Response of an atmospheric general circulation model to radiative forcing of tropical clouds

摘要: The effects of upper tropospheric cloud radiative forcing (CRF) on the atmosphere have been examined using a recent version atmospheric general circulation model (AGCM) developed by Max Planck Institute Meteorology and University Hamburg. This reproduces satellite-observed clouds well overall, except that maxima somewhat exceed those observations. Three simulations performed where above 600 mbar rendered transparent to all radiation: first, throughout tropics in “NC” experiment; then only over oceans warmer than 25°C “NCW” finally, western Pacific warm “NCWP” experiment. local these when they are present heating middle troposphere due convergence longwave solar radiation; cooling tropical near tropopause; large reduction radiation (50 100 W/m2) reaching surface; slight increase (5 20 downward at surface. removal significantly alters atmosphere, as previous AGCM studies, showing seemingly moderate heat source such CRF is nonetheless capable widespread influence global precipitation. experiment responses include significant weakening (in NCW) or rearrangement NCWP) Walker circulation. Zonal mean cover, rainfall, low-level change modestly experiments, while zonal departures from their means shift considerably. Regions warmest which lose become much less cloudy, indicating positive feedback convection. changes diagnosed terms simple energy budget arguments, suggest importance enabled small magnitude moist transport tropics. They also response may be strongly dependent eddies interactions between surface fluxes lapse rates. itself should relatively independent interactions.