Major discrepancies Major discrepancies in the analyzed wind in the analyzed wind

in the tropicsin the tropicsOreste RealeOreste Reale

GESTAR-USRAGESTAR-USRA

andand

NASA GSFC NASA GSFC

Earth Sciences Division Earth Sciences Division

MotivationMotivation

Operational analyses and state-of-the-art Operational analyses and state-of-the-art reanalyses show increasing agreement in reanalyses show increasing agreement in the extra-tropical atmosphere.the extra-tropical atmosphere.

However, large discrepancies still occur in However, large discrepancies still occur in major features of the tropical atmosphere.major features of the tropical atmosphere.

These discrepancies are present in both These discrepancies are present in both seasonal climatologies and instantaneous seasonal climatologies and instantaneous snapshots, and indicate the imperative snapshots, and indicate the imperative need of additional wind dataneed of additional wind data

OutlineOutline

African Easterly JetAfrican Easterly Jet ( (climatologyclimatology of of structure and structure and instability propertiesinstability properties) in state-of-the-art ) in state-of-the-art reanalysesreanalyses (ERA-40, NCEP-R, JRA-25 and MERRA)(ERA-40, NCEP-R, JRA-25 and MERRA)

AEJAEJ representation on representation on weather-time-scales weather-time-scales in in operational analysesoperational analyses during SOP-3 NAMMA during SOP-3 NAMMA (2006)(2006)

Somali JetSomali Jet inin MERRAMERRA and and NCEP operationalNCEP operational (2010)(2010) Mid-tropospheric flow over the entire tropical Mid-tropospheric flow over the entire tropical

Pacific in Pacific in August 2010August 2010 in in NCEP operational, ECMWF NCEP operational, ECMWF operational,operational, andand MERRA MERRA

Mis-representation or absence of observed Tropical Mis-representation or absence of observed Tropical cyclones in analyses (Indian Ocan, Atlantic, away cyclones in analyses (Indian Ocan, Atlantic, away from HH flights) in from HH flights) in operational analyses operational analyses

ConclusionsConclusions

AEJ and its instability properties in AEJ and its instability properties in state-of-the-art reanalysesstate-of-the-art reanalyses

New publication in New publication in 20122012 (Wu et al., 2012)(Wu et al., 2012) compares the compares the climatological representation of the climatological representation of the African Easterly Jet (AEJ)African Easterly Jet (AEJ) structurestructure and its and its instability propertiesinstability properties in in reanalysesreanalyses across a across a 22-year average22-year average

Despite revealing some instability property of the AEJ that Despite revealing some instability property of the AEJ that appears data-independent,appears data-independent, ERA-40, NCEP-R2, JRA-25 and ERA-40, NCEP-R2, JRA-25 and MERRAMERRA provideprovide different descriptionsdifferent descriptions of the AEJ of the AEJ horizontal horizontal structurestructure,, intensityintensity, and of , and of some properties that control wave some properties that control wave growth growth on a on a seasonal scale (JAS)seasonal scale (JAS)..

M.-L. C. Wu, Reale, O., S. Schubert, M.-L. C. Wu, Reale, O., S. Schubert, M. Suarez, C. Thorncroft, 2012: M. Suarez, C. Thorncroft, 2012:

African Easterly Jet: barotropic instability, waves and African Easterly Jet: barotropic instability, waves and cyclogenesis.cyclogenesis.

J. Climate, J. Climate, 25, 1489-1510.

Comparison of the AEJComparison of the AEJstructure in structure in MERRAMERRA, ,

ERA-40ERA-40, , NCEP-R2NCEP-R2, and , and JRA-25JRA-25. Speed, vorticity . Speed, vorticity and barotropic instability and barotropic instability

(Fig 2) (Fig 2)

Wu, M.-L, O. Reale, S. Wu, M.-L, O. Reale, S. Schubert, M. J. Suarez, Schubert, M. J. Suarez,

C. Thorncroft, 2012:C. Thorncroft, 2012:African Easterly Jet: African Easterly Jet: barotropic instability, barotropic instability,

waves and cyclogenesis.waves and cyclogenesis.Journal of Climate, 25, Journal of Climate, 25,

1489-1510.1489-1510.

From From Wu et al. (2010)Wu et al. (2010)

Fig 2Fig 2

The analyses differ in terms ofThe analyses differ in terms ofstrengthstrength of the low-level of the low-level

monsoonal flowmonsoonal flow, , slope of the slope of the barotropically unstablebarotropically unstable part of the part of theAEJ, AEJ, horizontal shear distributionhorizontal shear distribution. .

All Figures show a All Figures show a 22-year JAS average22-year JAS average

Large discrepancies between snapshots of Large discrepancies between snapshots of analyzed representation of the African analyzed representation of the African

Monsoon-Eastern Tropical Atlantic regionsMonsoon-Eastern Tropical Atlantic regions

TheThe African Easterly Jet African Easterly Jet at about 600hPa,at about 600hPa, thethe low-level low-level monsoonal flow monsoonal flow (predominantly southwesterly between (predominantly southwesterly between 1000 and 800 hPa)1000 and 800 hPa) and theand the Tropical Easterly Jet Tropical Easterly Jet (between 200 and 100 hPa)(between 200 and 100 hPa) are theare the critical players critical players inin Atlantic tropical development.Atlantic tropical development.

Comparison between operational Comparison between operational NCEP analysesNCEP analyses and and GEOS-5GEOS-5-produced analyses reveal -produced analyses reveal serious discrepanciesserious discrepancies

Validation against vertical sounding in the area at Cape Validation against vertical sounding in the area at Cape Verde (15N, 23.5W) produced during the 2006 NAMMA Verde (15N, 23.5W) produced during the 2006 NAMMA campaign,campaign, show that both analyses have large errors show that both analyses have large errors

Huge discrepancies between Huge discrepancies between GEOS-5 and NCEP operational analysesGEOS-5 and NCEP operational analyses

Wind at 5-15N, Wind at 5-15N, 500-600 hPa, has500-600 hPa, hasopposite opposite direction!direction!

Only in the tropicsOnly in the tropicsthe two analysesthe two analysesdiffer substantiallydiffer substantially

Section at 23.5WSection at 23.5W

Largest differences between reanalyses are in the tropics, Largest differences between reanalyses are in the tropics, at about 15N (at about 15N (on the order of 12m/son the order of 12m/s))

larger even thanlarger even thandiscrepancies in the southern hemisphere jet streamdiscrepancies in the southern hemisphere jet stream

NCEPNCEP

GEOS-5GEOS-5

Huge differences in the entire tropical zonal flow Huge differences in the entire tropical zonal flow from 20S to 20N at all levels from 20S to 20N at all levels

Largest Largest mid-troposphericmid-tropospheric wind difference is wind difference is in the tropics, at 0-10Nin the tropics, at 0-10N

GEOS-5GEOS-5 analyses analysesproduce a produce a weakerweaker easterly floweasterly flowthan than NCEPNCEP

GEOS-5GEOS-5

NCEPNCEP

Largest Largest low-tropospheric windlow-tropospheric wind difference is difference is in the tropics, between 10S and Equatorin the tropics, between 10S and Equator

Opposite-sign Opposite-sign discrepancydiscrepancywith respect to with respect to previous slide: previous slide: GEOS-5GEOS-5 analyses analysesproduce produce stronger stronger easterly flow than easterly flow than NCEPNCEP))

NCEPNCEP

GEOS-5GEOS-5

Additional vertical soundings at Cape Verde during Additional vertical soundings at Cape Verde during SOP-3 (2006) provide the chance to validate SOP-3 (2006) provide the chance to validate

operational analyses and hindcast experimentsoperational analyses and hindcast experiments

One of the rare cases in which One of the rare cases in which NCEPNCEP and and GEOS-5GEOS-5 differ less than 5 m/s) differ less than 5 m/s)

Both NCEP and GEOS-5 miss theBoth NCEP and GEOS-5 miss theAEJ maximum at 600hPa. AEJ maximum at 600hPa. ErrorErrorlarger than 10 m/s at AJE level!!!larger than 10 m/s at AJE level!!!

NCEPNCEP vsvs

GEOS-5GEOS-5

obsobs

obsobs

Catastrophic Catastrophic non-systematicnon-systematic differences differences

NCEPNCEP provides a good representation of provides a good representation oflow-level and upper-level flows but misses low-level and upper-level flows but misses the AEJ. the AEJ. GEOS-5 GEOS-5 has huge errors at all levels has huge errors at all levels except at 600hPa.except at 600hPa.

NCEP NCEP and and GEOS-5GEOS-5 both missboth missthe low-level flow, with the low-level flow, with NCEPNCEP having havinglarger errors.larger errors.

NCEPNCEP vsvs

GEOS-5GEOS-5

obsobs

obsobs

Catastrophic Catastrophic non-systematicnon-systematic differences differences

GEOS-5GEOS-5 has a stronger AEJ. has a stronger AEJ. NCEPNCEP has a stronger AEJ. has a stronger AEJ.

NCEPNCEP vsvs

GEOS-5GEOS-5

Large differences in the Large differences in the atmospheric circulation over the atmospheric circulation over the

tropical Indian Oceantropical Indian Ocean

The The Somali JetSomali Jet, a localized, , a localized, very shallow jet partly very shallow jet partly controlled by the Indian monsoonal low and by the controlled by the Indian monsoonal low and by the orography of Eastern Africaorography of Eastern Africa, appears to be , appears to be very sensitivevery sensitive to different data assimilation systems or data to different data assimilation systems or data assimilation strategiesassimilation strategies

Its Its representation is of great importancerepresentation is of great importance in prediction of in prediction of the the Monsoon breaksMonsoon breaks, , development of tropical cyclonesdevelopment of tropical cyclones, , intensity of low-level moist flowintensity of low-level moist flow controlling controlling precipitationprecipitation

The circulation over the entire northern Indian Ocean is The circulation over the entire northern Indian Ocean is strongly impacted by observationsstrongly impacted by observations

Somali Jet: comparison between MERRA and Somali Jet: comparison between MERRA and NCEP operational NCEP operational

5-day average 5-day average

Somali Jet core position in MERRA and NCEP:Somali Jet core position in MERRA and NCEP:500 km of displacement,500 km of displacement,

very large very large heightheight and and shapeshape differences differences

SomaliSomaliJetJet

SomaliSomaliJetJet

Large, Large, non-systematicnon-systematic differences in the definition differences in the definition of the Somali Jet of the Somali Jet

and in the wind over the Indian Oceanand in the wind over the Indian Ocean

NCEP OperationalNCEP Operational vs vs MERRAMERRA

Five-day averageFive-day average, meridional section at 60E, meridional section at 60Efrom 65S to 65N, from 65S to 65N, at 900hPaat 900hPa and and 800 hPa800 hPa respectively respectively

SomaliSomaliJetJet SomaliSomali

JetJet

Pakistan Floods (2010)Pakistan Floods (2010) Catastrophic floods in late July and August 2010Catastrophic floods in late July and August 2010 3 sets of 45-day data assimilation runs3 sets of 45-day data assimilation runs: : July 15 to July 15 to

August 31August 31 with different with different AIRS data setsAIRS data sets 3 sets of 7-day forecasts3 sets of 7-day forecasts at 00z of every day for at 00z of every day for

every set of analysesevery set of analyses Assessment of Assessment of Global SkillGlobal Skill and evaluation of and evaluation of

Precipitation analysis and forecastPrecipitation analysis and forecast over region show over region show that the that the moist southerly flow against Pakistan is moist southerly flow against Pakistan is strongly affected by the assimilation strategystrongly affected by the assimilation strategy

Impact assessment on dynamics of the mechanismImpact assessment on dynamics of the mechanism Reale, O., W.K. Lau, J. Susskind, R. Rosenberg, Reale, O., W.K. Lau, J. Susskind, R. Rosenberg,

(2012), AIRS Impact on Analysis and Forecast of an (2012), AIRS Impact on Analysis and Forecast of an Extreme Rainfall event (Indus River Valley, Pakistan, Extreme Rainfall event (Indus River Valley, Pakistan, 2010) with a global data assimilation and forecast 2010) with a global data assimilation and forecast system.’’system.’’ J. Geophys. Res.,J. Geophys. Res., 117, D08103, 117, D08103, doi:10.1029/2011JD017093. doi:10.1029/2011JD017093.

7-day moisture transport across the entire forecast7-day moisture transport across the entire forecastinitialized at 00z22July initialized at 00z22July

Reale et al. (2012)Reale et al. (2012)

Contour:Contour:Vertically integratedVertically integrated7-day mean total7-day mean totalMoisture fluxMoisture fluxShaded:Shaded:7-day7-day RETRET minus minusRAD RAD meridionalmeridionalMoisture fluxMoisture flux

Net increase ofNet increase ofNorthward merid.Northward merid.Transport towardsTransport towardsNorthern PakistanNorthern PakistanConsequent toConsequent toAIRS v5 retrievalAIRS v5 retrievalassimilationassimilation

Large differences between operational ECMWF, Large differences between operational ECMWF, NCEP and MERRA over the entire tropical Pacific NCEP and MERRA over the entire tropical Pacific

during strong La Nina conditions (Aug 2010)during strong La Nina conditions (Aug 2010)

Weather prediction over the tropical Pacific Weather prediction over the tropical Pacific is controlled by a good representation of is controlled by a good representation of the predominantly easterly flow and the predominantly easterly flow and periodic westerly bursts along the Equatorperiodic westerly bursts along the Equator

Large errors in the equatorial flowLarge errors in the equatorial flow propagate propagate away from the Equatoraway from the Equator affecting affecting TC genesisTC genesis prediction, and prediction, and TC track TC track forecastforecast as far as 30N/S as far as 30N/S

HugeHuge 600hPa zonal wind difference affects the 600hPa zonal wind difference affects the entireentire tropical Pacific in tropical Pacific in 20102010involving all 3 data setsinvolving all 3 data sets

Speeds are very comparable away from the tropicsSpeeds are very comparable away from the tropics

The largest 600hPa wind difference at 165W occurs The largest 600hPa wind difference at 165W occurs in the tropics, between in the tropics, between 20S and 10N20S and 10N

MERRAMERRA

ECMWFECMWF

NCEPNCEP

In addition to differences in the general circulation in In addition to differences in the general circulation in the Tropics, state-of-the-art operational systems can the Tropics, state-of-the-art operational systems can

completely miss completely miss existingexisting Tropical Cyclones. Tropical Cyclones.

Analyses are particularly deficient in the depiction Analyses are particularly deficient in the depiction of of developing, deepeningdeveloping, deepening and and transitioning transitioning tropical tropical cyclonescyclones

Analyses are deficient in representing cyclogenesis Analyses are deficient in representing cyclogenesis and existing deepening cyclones in the and existing deepening cyclones in the eastern eastern AtlanticAtlantic

Analyses are Analyses are particularly deficientparticularly deficient in representing in representing even even fully-developed fully-developed TCs over the Indian Ocean TCs over the Indian Ocean

TS Debby (2006) at 06z 24 Aug 2006TS Debby (2006) at 06z 24 Aug 2006Obs center slp 999 hPa; Max wind 22 m/sObs center slp 999 hPa; Max wind 22 m/s

NCEP analysesNCEP analysesdo do notnot produce produce

a a closed closed circulationcirculation

GEOS-5 An.GEOS-5 An.200km200km

displacement displacement error for centererror for center(obs. center X) (obs. center X)

Wind speed m/sWind speed m/s

Complete Complete miss of TC Nargismiss of TC Nargis (2008) in both (2008) in both operational operational NCEPNCEP and and MERRAMERRA analyses at a time when is declared analyses at a time when is declared

having having hurricane-level windshurricane-level winds by the JTPC and IMC by the JTPC and IMC

800x600km800x600kmContours Contours every 1hPaevery 1hPa

WINDS DOWINDS DONOT FORMNOT FORMA CLOSEDA CLOSEDCIRCULATIONCIRCULATION

800x600km800x600kmContours Contours every 1hPaevery 1hPa

X observed X observed cyclone’s center cyclone’s center

COMPLETELYCOMPLETELYFLAT PRESSUREFLAT PRESSURE

FIELDFIELD

WINDS DO NOT REACH 12m/sWINDS DO NOT REACH 12m/sWINDS DO NOT FORM A CLOSED CIRCULATIONWINDS DO NOT FORM A CLOSED CIRCULATION

Published study on the impact of AIRS, Published study on the impact of AIRS, focused on tropical cyclone Nargis (2008)focused on tropical cyclone Nargis (2008)emphasizes the difficulty of analysing TCs emphasizes the difficulty of analysing TCs

over the Indian Oceanover the Indian Ocean

Work published in 2009 shows some improvements in analysis Work published in 2009 shows some improvements in analysis over the over the tropicstropics in in the GEOS-5 DAS and forecasting model in in the GEOS-5 DAS and forecasting model consequent to assimilation of AIRS-derived information in consequent to assimilation of AIRS-derived information in CLOUDY CLOUDY areas. Case chosen: areas. Case chosen: catastrophic cyclone Nargis catastrophic cyclone Nargis which hit Burma causing devastating loss of lifewhich hit Burma causing devastating loss of life

Tropical Cyclones in the Northern Indian Oceans are extremely Tropical Cyclones in the Northern Indian Oceans are extremely difficult to analyze: operational global analyses often do not difficult to analyze: operational global analyses often do not represent these cyclones’ represent these cyclones’ position position (or (or even the TCs’ very even the TCs’ very existenceexistence) accurately. ) accurately. Forecasts are penalized by these poor Forecasts are penalized by these poor analysesanalyses

Reale, O., W. K. Lau, J. Susskind, R. Rosenberg, E. Brin, E. Liu, L.P. Riishojgaard, M. Fuentes, Reale, O., W. K. Lau, J. Susskind, R. Rosenberg, E. Brin, E. Liu, L.P. Riishojgaard, M. Fuentes, R. Rosenberg, 2009: AIRS impact on the analysis and forecast track of tropical cyclone Nargis in R. Rosenberg, 2009: AIRS impact on the analysis and forecast track of tropical cyclone Nargis in A global data assimilation and forecasting system. A global data assimilation and forecasting system. Geophys. Res. Lett., 36, L06812, doi: 10.1029/2008GL037122Geophys. Res. Lett., 36, L06812, doi: 10.1029/2008GL037122

Some improvement with AIRS v5 retrievalsSome improvement with AIRS v5 retrievals

Analysis obtained Analysis obtained assimilating AIRS assimilating AIRS cloudycloudy retrievals retrievals (version 5)(version 5)Well-definedWell-definedCycloneCycloneGreen:Green:Observed Observed TrackTrack

108-hour108-hourforecast (slp)forecast (slp)initialized from initialized from improved improved analysesanalyses

Green:Green:Observed Observed TrackTrack

CNTRL Analysis (above)CNTRL Analysis (above)And forecast (below): And forecast (below): No CycloneNo Cyclone

Accurate landfall is produced in the forecasts initialized Accurate landfall is produced in the forecasts initialized with AIRS: (Reale et al., 2009, with AIRS: (Reale et al., 2009, Geophys. Res. LettGeophys. Res. Lett.).)

ConclusionsConclusions State of the art reanalyses State of the art reanalyses (ERA-40, JRA-25, NCEP-R2 and (ERA-40, JRA-25, NCEP-R2 and

MERRA)MERRA) show susbtantial differences in the show susbtantial differences in the seasonally-averaged seasonally-averaged representation of the representation of the African Easterly JetAfrican Easterly Jet and more generally of and more generally of the circulation in the African Monsoon and tropical Atlantic the circulation in the African Monsoon and tropical Atlantic regionsregions

Operational analyses or reanalyses differ also at Operational analyses or reanalyses differ also at instantaneous instantaneous timestimes in the tropical region. On the contrary, in the tropical region. On the contrary, away from the away from the tropics, different analyses provide tropics, different analyses provide almost identicalalmost identical representations of the wind fieldrepresentations of the wind field

However, it appears evident that However, it appears evident that the global tropical wind fieldthe global tropical wind field is is a very deficient aspect of current tropospheric analysisa very deficient aspect of current tropospheric analysis

Despite changes in models and assimilation systems, and Despite changes in models and assimilation systems, and increase in resolution, increase in resolution, the representation of wind in the tropicsthe representation of wind in the tropics does not show much improvementdoes not show much improvement from from 2006 to 20102006 to 2010

Major discrepancies appear on Major discrepancies appear on all 3 basins:all 3 basins: Atlantic, Indian and Atlantic, Indian and Pacific OceansPacific Oceans on scales spanning from on scales spanning from storm-scalestorm-scale to to planetaryplanetary, , from from weatherweather to to seasonalseasonal

To reduce the errors in the analyzed wind field on To reduce the errors in the analyzed wind field on different scales in the tropics is of paramount importance different scales in the tropics is of paramount importance and should be the goal for the next-generation observing and should be the goal for the next-generation observing systemssystems