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Tropical Rainfall Diurnal Cycle in a 20km-mesh Atmospheric GCM

Tropical Rainfall Diurnal Cycle in a 20km-mesh Atmospheric GCM

Akio Kitoh and Osamu Arakawa
Meteorological Research Institute, Tsukuba, Japan
kitoh@mri-jma.go.jp

Tropical rainfall diurnal variation simulated by 20km-mesh atmospheric GCM (GCM-TL959) and its lower-resolution version (190km-mesh GCM-TL95) are investigated by comparing with the Tropical Rainfall Measuring Mission(TRMM) 3G68 V6 data. Both GCMs were integrated for 10 years after spin-up with the observed monthly mean sea surface temperature (SST) and sea ice distribution climatology. For annual mean rainfall diurnal cycle, diurnal rainfall amplitude in GCM-TL959, defined by peak to-trough rainfall difference, is larger than that in TRMM 3G68 data over both land and the ocean. The local time of maximum rainfall in GCM-TL959 is 1-2 hour earlier than that in TRMM 3G68 data over both land and the ocean. However, there are large differences in simulated peak time with the TRMM 3G68 data over some region such as the southern slope of the Himalayas and Congo basin, equatorial Africa. Comparison between GCM-TL95 and GCM TL959 shows little difference both diurnal phase and amplitude. These results show that spatial resolution has little impact on simulation of rainfall diurnal cycle in GCMs and indicate importance of parameterization for physical processes.