relevant & demanding test for gcms
DESCRIPTION
THE DIURNAL CYCLE OF CONVECTION MODELLING ISSUES Françoise Guichard (CNRM, Toulouse in France). « Even today, many comprehensive GCMs use a daily mean insolation in place of the true diurnally varying insolation » from Randall et al. (1985). relevant & demanding test for GCMs - PowerPoint PPT PresentationTRANSCRIPT
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relevant & demanding test for GCMs
assess physical parameterizations : radiation, surface exchanges, boundary layer, convective & cloud processes
« Even today, many comprehensive GCMs use a daily mean insolation in place of the true diurnally varying insolation »from Randall et al. (1985)
THE DIURNAL CYCLE OF CONVECTION MODELLING ISSUES
Françoise Guichard (CNRM, Toulouse in France)
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initiation
dévelopment dissipation
stationarity
life de vie, transitions, régimes
parametrization: not only a set of independent schemes importance of their mutual interactions!
convectionscheme
convectiveboundary layer
cloudproperties
density current
diurnal cycle of convection
radiation
large-scale motions
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difficult to reproduce by GCMs (illustrated next slides)
e.g. monthly mean & diurnal cycle both correct at the same time quite challenging Lin et al. (2000)
re-tuning: may be quite delicate (e.g. shift convective to stratiform dominant, radical modification of the cloud cover!)
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CLIMATE GCM
unified climate model
quite resasonable agreement (caution: not at all the case for all GCMs!) frequently too weak, e.g. Royer et al. (2000), Lin et al. (2000),
Dai et al. (1999)
precipitation: amplitude of the diurnal harmonic Yang & Slingo (2001)
OBERVATIONS
CLAUS dataset
0.5 1 2 4 6 10 14 18 22
(mm/day)
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Yang & Slingo (2001)precipitation: phase of the diurnal harmonic
OBERVATIONS
CLAUS dataset
local solar time (hour)
0 2 4 6 8 10 12 14 16 18 20 22 24
CLIMATE GCM
unified climate model
precipitation too early by several hours compared to observations
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comparaison of the phases of the diurnal harmonic of rainfall in obs & 3 GCMs
0 2 4 6 8 10 12 14 16 18 20 22 24
Unified Model
(Met Office)
ARPEGE NWP
(J.-M. Piriou)
ECMWF IFS
(provided by A. Beljaars)
observations
satelite data
CLAUS
Yang &
Slingo (2000)
hour (local solar time)
(J. M. Piriou)
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approch to the problem
from there, how to proceed?
analysis of the interactions between parametrizations in 3D can rapidly become a nightmare... (complex feedback loops, compensation errors...)
it is misleading to concentrate on one given field, like precip.
approach developed within GCSS & EUROCS
not the final solution within 3 years for each GCM involved but useful insights (which aspect to work on?...)
use this intercomparison frame to point to various problems which are not model dependent
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GCM picture from Colostate web page
bring together a community of modelers : hierarchy of scales
LES & CRMs --- SCMs --- RCMs & GCMsobs obs
LES: Large Eddy SimulationCRM: Cloud Resolving ModelSCM: Single Column ModelRCM: Regional Climate ModelGCM: General Circulation Model
GCSS : Gewex cloud system studyEUROCS : EUROpean Cloud Systems
z=
70m
to 6
00m
x= y= 1km
clouds
focus on well known GCM problems
within EUROCS, diurnal cycle of: shallow non precipitating convection over landdeep convection over landmarine stratocumulus
CRM-simulated convective system: illustration, from Guichard et al. (1997)
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scheme from
EUROCS project
description
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SIMULATION OF AN OBSERVED CASE FOR VALIDATION PURPOSE
an example : comparison with obs, min-max envelope for CRMs & SCMs
better agreement & less scatter among CRM results that SCM ones
min max
(figures : from EUROCS report)
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comparison CRMs & SCMs (no observations available)
scatter linked to the microphysics for CRMs in the upper troposphere
very weak convective downdraughts in several SCMs
obviously room for CRMs improvements
however much more consistency among CRMs than SCMs
(figures : from EUROCS report)
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diurnal cycle of shallow cumulus
cloud fraction
results at the end of the project
Lenderink et al.(2004)intercomparaison SCMs
Brown et al.(2002)intercomparaison LES
crucial role of the coupling between BL & cumulus parametrization !
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Large spread in the amount of predicted rainfall but…the typical weakness found in GCMs is reproduceddeep convection starts later in CRMs
Why?
Guichard et al. (2004)
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diurnal cycle of
convectionin CRMs
Guichard et al. (2004)
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and q in the BL: CRMs
at noon
in the late afternoon
differences in BL at
noon consistent
with further differences
in moist convection developme
nt
Guichard et al. (2004)
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and q in the BL: SCMs
at noon
in the late afternoon
Guichard et al. (2004)
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characteristics of parameterized downdrafts
SCM1SCM2
Mup
2.Mdown
Mup
2.Mdown
contrasted behaviours among SCMsvarious relative intensities (not directly linked to their impact though)
significant impact on BL development in the morning, additional source of pb
Guichard et al. (2004)
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In CRMs, convective draughts are predominantly upwards at first, convective downdraughts develop later
Clearly need a dedicated effort/careful analysisHypothesis in SCMs? How are they supported or not by CRMs?…
(figure from EUROCS web page)
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e and saturation deficit in the whole column at midnight
CRMs
SCMs
initialprofile
Guichard et al. (2004)
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Q1/Q2: time mean profiles
Guichard et al. (2004)
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Q1/Q2: time height evolution
some time lag between Q2 & Q1not in SCMs
(figures from EUROCS web page)
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CLOUDS
(figures from EUROCS web page)
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(figures from EUROCS web page)
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clouds
Guichard et al. (2004)
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CIN (J. kg-1)
Chaboureau et al. (2004)
1: quasi-dry convectionCIN , sat def ~ cst
2: shallow convectionCIN ~ cst sat def (moistening)
3: deep convection
CIN , sat def
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CRMs
SCMs
Guichard et al. (2004)
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Diurnal cycle of convective stability
Guichard et al. (2004)
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Guichard et al. (2004)
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Guichard et al. (2004)
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summary (1/2)
a simple framework (case-study) for CRMs and SCMs allows to identify weaknesses of conv. param. / type of situation
CRMs: provided useful informations despite weaknesses (BL & shallow cumulus) about the succession of convective regimes
most SCMs cannot handle properly such a succession of regimes
difficulties with boundary layer simulation
too early triggering of convection can be related to their too strong link with CAPE independently of BL activity their lack of sensitivity to moisture / CRMs
additionnal problemes arise from the param. of downdraughts…
strong & various impacts on the simulated clouds (each SCM a special case)
on going work, on entrainment (methods) ...
in //: analysis of data / transition phases required
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SUMMARY (2/2)
initiation
dévelopment dissipation
stationarity
life cycle, transitions, régimes
parametrization: not only a set of independent schemes
their mutual interactionsconvectionscheme
convectiveboundary layer
cloudproperties
density current radiation
not much progress can be expected without an improvement of both schemes & interactions
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REFERENCES, in chronological order with respect to slides
• Randall, D. A., Abeles, J. A., and Corsetti, T. G., 1985: Seasonal simulations of the planetary boundary layer and boundary-layer stratocumulus clouds with a general circulation model, J. Atmos. Sci., 42, 641-676.
• Lin, X., Randall, D. A. and Fowler, L. D., 2000 : Diurnal variability of the hydrologic cycle and radiative fluxes: Comparisons between observations and a GCM. J. Climate, 13, 4159–4179.
• Yang, G. Y. and Slingo, J. M., 2001 : The diurnal cycle in the tropics. Mon. Wea. Rev., 129, 784-801.
• EUROCS web page: http://www.cnrm.meteo.fr/gcss/EUROCS/EUROCS.html
• Guichard, F., Lafore, J.-P., and Redelsperger, J.-L., 1997, Thermodynamical impact and internal structure of a tropical convective cloud system, Quart. J. Roy. Meteor. Soc., 123, 2297-2324
• Royer, J.-F., Belamari, M., Céron, J.-P., Chaumat, L., Guérémy, J.-F., Piriou, C., Redelsperger, J.-L., Royer and Tyteca, S, 2000 : Cloud Archive User Service (CLAUS), CNRM-ENM final report (ENV4-CT96-0356).
• Dai, A., Giorgi, F. and Trenberth, K. E., 1999 : Observed and model simulated precipitation diurnal cycle over the contiguous United States. J. Geophys. Res., 104, 6377-6402.
• Lenderink, G., Siebesma, A. P., Cheinet, S., Irons, S., Jones, C. J., Marquet, P., Müller, F., Olmeda, D., Sanchez, E. and Soares, P., 2004 : The diurnal cycle of shallow Cumulus clouds over land: A single column model intercomparison study. submitted to Quart. J. Roy. Met. Soc., in press.
• Brown, A. R., Cederwall, R. T., Chlond, A., Duynkerke, P. G., Golaz, J.-C., Khairoutdinov, M., Lewellen, D. C., Lock, A. P., Macvean, M. K., Moeng, C.-H., Neggers, R. A. J., Siebesma, A. P. and Stevens, B., 2002: Large-eddy simulation of the diurnal cycle of shallow cumulus convection over land. Quart. J. Roy. Met. Soc., 128, 1075–1094.
• Chaboureau, J.-P., Guichard, F., Redelsperger, J.-L. and Lafore, J.-P., 2004 : Role of stability and moisture on the development of convection, submitted to Quart. J. Roy. Met. Soc., in press.
• Guichard, F., Petch, J. C., Redelsperger, J.-L., Bechtold, P., Chaboureau, J.-P., Cheinet, S., Grabowski, W. W., Grenier, H., Jones, C. J., Koehler, M., Piriou, J.-M., Tailleux R., and Tomasini, M., 2004: Modelling the diurnal cycle of deep precipitating convection over land with cloud-resolving models and single column models, Quart. J. Roy. Meteor., in press.