ROLE OF CONVECTIVE SCALE MOMENTUM TRANSPORT IN CLIMATE SIMULATION

This paper studies the effect of convective-scale momentum transport i n climate simulation using a comprehensive parameterization scheme. A unique feature of the scheme is the inclusion of the perturbation pres sure field induced by convection and its effect on the cloud momentum transport. Through two experiments of seasonal simulations, it is show n that the perturbation pressure forcing on the cloud momentum transpo rt accounts for a significant part of the total convective momentum so urce/sink, indicating that the cloud momentum field is substantially m odulated by the convection-induced pressure field. The overall effect of convective momentum transport is to reduce the vertical wind shear in both the zonal and the meridional directions. The response of the l arge-scale circulation to convective momentum transport is very signif icant. The zonally averaged zonal wind decreases by as much as 5 ms(-1 ) in a broad area in the upper tropical troposphere and the midlatitud es of the winter hemisphere. The Hadley circulation becomes stronger a s a result of the zonal momentum transport. In general, inclusion of c onvective momentum transport leads to a much better simulation of the wind fields in both the upper and the lower troposphere. The temperatu re and moisture changes as a result of the inclusion of convective mom entum transport are also examined in this study. The tropical troposph ere is warmer and more moist due to the enhanced Hadley circulation. H owever, considering the uncertainties of the climatological analyses, most of these thermodynamic changes only make marginal improvement to the simulation.