THE ROLE OF CLOUDE/RADIATION IN LONG-RANGE NUMERICAL WEATHER PREDICTION

We investigate the role of clouds and radiation in the general circulation of the atmosphere usinga model designed for 30-day predictions.Comprehensive verifications of 30-day predictions for the 500 hPa geo-potential height field have been carried out,using the data from ECMWF objective analyses that cover theperiod from May 5 to June 3,1982.We perform three model simulations,including experiments with interac-tive cloud formation,without clouds,and without radiative heating.The latter two experiments allow us tostudy the effects of cloud/radiation interactions and feedbacks on the predicted vertical velocity,and themeridional and zonal wind profiles,averaged over a 30-day period.We demonstrate that the Hadley circulation is maintained by the presence of clouds.The radiative coolingin the atmosphere intensifies the vertical motion in low latitudes and,to some extent,also strengthens theoverall meridional circulation.The meridional winds are correctly reproduced in the model if clouds areincorporated.The zonal winds are significantly affected by clouds and radiative cooling.Without an appropriate incor-poration of these physical elements,the model results would deviate significantly from observations.Thepresence of clouds strengthens the westerlies in middle and high levels.In May,the northerly movementof the jet stream over eastern Asia is,in part,associated with the presence of clouds.