Heat and moisture budgets over China during the early summer monsoon

Synoptic sounding and surface data are used to calculate heat sources and moisture sinks over China during the pre-Meiyu and Meiyu periods of 1987, 1988 and 1989. The horizontal distributions of the vertically integrated heat source <Q₁> and moisture sink <Q₂> show that during the pre-Meiyu, the maximum heating is located in southern China in a band parallel to the coastline with a secondary maximum over the Yangtze Valley. When the Meiyu sets in, there is an increase in the heating in the Yangtze region; however, a band of heating continues over southern China during the Meiyu. In 1988 there is a prominent third band of heating over northern China. There is pronounced diurnal variation in rainfall during both the pre-Meiyu and Meiyu periods due to land/sea and mountain/valley breezes. At night, maximum rainfall occurs at lower elevations in the prominent basins of interior China. During the day, rainfall maxima shift to the region between the coast and the coastal mountain ranges and other areas favored by upslope flow. The vertical profiles of the heat source Q₁ and moisture sink Q₂ averaged over subregions of China show that during both the pre-Meiyu and Meiyu, the precipitation type over the Yangtze region is a mixture of convective and stratiform, whereas over southern China deep cumulus convection predominates. The heating and drying in southern China occur throughout the whole troposphere, but low-level moistening occurs in the Yangtze region. The pattern in southern China resembles that observed in the deep tropics, whereas that in the Yangtze region is similar to that observed with midlatitude mesoscale convective systems where low-level evaporation is important.