EFFECTS OF RADIATION SCHEME ON THE SURFACE TEMPERATURE AND WIND OVER THE ANTARCTIC AND ON CIRCUMPOLAR LOWS

We have examined effects of radiation schemes including cloud emissivity on the surface temperature and wind over the Antarctic in May by performing one month integration of a global spectral model of the Meteorological Research Institute. It is found that radiation schemes have large effects on the surface and surface air temperatures; increase in longwave downward flux due to the improvement of radiation scheme directly results in temperature rises of surface and surface air. Above all, clouds play a crucial role in determining the surface temperature. When clouds are treated as non-black bodies, the surface temperature lowers through decrease in longwave downward flux. The surface temperature is found to be highly correlated to the surface pressure. When the surface temperature over the Antarctic rises, the surface pressure also rises, and the circumpolar lows move northward while weakening. It is also shown that in the Antarctic the surface air is subject to large cooling owing to radiation and heat exchange with the cold surface; however, the cooling is compensated for by heating by adiabatic compression in down draft process and entrainment of upper warmer air. Surface wind speed is to a great degree affected by surface temperature, while surface wind direction is nearly independent of surface temperature