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Atmospheric Hydrological Cycle in the Tropics in Twentieth Century Coupled Climate Simulations. Hailan Wang and William Lau Laboratory for Atmospheres, NASA/GSFC. Climate Model Evaluation Project (CMEP). 30 th Climate Diagnostics and Prediction Workshop October 26, 2005. Motivation. - PowerPoint PPT Presentation
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Atmospheric Hydrological Cycle in the Tropics in Twentieth Century Coupled Climate Simulations
Hailan Wang and William Lau
Laboratory for Atmospheres, NASA/GSFC
30th Climate Diagnostics and Prediction WorkshopOctober 26, 2005
Climate Model Evaluation Project (CMEP)
Motivation
• Identify and understand long-term change of tropical hydrological cycle in 20th 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
Coupled GCMs (Cont’d)
– 16 CGCMs analyzed
– 1 run of each CGCM used• Monthly mean fields
• 1900-1999
– Linear trend (actual linear change over time period concerned)
• Models: 1950-1999
• Observations– 1979-1999 for GPCP precip
– 1984-1999 for ISCCP clouds
Model No.
Model Acronym Modeling group Country Atmosphere Resolution Ocean Resolution at Equator
1 CGCM3.1(T47) CCCMA Canada T47L31 1.851.85L29
2 CNRM-CM3 CNRM France T63L45 20.5L31
3 CSIRO-Mk3.0 CSIRO Australia T63L18 1.8750.84L31
4 GFDL-CM2.0 GFDL USA 2.52L24 11/3L50
5 GFDL-CM2.1 GFDL USA 2.52L24 11/3L50
6 GISS-EH NASA/GISS USA 54L20 22L16
7 GISS-ER NASA/GISS USA 54L20 54L13
8 FGOALS-g1.0 LASG/IAP China T42L26 11L33
9 INM-CM3.0 INM Russia 54L21 2.52L33
10 IPSL-CM4 IPSL France 3.752.5L19 21L31
11 MIROC3.2(hires) CCSR/NIES/FRCGC Japan T106L56 0.280.1875L47
12 MIROC3.2(medres) CCSR/NIES/FRCGC Japan T42L20 1.40.5L43
13 ECHAM5 MPI Germany T63L31 1.51.5L40
14 CCSM3 NCAR USA T85L26 1.1250.27L40
15 UKMO-HadCM3 UKMO UK 3.752.5L19 1.251.25L20
16 UKMO-HadGEM1 UKMO UK 1.8751.25L38 11/3L40
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 TempAnnual Mean 1950-1999
Rain Rate
Light: <1mm/day
Medium: 2-8mm/day
Heavy: >9mm/day
Distribution of GPCP Rain as a function of Rain RateAnnual Mean 1979-1999; Tropical Ocean
Clim
Trend
Upward motion enhances
OLR reduces
Chen et al (2002); Wielicki et al (2002)
Linear Change over 1950-1999
500mb
OLR at TOA
Cool ClimateTropical Ocean
TropopauseOLR
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 reducedmoderate rain
Increased light rain
Intensified deep convection
Strengthened updraft
Ocean surface
Warmer Tropical OceanWarm ClimateOcean surface
Enhanced Surface Evaporation
Conclusions• CGCMs are reasonably consistent in depicting aspects of long term
changes in the 20th 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