资源环境科技发展态势分析平台

The effect of partial cloudiness is included in a cloud microphysics scheme, and its impact on precipitation processes is examined through global-model simulations for a boreal summer. An excessive precipitation rate in the simulations is reduced by considering the partial cloudiness effect in microphysical processes, especially in the tropical western Pacific region where convective activity is strong. The reduction of the precipitation rate in this region is mainly due to a decrease in convective precipitation, as the partial cloudiness effect in cloud microphysical processes modulates the convective activity by interacting with radiative processes. Cloud radiative forcings are weaker in the simulations including the partial cloudiness effect, as more cloud water and ice are converted to rain and snow mainly due to enhanced accretion rates. This leads to a decrease in cloud radiative forcing for both shortwave and longwave fluxes, which is overestimated overall over the ocean in the simulations. Temperature is lowered overall as increased longwave radiative cooling overcompensates increased shortwave radiative heating. This reduces the convective available potential energy and results in a decrease in convective precipitation. The weakened instability and upward motion over the tropical western Pacific region due to the partial cloudiness effect not only affect the local precipitation processes in this region but also suppress the downward motion over the tropical eastern Pacific regions by modulating the large-scale zonal circulation over the tropical Pacific ocean.