Atmospheric Hydrological Cycle in the Tropics in Twentieth Century Coupled Climate Simulations Hailan Wang and William Lau Laboratory for Atmospheres, NASA/GSFC 30 th Climate Diagnostics and Prediction Workshop October 26, 2005 Climate Model Evaluation Project (CMEP)

Motivation Identify and understand long-term change of tropical hydrological cycle in 20 th Century climate simulations by Coupled GCMs Precipitation Clouds Provide input for IPCC AR4 in 2007

Coupled GCMs State-of-the-art Fully coupled –Time signature differs Driven by time-varying external climate forcings –No agreed-upon forcing functions –The diversity in external forcing in the CGCMs is regarded as a measure of forcing uncertainties

/research/modeling/ NASA GISS_E

Coupled GCMs (Cont’d) –16 CGCMs analyzed –1 run of each CGCM used Monthly mean fields –Linear trend (actual linear change over time period concerned) Models : Observations – for GPCP precip – for ISCCP clouds

Model No. Model AcronymModeling groupCountryAtmosphere ResolutionOcean Resolution at Equator 1CGCM3.1(T47) CCCMACanadaT47L  1.85  L29 2CNRM-CM3 CNRMFranceT63L45 2  0.5  L31 3CSIRO-Mk3.0 CSIROAustraliaT63L  0.84  L31 4GFDL-CM2.0 GFDLUSA 2.5  2  L24 1  1/3  L50 5GFDL-CM2.1 GFDLUSA 2.5  2  L24 1  1/3  L50 6GISS-EH NASA/GISSUSA 5  4  L20 2  2  L16 7GISS-ER NASA/GISSUSA 5  4  L205  4  L13 8FGOALS-g1.0 LASG/IAPChinaT42L26 1  1  L33 9INM-CM3.0 INMRussia 5  4  L212.5  2  L33 10IPSL-CM4 IPSLFrance 3.75  2.5  L19 2  1  L31 11MIROC3.2(hires) CCSR/NIES/FRCGCJapanT106L   L47 12MIROC3.2(medres) CCSR/NIES/FRCGCJapanT42L  0.5  L43 13ECHAM5 MPIGermanyT63L  1.5  L40 14CCSM3NCARUSAT85L  0.27  L40 15UKMO-HadCM3UKMOUK3.75  2.5  L  1.25  L20 16UKMO-HadGEM1UKMOUK1.875  1.25  L381  1/3  L40 USA: 5; France: 2; Japan: 2; UK: 2; Australia: 1; Canada: 1; China:1; Germany: 1; Russia: 1

HadCRU (#17); NCEP CAMS (#18); NOAA extended SST (#19) Linear Change of Surface Temp Annual Mean

GPCP (#17) Linear Change of Precip Annual Mean

Linear Trend of Surface Temp ( ) and Precip ( ) 16 AR4 Model EnsMean Obs

Rain Rate Light: <1mm/day Medium: 2-8mm/day Heavy: >9mm/day Distribution of GPCP Rain as a function of Rain Rate Annual Mean ; Tropical Ocean Clim Trend

GFDL CM2.0 NASA GISS ER MIROC3.2 hires NCAR CCSM3 UKMO HadCM3 GPCP Trend_Model*4

ISCCP (#17) Linear Change of Total Cloud Cover Models ( ) vs ISCCP/4 ( )

[1000mb-10mb] [30S-30N] [0-360E; 30S-30N] Clim and Linear Trend of 3-D Cloud in GFDL CM2.0

Clim Linear Trend

Upward motion enhances OLR reduces Chen et al (2002); Wielicki et al (2002) Linear Change over  500mb OLR at TOA

Cool Climate Tropical Ocean Tropopause OLR Surface Evaporation Tropopause OLR More cold and bright high cloud at tropopause and lower stratosphere Less mid-to-low cloud Less high cloud Less OLR Enhanced heavy rain Greatly reduced moderate rain Increased light rain Intensified deep convection Strengthened updraft Ocean surface Warmer Tropical Ocean Warm Climate Ocean surface Enhanced Surface Evaporation

Conclusions CGCMs are reasonably consistent in depicting aspects of long term changes in the 20 th Century climate and the tropical hydrological cycle: –Surface warming over tropical ocean and land –Increasing/decreasing precipitation over tropical ocean/land –Increasing heavy and light rain, but decreasing moderate rain –A reduction in total cloud cover in the tropics. CGCMs significantly underestimate the magnitudes of the observations, by a factor of at least 4. –This likely leads to gross errors in model simulation of tropical radiative fluxes Difference between CGCMs and observations –Time scale –CGCMs: certain processes may be missing –Obs: e.g. problems in retrieving high level thin clouds

Future Improvement in representing physical processes associated with clouds and their interaction with radiation in the CGCMs Observational data –Quality –Long term