An analysis of thermally-related surface rainfall budgets associated with convective and stratiform rainfall

摘要

Both water vapor and heat processes play key roles in producing surface rainfall. While the water vapor effects of sea surface temperature and cloud radiative and microphysical processes on surface rainfall have been investigated in previous studies, the thermal effects on rainfall are analyzed in this study using a series of two-dimensional equilibrium cloud-resolving model experiments forced by zonally-uniform, constant, large-scale zonal wind and zero large-scale vertical velocity. The analysis of thermally-related surface rainfall budget reveals that the model domain mean surface rain rate is primarily associated with the mean infrared cooling rate. Convective rainfall and transport of hydrometeor concentration from convective regions to raining stratiform regions corresponds to the heat divergence over convective regions, whereas stratiform rainfall corresponds to the transport of hydrometeor concentration from convective regions and heat divergence over raining stratiform regions. The heat divergence over convective regions is mainly balanced by the heat convergence over rainfall-free regions, which is, in turn, offset by the radiative cooling over rainfall-free regions. The sensitivity experiments of rainfall to the effects of sea surface temperature and cloud radiative and microphysical processes show that the sea surface temperature and cloud processes affect convective rainfall through the changes in infrared cooling rate over rainfall-free regions and transport rate of heat from convective regions to rainfall-free regions.