Performance of GEM in the GCSS Pacific Cross-section Intercomparison Project

(GPCI)

Yanjun Jiao Paul Vaillancourt

Colin Jones

GEM-DAY@ OuranosJune 12, 2007

GPCI DATA RESULTS SUMMARY

GCSS (GEWEX Cloud System Study) is developing better parameterizations of cloud systems for climate models by improving our understanding of the physical processes in different types of cloud. There are 6 working groups:• Boundary Layer Clouds

• Cirrus Cloud Systems

• Extra Tropical Layer Clouds

• Precipitating Convective Cloud Systems

• Polar Clouds

• GPCI - GCSS Pacific Cross-section Intercomparison

Cases Studies using SCM/CRM/LES

Overall performance in 3D climate models (GCM/RCM)

GPCI is a working group of GCSS

GPCI is a working group of GCSSGPCI focuses on the physics, including

clouds, turbulence, convection and radiation, in the 3D climate models.

Model results are analyzed along a cross-section in the Pacific, from the stratocumulus regions off the coast of California, across the shallow cumulus areas, to the deep convection regions of the ITCZ.

Free to choose model resolution and domain

Run in climate mode with SST prescribed (June-July_August started from May 20, 1998 and 2003)

Simple but efficient (1 section, 3 clouds)

Datasets

GPCP 1DD GPCP high resolution daily data (0.5° PCP)

TRMM Tropical Rainfall Measurement Mission (0.25° PCP)

SSM/I Special Sensor Microwave/Imager (CLW and PW)

ISCCP International Satellite Cloud Climatology Project (CLDT)

CERES Clouds and the Earth’s Radiant Energy System (OLR)

WHOI Woods Hole Oceanographic Institution (QLA and HFS)

ERA40 ECMWF reanalysis (1998)

(CLDT CLWT PCVW PCPS PCPC HFS QLA FSS FDL FSG FSS FST OLR FLTC FLGC FSTC FSGC)

NRA2 NCEP/NCAR reanalysis II

(CLDT PCPT HFS QLA FSS FDL)

SSM/I

GEM

Precipitable water in the atmosphere (kg/m2)

SSM/I

GEM

30-50g/m2 50-75g/m2

Cloud liquid water (g/m2)

ERA-40 SSM/I BMRC CSU MMF GISS GKSS GEM CRCMM

-1 2 5 8 11 14 17 20 23 26 29 32 350

50

100

150

200

250

300

350

400

450

500

JJA 1998

Is GEM a bad model?

Relative humidity (%)

ISCCP

10% more 40% less

GEM

ERA40

-1 2 5 8 11 14 17 20 23 26 29 32 350

20

40

60

80

100

ERA-40

ISCCP

BMRC

CSU MMF

GISS

GKSS

NCEP G&M3

GEM

CRCMM

latitude (degrees)

JJA 1998

Cloud cover (%)

Precipitation (mm/day)

GEM

TRMM

GPCP

convective

stratiform

Zonal wind (m/s)

Meridional wind (m/s)

Vertical velocity (-Omega in Pa/s)

GEM

WHOI

NRA2

ERA40

Sensible heat flux (W/m2)

Latent heat flux (W/m2)

Shortwave radiation (W/m2)

GEM

ERA40

ERA40

GEM

GEM

CERES

Longwave radiation (W/m2)

GEMLAM_PSC - precipitating shallow convection

GEMLAM_REG -precipitating shallow convection scheme, moist TKE PBL, the turbulent mixing length of Blackadar rather than Bougeault-Lacarrere, surface roughness over water according to Charnock.

GEMLAM_PSC

GEMLAM_REG

GEM

SSM/I

GEMLAM_PSC

GEMLAM_REG

GEM

ISCCP

GEMLAM_PSC

GEMLAM_REG

GEM

TRMM

ERA40

Siebesma et al. (2004)

•GEM well simulates the precipitable water in the atmosphere but significantly underestimates the CLW in the stratocumulus region (>=50g/m2 less than SSM/I) and overestimates CLW in the shallow regions (20~50g/m2) (a precise partitioning/prognostic method is needed).

•GEM very well simulates the seasonal mean precipitation along the cross-section except in the transition area between deep and shallow convection (too strong/too many deep convection in the transition).

•GEM definitely underestimates (40% less than ISCCP) Sc cloud but overestimates about 10% shallow and deep cumulus.(more work need to be done).

SUMMARY

•GEM realistically simulates the basic structures of relative humidity except a little dry in the upper troposphere (need a preciser diagnostics from RH ---> cloud).

•GEM well simulates the zonal wind and meridional wind; also the components of the Hadley circulation including the ascending branch in the ITCZ and the descending in the mid-latitude.

•GEM simulated surface fluxes and radiation are quite close to the Observation/Reanalysis.

SUMMARY