudesand, hence, they have greater impacton the polar vortex than during thewest phase QBO. However, there is aconceptual problem with linking themechanisms of influence, since theQBO is primarily a feature of thelower equatorial stratosphere, whereasthe primary solar temperatureresponse is in the upper equatorialstratosphere.

The UK Met Office StratosphereMesosphere Model (SMM) has beenused to investigate the sensitivity ofthe modelled SSWs to zonal windanomalies associated with the 11-yearsolar cycle and the QBO. Initialexperiments (Gray et al., 2003)showed that increasing the planetary

wave forcing resulted in ear-lier warmings and that wheneasterlies were imposed atthe equator (at all heights)the warmings occurred ear-lier than when westerlieswere imposed. In a secondstudy (Gray, 2003), the SSWswere shown to be influencedby the winds in the LS, inagreement with the Holton-Tan mechanism, but theywere even more sensitive tothe imposed equatorialwinds in the upper strato-sphere. This is precisely theheight region in which thesolar influence is greatest,which suggests the possibi-lity that the upper equatorialstratopause regions is wherethe solar and QBO influ-ences interact. The observedamplitudes of the QBO andsolar cycle wind anomaliesat this level are also similar.

Figure 9. Ensemble of time-series of area-weighted, zonally-averaged modelled tempe-ratures (K) north of 62.5°N, at 32 km from the subtropical east-erly experiment (top) and thecontrol experiment (bottom).

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25

However, the wind anomalies associ-ated with the 11-year solar cycle arenot located directly over the equatorbut are found near the subtropicalstratopause region. Further modelexperiments were carried out (Gray etal., 2004) in which an easterly anoma-ly (representing solar minimum con-ditions) was imposed in the subtropicsbetween 40-50 km. It was imposedonly for the first 60 days, to mimic anearly winter anomaly. Figure 9 showsthe evolution of north polar tempera-tures from this experiment. The 20ensembles of the control run showconsiderable spread in the timing ofthe SSWs, with most of the warmingsoccurring around day 120. However,when the subtropical easterly anomalyis imposed, the timing of the warmingshows much less variability and theyoccur at least 20 days earlier at day100. The main result of these experi-ments is that the solar-induced windanomaly in the subtropical upperstratosphere and the QBO-inducedwind anomaly in the equatorial upperstratosphere can influence the timingof SSWs. The results suggest thatunder solar minimum conditions, withan easterly anomaly in the subtropicalupper stratosphere, warmings arelikely to occur earlier than in solarmaximum conditions. Similarly,warmings are likely to occur earlier inQBO/E than in QBO/W years.

A proposed mechanism for the interac-tion of the solar signal and QBO hasbeen suggested, based on these results(Gray et al., 2004). When the easterlyanomalies associated with solar mini-mum and QBO/E reinforce each other,the warmings will speed up and occurin early-to-mid winter. When thewesterly anomalies associated withsolar maximum and QBO/W reinforceeach other, the warmings will beslowed down but will, nevertheless,take place (unless they are sloweddown so much as to prevent theiroccurrence before the end of winter).Thus, in both Smin/E years andSmax/W years there will be a clearsolar/QBO signal. However, in theother combinations Smin/W andSmax/E the anomalies will partiallycancel and, hence, there is less likelyto be a clear solar/QBO signal inSSWs. This may help to understandthe puzzling observation that SSWsoccur in Smax/W years even thoughthe QBO/W phase means that there isno waveguide in the LS in those years.

The modulation of the timing of SSWsby the 11-year solar cycle and the QBOwill also modulate the strength of the

meridional circulation. This, in turn,will modulate the strength of up-welling in the equatorial LS. This mayhelp to explain the observed solar tem-perature response in the subtropicalLS in Figure 2a in both summer andwinter hemispheres since it will mo-dulate the speed at which the QBOdescends through this region of theatmosphere. The meridional patternof the two subtropical lower strato-spheric signals looks remarkably likethe QBO temperature response. It mayalso explain other observations (e.g.Salby and Callaghan, 2000), whichshow a solar modulation of the lengthof the westerly QBO phase.

3.3. GCM simulations

In the long-term mean state manyGCMs, including FUB-CMAM, are notable to reproduce a realistic QBO (e.g.,Pawson et al., 2000), so to simulate itseffect zonal wind anomalies are pre-scribed over the equator. Solar experi-ments with prescribed solar UV andozone changes were carried out in theFUB-CMAM with artificially imposedQBO westerlies only in the LS. Theseexperiments failed to reproduce theobserved relationship between thesolar and the QBO signals. Therefore,further experiments were performed inwhich rocketsonde data from Gray etal. (2001) were used to impose a QBOsignal not only in the LS but also inthe upper stratosphere. These modelexperiments with the FUB-CMAMhave confirmed for the first time witha GCM the results of recent observa-tional and Rutherford AppletonLaboratory (RAL) mechanistic modelstudies discussed above (Matthes etal., 2004). By imposing more realisticequatorial winds throughout thestratosphere, the model produces animproved simulation of the polar nightjet (PNJ) and mean meridional circula-tion (MMC) response to solar cyclevariations. The model results are nowin good agreement with observationaldata (Kodera and Kuroda, 2002; Hood,2004). Figure 10 shows the polewarddownward movement of the meanzonal mean wind differences betweensolar maximum and minimum forQBO easterlies (Figure 10a) and QBOwesterlies (Figure 10b) which was notproduced previously (Matthes et al.,2003).

The results indicate that the QBOdetermines the timing, rather than theexistence, of the solar signal.Stratospheric warmings during thewesterly phase of the QBO and duringsolar maximum years occur already in

January, whereas they appear onemonth later for the easterly phase. TheHolton and Tan relationship is evidentduring solar minimum years, whereasit is less clear for the solar maximumexperiments in agreement with obser-vations.

Experiments with the Met OfficeUnified model (not shown) also con-firm that equatorial stratospheric windanomalies associated with the QBOand solar cycle can interact to influ-ence the development of the winter-time circulation at higher latitudes(Palmer and Gray, 2004).

4. Solar influencein the troposphere

4.1. Observations

A multiple regression analysis of zonalmean temperature data from theNCEP/NCAR reanalysis dataset (usingdata from 1979 only as the lowerstratospheric data are suspect beforethat date) has been carried out (Haigh, 2003). The analysis incorporated anautoregressive noise model of orderone and eleven indices: a constant, alinear trend, the solar 10.7 cm flux, the QBO, the El Niño-SouthernOscillation, stratospheric aerosol loading (related to volcanic eruptions),North Atlantic Oscillation (NAO) andfour indices representing the ampli-tude and phase of the annual andsemi-annual cycles. Figure 11a showsa strong cooling trend in the stratosphereand warming in the troposphere inmid-latitudes. The solar signal ispresented in Figure 11b with warmingin the tropical LS at higher levels ofsolar activity extending in verticalbands into the troposphere in bothhemispheres at latitudes 20°-60°. It isinteresting to note that, while thestratospheric signal is similar to thatshown by Labitzke (2003) using a sin-gle parameter regression on detrendeddata (see Figure 6) the troposphericpattern is not the same and the solarresponse in the troposphere is gene-rally deduced to be larger when theother factors (QBO, ENSO etc) aretaken into account in a multipleregression. Care has to be taken whencomparing Figure 6, which is for July,with Figure 10, representing an annualmean but both results are broadly con-sistent with the solar signal of ~0.4 Kshown in the NH upper tropospheretemperatures in July and August byvan Loon and Shea (1999). The effectsof the QBO (Figure 11c) are largelyconfined to the tropical LS, while the

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ENSO signal (Figure 11d) is seenclearly throughout the tropics.Volcanic eruptions cause the strato-sphere to warm and the troposphere tocool (Figure 11e), while the NAO sig-nal (Figure 11f) is mainly confined toNH mid-latitudes.

A similar multiple regression analysisof zonal mean zonal wind data fromthe NCEP/NCAR re-analysis has beencarried out; some of the results areshown in Figure 12. These observa-tions show that the sub-tropical jetsare weaker and further poleward atsolar maximum than at solar mini-mum. It is worth noting that the hemi-spheric symmetry in the solar plot pro-vides further support for therobustness of the signal (the values ateach point being derived indepen-dently) and that the solar and NAOsignals are independent. If the sun isinfluencing the NAO, then some of theNAO signal in Figures 10,11 may beascribed to the sun – but not viceversa.

4.2. Simplified GCM experiments

Experiments with full GCMs (Haigh,1996, 1999; Larkin et al., 2000; FUB-CMAM, this project) have sug-gested that the response in the tropo-sphere is a weakening and polewardshift of the sub-tropical jets and aweakening and expansion of theHadley cells at solar maximum rela-tive to solar minimum. This pattern isremarkably similar to that resultingfrom the multiple regression study ofzonal winds presented in section 4.1and of vertical velocities by Gleisnerand Thejll (2003). These models allused fixed sea surface temperatures sothe influence must be induced by thedirect solar effects in the strato-sphere.

The simplest explanation for thisbehaviour is that the increase in staticstability induced by the stratosphericheating reduces vertical velocities inthe tropics and, thus, weakens theHadley circulations. This is a plausible

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Figure 11. Amplitudes of the componentsof variability in NCEP (1979-2000) zonalmean temperature due to: (a) trend (b)solar, (c) QBO, (d) ENSO, (e) volcanoes, (f) NAO. The units are K/decade for thetrend, otherwise maximum variation (K)over the data period. Shaded areas are notstatistically significant at the 95 % levelusing a Student’s t test. From Haigh, 2003.

first step but does not explain theHadley cell expansions nor the jetstream shifts.

The direct solar heating of the tropicallower stratospheric may be enhancedby changes in the mean circulation ofthe middle atmosphere induced bymodulation of planetary wave propa-gation, as discussed in section 2, andit seems clear that these effects areimportant in determining theQBO/solar interaction. However, theGCM used in the original demonstra-tion of the impact of solar UV variabi-lity on the troposphere (Haigh, 1996)only extended to 10 hPa and theLarkin et al. (2000) model, whichshowed the effects on troposphericwinds and circulation throughout theyear, extended only to 0.1 hPa so itappears that, at least for the tropo-spheric effects discussed in section4.1, a full simulation of the middleatmosphere is not necessary.

In order to understand the mecha-nisms underlying the observed tropo-spheric variability associated withsolar and volcanic forcing, we haveperformed some idealised-forcingexperiments using a simplified GlobalCirculation Model (sGCM) (Haigh etal., 2004), which includes full dynamicsbut temperature is relaxed towards a zonally symmetric equilibrium dis-tribution. Experiments with themodel have been designed to investi-gate the effects of perturbations to thetemperature structure of the LS byvarying the values used for the radia-tive equilibrium temperatures in theLS. Experiment U5 prescribes a uni-form increase of 5 K throughout thestratosphere, while in experiment E5the equatorial stratosphere is warmedby 5 K but this is gradually reduced tozero increase at the poles. The zonalmean zonal wind field found in thetwo sGCM experiments are presentedin Figure 13, each overlaid on the con-trol field. Run U5 shows a weakeningof the jet and a large equatorwardshift, while the response of experi-ment E5 is a weakening and latitudi-nal expansion, but mainly poleward

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shift, of the jets. The patterns are,thus, qualitatively similar to the vol-canic and solar signals, respectively,found in the multiple regressionanalysis of NCEP data (Figure 11).

The experiments with the sGCM pro-vide some indications as to how theseresponses arise. All runs (includingseveral not shown) in which thermalperturbations were applied only in theLS show effects throughout the tropo-sphere, with the vertically bandedanomalies in temperature and zonalwind typical of the results of the dataanalysis, and changes in the tropo-spheric mean circulation. Heating theLS increases the static stability in thisregion, lowers the tropopause andreduces the wave fluxes here. Thisleads to coherent changes through thedepth of the troposphere, involvingthe location and width of the jet-stream, storm-track and eddy-inducedmeridional circulation.

The precise shape of the patterns ofresponse depends on the distributionof the stratospheric heating perturba-tion: heating at mid- to high latitudescauses the jets to move equatorwardsand the Hadley cells to shrink, whileheating only at low latitudes results ina poleward shift of the jets and anexpansion of the Hadley cells. We,therefore, suggest that the observedclimate response to solar variability isbrought about by a dynamicalresponse in the troposphere to heatingpredominantly in the stratosphere.The effect is small, and frequentlymasked by other factors, but not negli-gible in the context of the detectionand attribution of climate change. Theresults, of both the sGCMs and fullGCMs, also suggest that at the Earth’ssurface the climatic effects of solarvariability will be most easily detectedin the sub-tropics and mid-latitudes.

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29

References

Austin, J. and N. Butchart, Coupled chemistry-climate model simulations forthe period 1980 to 2020: Ozone depletionand the start of ozone recovery, Q.J. Roy.Meteorol. Soc., 129, 3225-3249, 2003.

Callis, L.B., et al., Solar-atmosphere cou-pling by electrons (SOLACE), 3, Com-parisons of simulations and observations,1979-1997, issues and implications, J.Geophys. Res., 106, 7523-7539, 2001.

Gleisner, H. and P. Thejll, Patterns of tropo-spheric response to solar variability.Geophys.Res.Lett., 30, 1711, doi: 10.1029/2003GL017129, 2003.

Gray, L.J., The Influence of the equatorialupper stratosphere on stratospheric suddenwarmings. Geophys. Res. Letts. 30(4) doi:10.1029/2002GL016430, 2003.

Gray, L.J., et al., Solar and QBO influenceson the timing of stratospheric warmings. J. Atmos. Sci., submitted, 2004.

Gray, L.J., et al., On the interannual vari-ability of the Northern Hemisphere strato-spheric winter circulation: The role of theQBO. Quart. J. Roy. Meteorol. Soc. 127,1413-1432, 2001.

Gray, L.J., et al., The influence of the equa-torial upper stratosphere on NorthernHemisphere stratospheric sudden warm-ings. Quart. J. Roy. Meteorol. Soc. 127,1985-2003, 2003.

Haigh, J.D., The role of stratospheric ozonein modulating the solar radiative forcing ofclimate, Nature, 370, 544-546, 1994.

Haigh, J.D., The impact of solar variabilityon climate. Science, 272, 981-984, 1996.

Haigh, J.D., A GCM study of climate changein response to the 11-year solar cycle.Quart.J. Roy.Meteorol.Soc., 125, 871-892,1999.

Haigh, J.D., The effects of solar variabilityon the Earth’s climate. Phil. Trans. Roy.Soc. 361, 95-111, 2003.

Haigh, J.D., et al., The response of tropo-spheric circulation to perturbations inlower stratospheric temperature. Submittedto J. Clim, 2004.

Hampson, J., et al., The 11-year Solar-CycleEffects on the Temperature in the Upper-Stratosphere and Mesosphere: Part IINumerical Simulations and the Role ofPlanetary Waves. Submitted to J. Atmos.Sol.-Terrest. Phys., 2004.

Holton, J.R. and H.C. Tan, The influence ofthe equatorial quasi-biennial oscillation onthe global circulation at 50 mb., J. Atmos.Sci., 37, 2200-2208, 1980.

Holton, J.R. and H.C. Tan, The quasi-bien-nial oscillation in the Northern Hemispherelower stratosphere, J. Meteor. Soc. Jpn., 60,140-148, 1982.

Hood, L.L., Effects of solar UV variabilityon the stratosphere, In “Solar variabilityand its effect on the Earth’s atmosphere andclimate system”, AGU Monograph Series,Eds. J. Pap et al., American GeophysicalUnion, Washington D.C., in press, 2004.

Hood, L.L. and B.E. Soukharev, The solarcomponent of long-term stratospheric vari-

stratospheric chemistry simulations: Modeldescription and first results. J. Geophys.Res., 104, 26437-26456, 1999.

Salby, M. and P. Callaghan, Connectionbetween the solar cycle and the QBO: Themissing link. J. Clim., 13, 2652—2662,2000.

Salby, M. and P. Callaghan, Evidence of thesolar cycle in the general circulation of thestratosphere. J. Clim., 17, 34-46, 2004.

Shepherd, T.G., Issues in stratosphere-troposphere coupling. J. Met. Soc. Japan,80, 769-792, 2002.

Shindell, D., et al., Solar cycle variability,ozone and climate, Science, 284, 305-308,1999.

Steil B, et al., Development of a chemistrymodule for GCMs: first results of a multian-nual integration. Annal.Geophys. 16, 205-228, 1998.

Van Loon, H. and K. Labitzke, TheInfluence of the 11-Year Solar Cycle on theStratosphere Below 30km: a Review. SpaceSci. Rev. 94, 259-278, 2000.

Van Loon, H. and D. Shea, A probable sig-nal of the 11-year solar cycle in the tropo-sphere of the Northern Hemisphere.Geophys.Res.Lett., 26, 2893-2896, 1999.

�

ability : observations, model comparisons,and possible mechanisms. Proc. 2nd SPARCGeneral Assembly, Mar del Plata,Argentina, 2000.

Keckhut P, et al., The 11-year Solar-CycleEffects on the Temperature in the Upper-Stratosphere and Mesosphere: Part IAssessments of observations. Submitted toJ. Atmos. Sol.-Terrest. Phys., 2004.

Kodera, K., and Y. Kuroda, Dynamicalresponse to the solar cycle, J. Geophys.Res., 107, 4749, 2002.

Labitzke, K., Sunspots, the QBO, and thestratospheric temperature in the north polarregion. Geophys. Res. Lett., 14, 535-537,1987.

Labitzke, K., The Solar Signal of the 11-yearsunspot cycle in the stratosphere:Differences between the Northern andSouthern summers, J. Meteorol. Soc. Japan.80, 963-971, 2002.

Labitzke, K. and H. van Loon, Associationsbetween the 11-year solar cycle, the QBOand the atmosphere. Part I: The troposphereand stratosphere in the NorthernHemisphere winter. J.A.T.P., 50, 197-206,1988.

Labitzke, K. and H. van Loon, Connectionbetween the troposphere and the strato-sphere on a decadal scale. Tellus, 47 A,275-286, 1995.

Labitzke, K. and H. van Loon, The QBOeffect on the global stratosphere in north-ern winter. J.A.S.-T.P., 62, 621-628, 2000.

Langematz, U., An estimate of the impact ofobserved ozone losses on stratospheric tem-perature. Geophys. Res. Lett., 27, 2077-2080, 2000.

Langematz, U., et al., Chemical effects in11-year solar cycle simulations with theFreie Universität Berlin Climate MiddleAtmosphere Model with online chemistry(FUB-CMAM-CHEM), in preparation, 2004.

Larkin A., et al., The effect of solar UV irra-diance variations on the Earth’s atmo-sphere. Space Sci.Rev., 94, 199-214, 2000.

Matthes, K., et al., GRIPS solar experimentsintercomparison project: initial results,Meteorology and Geophysics. 54, 71-90,2003.

Matthes, K., et al., Improved 11-Year SolarSignal in the Freie Universität BerlinClimate Middle Atmosphere Model. J.Geophys. Res. doi:10.1029/2003JD004012,2004.

Palmer, M.A. and L.J. Gray, Modelling theresponse to solar forcing with a realisticQBO. In preparation, 2004.

Pawson, S., et al., The GCM-Reality Inter-comparison Project for SPARC (GRIPS):Scientific issues and initial results, Bull.Am. Meteorol. Soc., 81, 781-796, 2000.

Pawson, S., et al., The Berlin troposphere-stratosphere-mesosphere GCM: Sensitivityto physical parametrizations, Q. J. R.,Meteorol. Soc., 124, 1343-1371, 1998.

Ramaswamy, V., et al., Stratospheric tempe-rature trends: observations and model simula-tions, Rev. Geophys., 39, 71-122, 2001.

Rummukainen, M., et al., A global modeltool for three-dimensional multiyear

30

Report on the “International Workshop on CriticalEvaluation of millimeter-/sub-millimeter-wave

Spectroscopic Data for AtmosphericObservations”

Ibaraki University, Mito, Japan 29-30 January 2004 Yasuko Kasai, Communications Research Laboratory, Japan (ykasai@crl.go.jp)Takayoshi Amano, Ibaraki University, Japan (amano@mx.ibaraki.ac.jp)

Introduction

Microwave remote sensing measure-ments have played an important roleas a probe into understanding the che-mistry and physics of the Earth’satmosphere, and their change causedby increased human activities. Sub-millimeter (submm)-wave technologycan be said to be still in its infancycompared with spectroscopic tech-niques in other frequency regions,such as optical and infrared.

At present, a new generation of instru-ments toward the higher frequencymeasurements, submm-wave and THzregion is emerging in response to theincreased demands imposed by near-future sensing technology to fulfillincreased accuracy and precision. Ingeneral, detection sensitivity can behigher in submm-wave region due tothe stronger line intensity than that inthe millimeter region, making submm-wave observation more advantageousin identifying molecular species in theEarth’s atmosphere. State-of-the-artdetector systems will be implementedin these remote sensing instruments,giving superb sensitivity, and a num-ber of different species can be monito-red simultaneously; this is essential indetermining the chemical interactionschemes occurring in the atmosphereof our own planet.

The UARS/MLS (Upper AtmosphereResearch Satellite/Microwave LimbSounder) was the first satellite in milli-meter-wave region to monitor mole-cules in the Earth’s atmosphere. The Odin/SMR (Sub-MillimeterRadiometer) launched in February 2001is the first satellite in the submmregion. The AURA/MLS will be laun-ched in June 2004, which will probestandard molecules and will aim at aTHz line of OH. JEM/SMILES, plannedto be launched in 2008, will be equip-ped with an SIS (Super-conductorInsulator Super-conductor) receiversystem. It will be more sensitive (by afactor of 6-20) than standard Schottky-Barrier-Diode receivers, thanks to

updated super-sensitive detectiontechnology. This new instrument willopen up new horizons to observe spe-cies, which have been very difficult tomeasure otherwise due to their weakspectroscopic line intensities, lowconcentration, or rapidly changingaltitude dependence that makes a longaccumulation of their signal impracti-cal. Retrieval of meaningful informa-tion from the atmospheric measure-ments critically depends on theaccuracy of the laboratory spectrosco-pic measurements.

The aims of the workshop were: (i) todiscuss the accuracies of molecularparameters required and, in particular,the discrepancies often found amongthe data from various groups; (ii) theparameterisation of the atmosphericforeign continuum, which dominatesin atmospheric measurements, toderive the accurate abundance of thewater vapour from upper troposphereto lower stratosphere. This secondtopic includes the measurements ofthe foreign continuum from the milli-meter to far-infrared regions, its simu-lation based on the recent models, theobservations from space to deriveUpper Tropospheric Humidity (UTH),and the parameterisation of the foreigncontinuum on the basis of the theoryof the molecular collision complex inthe atmosphere.

We believe it is very important that theatmospheric community from NorthAmerica, Europe and Japan got toge-ther to discuss the accuracy require-ments imposed upon the experimentaldata and to sort out the sources of dis-crepancies often found among the dataobtained by various groups. InOctober 2001, a similar meeting washeld under the sponsorship ofNASA/JPL in San Diego, USA [1].This workshop was not exactly inten-ded to be a follow up of the San Diegomeeting, but we hoped it would comeup with some positive notes to solveoutstanding problems, such as moreconsistent and accurate determinationof the temperature dependence of the

pressure broadening coefficients.Background continuum in the submm-wave region that is not well characteri-sed was also one of the major topics.This is of common interest in bothatmospheric and astronomical obser-vations. It was very rewarding to havehad contributions in this workshopfrom both sides, as well as from detai-led theories.

The workshop was attended by 43researchers in the areas of atmosphericremote sensing, atmospheric opacityfor astronomy and molecular spectro-scopy.

Discussions

Microwave spectroscopy

A long list of tropospheric and strato-spheric molecules (H2O, HDO, O3, O3isotopes, HCl, CO, N2O, HNO3, HCN,H2CO, CH3CN, H2O2, ClO, HOCl, BrO,HOBr, HO2, SO2, OH, etc.) are monito-red by current and up-coming submmradiometers (e.g., MLS, ASUR,Odin/SMR, B-SMILES, JEM/SMILES).The accuracy of molecular parametersand discrepancies of the data fromvarious groups were discussed in thissession. F. DeLucia, B.J. Drouin,G. Wlodarczak, G. Cazzoli, andT. Amao presented the current statusand some of the outstanding problemsabout the systematic errors. They car-ried out precise rotational linewidthmeasurements, but statistically signifi-cant discrepancies persist among thosegroups. Inter-comparison of micro-wave spectral lineshape measurementsshould be made to resolve this issue.

From the discussions that followed theoral and poster presentations, it wasgenerally agreed that the accuracy ofthe spectroscopic parameter seemed tobe good for the broadening parametersbut the temperature dependences tur-ned out to be much more problematic,presumably due to the systematicerrors on the temperature measure-ments.

31

Accuracy required from submmremote sensing observations

This session was addressed to discussthe accuracy of the molecular parame-ters required from the current satellitesubmm-wave remote sensing mission.C. Verdes pointed out that the quantitymeasured by the satellites containsimplicit information on the atmosphe-ric state (e.g., molecular speciesvolume mixing ratio profiles, tempera-ture profile). An uncertainty in thespectroscopic parameters will lead to asystematic retrieval error. Therefore, athorough and careful investigation intothe current accuracy of the spectrosco-pic parameters and their impact on theretrieval are necessary. She gave therequirements for accuracy of the spec-troscopic parameter error from theretrieval results from a MASTER studyin the 300 GHz region. J. Urban show-ed the overview of Odin/SMR measu-rements and retrieval. He also discus-sed the required accuracy of pressurebroadening parameter of H2O, HDO,and H218O from the sensitivity studyof the Odin/SMR measurements.P. Hartogh gave a talk on the future ofsubmm wave limb emission sounders.The Heterodyne Instrument for the FarInfrared (HIFI) on the Herschel SpaceObservatory (HSO) and the GermanReceiver for Astronomy at THz fre-quencies (GREAT) on the Stratosphe-ric Observatory for Infrared Astronomy(SOFIA) are two new microwave ins-truments covering submm wave bandsbetween 500-1900 GHz (HIFI) and1600-5000 GHz (GREAT). In prepara-tion of the anticipated operation of theinstruments in 2005 (GREAT) and2007 (HIFI), they have performedmicrowave radiative transfer andretrieval calculations for a number ofmolecules with the main emphasis onwater vapour. The boundary condi-tions of the modelling were brieflydescribed and some results includingmodelled spectra and required observa-tion times were presented. J. Inatani,who is the PI for the SMILES instru-ment team, presented the CurrentStatus of JEM/SMILES. Y. Kasai dis-cussed the accuracy of O3 isotope measured by ASUR and SMILES, both using high sensitivity super-conductive SIS receivers.

From the discussions following theoral and poster presentations, thespectroscopic requirements that weredeemed to be important for atmosphe-ric sensing are: (1) Uncertainty of thepressure broadening parameter γ0(broadening coefficient at 296K)should be less than 3% for the mole-

cules, such as ozone; (2) The retrievalresult is not very sensitive with tempe-rature dependence, as when comparedwith γ0. (Figure 1, p. IV)

Atmospheric continuum

This session was addressed to theatmospheric continuum in submm andfar-infrared region. The final goal ofthis discussion was to derive accuratehumidity from upper troposphere tolower stratosphere, for example UTH,from global observations. There arethree different perspectives: (1) Therecent measurements of the atmosphe-ric background continuum from themillimeter to far-infrared regions; (2) The modelling of the atmosphericcontinuum by theory of the inter-molecular interaction; (3) How toderive UTH from the continuum mea-surements of the satellite microwavelimb emission, and how important it isin atmospheric sciences? (1) The atmospheric background conti-nuum is of common interest to atmo-spheric scientists and astronomers;this component is better known asatmospheric opacity for astronomers.They have studied opacity of the atmo-sphere in order to observe the emis-sion from molecules in the inter-stellarmolecular clouds; two astronomers,S. Matsushita and J.R. Pardo, gave atalk about Fourier TransformSpectrometer (FTS) measurements ofatmospheric opacity and comparisonswith the recent models; (2) The atmospheric continuum is alsoof interest to the molecular physicistsas an edge of the spectrum line shapedue to a molecular collision complexformation; R.H. Tipping and Q. Mapresented theoretical research toexplain the atmospheric continuumfrom the microwave to far-infraredregion; (3) The measurements of the atmo-spheric continuum by satellite micro-wave limb emission inform us aboutthe humidity of the upper troposphere;W.G. Read presented a talk on theMeasurement of UTH from theUARS/MLS and N. Eguchi discussedIntraseasonal variations of watervapour and cirrus clouds in the tropi-cal upper troposphere using the UTHderived by W.G. Read et al.

From the discussions following oralpresentation, it can be concluded thatthere is still large uncertainty betweenthe observation and the model parame-terisation about (even more than) 20 %in the submm and far-infrared region.We should continue to exchange infor-mation between the theory and obser-

vations to derived more accuratehumidity from upper troposphere tolower stratosphere with high altituderesolution (Figure 2, p. IV).

Acknowledgements

We wish to thank the participants fortheir enthusiasm during the work-shop. We gratefully acknowledgeProf. Watanabe, Dean of Faculty ofScience, Ibaraki University. Thefinancial support was almost entirelyprovided by the SMILES Mission teamof Communications Research Labo-ratory (CRL). We express our sinceregratitude to all who contributed theirbest efforts to make this workshop a great success, in particular,Dr. Manabe, SMILES Group leader inCRL.

Those who are interested in obtaininga copy of the workshop proceedings[2], please contact Yasuko Kasai (ykasai@nict.go.jp).

Workshop web page: http://www2.crl.go.jp/dk/c214/Amano-meeting/

Reference

[1] Workshop on Laboratory SpectroscopyNeeds for Atmospheric Sensing, San Diego,California, 23-26 October 2001 Chair:Michael Kurylo, NASA / NIST, Organizer:K. Jucks, SAO/Harvard, and B. Sen,NASA/JPL, http://atmoschem.jpl.nasa.gov/

[2] Proceedings of the “InternationalWorkshop on Critical Evaluation of mm-/submm-wave Spectroscopic Data for Atmospheric Observations”, CRLConference Publication, January 2004.

�

32

Future SPARC and SPARC-related Meetings2004

01-08 June: Quadrennial Ozone Symposium “Kos 2004”, Kos, Greece (http://lap.physics.auth.gr/ozone2004/). Chair: C. S. Zerefos

09-14 June: 3rd Workshop on Long-term trends in the atmosphere, Sozopol, Bulgaria (http://www.stil.acad.bg:80/STIL/ws2004/). Chair of LOC: K. Georgieva

16-18 June: 8th Biennial HITRAN Conference, Cambridge, Massachusetts - USA

6-8 July: 6th UTLS Ozone Science Meeting, Lancaster University, UK (http://utls.nerc.ac.uk/).18-25 July: 35th COSPAR Scientific Assembly, Paris, France. (http://www.cospar2004.org/gb_welcome.htm) Chair: M.-L. Chanin (chanin@aerov.jussieu.fr)• Interdisciplinary lectures (relevant of SPARC): 21st July: P. Crutzen “First ENVISAT Results”; 23 July: C. Fröhlich “Solar Radiation and Climate” • SPARC co-sponsored sessions:

A 1.1: Atmospheric Remote Sensing: Earth’s Surface, Troposphere, Stratosphere and Mesosphere. Chair: J. Burrows

C.2.3: Long-term Changes of Greenhouse Gases and Ozone and their Influence on the Middle Atmosphere. Chair: D. Chakrabarty

C.2.5: Structure and Dynamics of the Arctic and Antarctic of the Middle Atmosphere. Chair: M. Rapp

D 2.1/C2.2/E 3/I: Influence of the Sun’s Radiation and Particles on the Earth’s Atmosphere and Climate. Chair: J. Pap

01-06 August: 3rd SPARC General Assembly 2004, Victoria Conference Centre, Victoria (BC), Canada (http://sparc.seos.uvic.ca/). Chairs: A. Ravishankara and T. Sheperd- Chemistry-climate coupling - Extratropical UT/LS - Stratosphere-troposphere dynamical coupling - Tropical tropopause layer - Detection, attribution and prediction - Other

A particular emphasis for this General Assembly will be chemistry-climate coupling.

16-20 August: 2004 Western Pacific Geophysics Meeting (AGU WPGM), Honolulu, Hawaii, USA (http://www.agu.org/meetings/wp04/).

16-26 August: ESA summer school on “Earth System Monitoring & Modelling, ESRIN, Frascati, Italy (http://envisat.esa.int/envschool/).

04-09 September: 8th International Global Atmospheric Chemistry (IGAC) Conference, Christchurch, New Zealand (http://www.IGAConference2004.co.nz/).

12-25 September: 14th National Summer School on Geophysical and Environmental Fluid Dynamics, Cambridge, UK (http://www.gefd.damtp.cam.ac.uk).

19 September - 01 October: 1st French-German Summer School on “Aerosols, Heterogeneous Chemistry and Climate, La Vieille Perrotine”, l’île d’Oléron, France (http://www.mpch-mainz.mpg.de/summerschool/Summerschool_website/).

26-30 September: 4th Annual Meeting of the European Meteorological Society - Part and Partner: 5th Conference on Applied Climatology (ECAC), Nice, France (http://www.copernicus.org/ems/2004/index.htm).

Co-ChairsA. O'Neill (UK)A. Ravishankara (UK)

SSG Members Ex-Officio membersJ. Burrows (Germany) COSPAR : J. Gille (USA)P. Canziani (Argentina) IGAC : D. Parrish (USA), C. Granier (France) K. Law (France)K. Hamilton (USA) NDSC : M. Kurylo (USA)D. Hartmann (USA) SCOSTEP : M. Geller (USA)T. Peter (Switzerland) WMO/GAW : L. Barrie (Switzerland)U. Schmidt (Germany)T. Shepherd (Canada)S. Yoden (Japan)V. Yushkov (Russia)

SPARC Scientific Steering GroupDirector: M.-L. Chanin Project scientist: E. Oikonomou Manager: C. Michaut

Service d'Aéronomie, CNRS, BP 391371 Verrières-le-Buisson cedex, France Tel: +33- 1 64 47 43 15Fax: +33- 1 64 47 43 16Email: sparc.office@aerov. jussieu.frhttp://www.aero.jussieu.fr/~sparc/Published by Météo-France - Direction commerciale et de la communication

ISSN 1245-4680 - Dépôt légal 3e trimestre 2004

Composition of the SPARC Office

Edited by the SPARC Office

I

Comprehensive Summary on the Workshop on “Process-Oriented Validation of CoupledChemistry-Climate Models”

� Figure 4Polar chemical ozone loss. Variation of the overall chemicalozone loss in ten Arctic winters versus the winter-average of thevolume of air sufficiently cold for PSC existence (VPSC).Measurements are shown by coloured squares. Black points areresults from a chemical transport model. The slope of a fitthrough the points is a measure for the sensitivity of chemicalozone loss on changes in polar stratospheric temperatures andcan be used to validate the representation of chemical ozone lossin CCM calculations (Rex et al., 2003).

� Figure 1Wavenumber-frequency analy-sis. DJF transient wave varianceper day at 300 hPa in gpm/d forwavenumber 1 as computed bythe wavenumber-frequencyanalysis for westward (left) andeastward (right) travellingwaves. The upper panel showsthe 10-year mean of ECMWFERA-15 Re-analysis variances(1984-93, Gibson et al., 1997),the lower panel shows the 20-year mean of the CCM E39/Ctimeslice simulation “1990”(Hein et al., 2001).

� Figure 3Long-term global-mean temperature climatology.Vertical structure of the long-term, annual global-meantemperature (K) from observations (thick black line)and 13 models (thin coloured lines). Observations area 17-yr-mean (Pawson et al., 2000).

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� Figure 3History of five kilometer column densities of aero-sol surface area and volume in the northern midlatitudes, 1984-2004. The solid lines with intermit-tent error bars (±40 %) are from lognormal sizedistributions fit to ~ 200 aerosol profiles from bal-loon-borne in situ measurements above Laramie,Wyoming. Coloured symbols are SAGE II V6.1 esti-mates of surface area and volume from the SAGE IIweb site for all measurements between 38 and44°N with no restriction on longitude.

� Figure 1Schematic of the stratosphericaerosol lifecycle (from Hamill etal., 1997).

II

Report on the Assessment of StratosphericAerosol Properties: New Data Record,

but no Trend

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� Figure 2HALOE 5.26 µm aerosol extinctions as a function of latitude and altitude for the month of July in 1992, 1994 and 1997.White areas represent missing data and lines indicate average tropopause height. Measurements identified as cirrus wereremoved, resulting in the absence of data below the tropopause.

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IIISolar Variability and Climate: Selected Results from the SOLICE Project

� Figure 7Left: Vertical-meri-dional sections ofthe correlations bet-ween the 10.7 cmsolar flux and thede-trended zonalmean temperaturesin July; shaded foremphasis wherecorrelations areabove 0.5. Right:The respective tem-perature differences (K) between solarmaxima and mini-ma, shaded wherethe correlations areabove 0.5. Upperpanels: all years;middle panels: onlyyears in the eastphase of the QBO;lower panels: onlyyears in the westphase of the QBO.(NCEP/NCAR re-analyses, 1968-2002), (Labitzke,2003).

� Figure 5SAM II, SAGE and SAGE II stratospheric aerosol optical depth at1000 nm from 1979 through 2002. Profiles that do not extend tothe tropopause are excluded from the analysis leading to signifi-cant regions of missing data following the eruptions of El Chichónand Mt. Pinatubo in 1983 and 1991. Upper panel: original data.Lower panel: after gap-filling using auxiliary measurements (seetext).

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Report on the Assessment of Stratospheric Aerosol Properties:New Data Record,but no Trend •

� Figure 1Retrieval case study for Odin/SMR observa-tions of H2O-16 (left) and HDO (right) taken onSeptember 12, 2002 around the equator usingtwo bands centred at 488.9 and 490.4 GHz,respectively. Top: spectral measurements (thingreen lines) and fits (thick yellow lines) for tan-gent altitude of 20, 30, 40, and 50km. Bottom:retrieved profiles with error bars. Thick errorbars indicate the error due to intrinsic receivernoise, thin error bars represent the total retrie-val error including also the smoothing errordue to the limited altitude resolution of measu-rement. A priori profiles and errors are alsoplotted. Corresponding averaging kernel func-tions indicating altitude ranges and resolution(FWHM) are shown as well. (J. Urban andOdin/SMR team, Observatoire de Bordeaux)

� Figure 2Longitude-latitude sections of: (a) saturationmixing ratio from temperature [ppmv](contours and shading) and horizontal windcomponents [m/s] (vectors) at 100 hPa; and(b) water vapour mixing ratio [ppmv] (shading)and cirrus cloud frequency (contours) fromDay -15 to Day +5 every five days. In (a) a redstar indicates convective center on each day.Contour intervals are 1.0 [ppmv]. The shadingindicates less than 5.0 [ppmv]. The dark sha-ding indicates less than 3.0 [ppmv]. In (b)contour intervals are drawn with a step of20%.(Eguchi et al.).

IV

Report on the “International Workshop on CriticalEvaluation of millimeter-/sub-millimeter-wave

Spectroscopic Data for Atmospheric Observations”

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