Large-scale circulation and heat sources over the Tibetan Plateau and surrounding areas during the early summer of 1979, Pt. 2, Heat and moisture budgets

The large-scale heat and moisture budgets over the Tibetan Plateau and surrounding areas during a 40-day period from late May to early July 1979 are studied by using the FGGE level 2-b data. During this period, the general circulation over East Asia underwent a distinct seasonal change characterizing the onset of the summer monsoon circulation. The analyses of the horizontal distributions of the vertically integrated heat source and moisture sink reveal the major heat source regions and their different degrees of association with precipitation. The 40-day mean distributions show intense heat sources of 150-300 W m super(-) super(2) , with moisture sinks of nearly equal magnitude over the Assam-Bengal region and in a broad belt extending over the China Plain along the mei-yu front. The heat source of similar to 100-150 W m super(-) super(2) over the eastern Tibetan Plateau is accompanied by a moisture sink with a magnitude about half as large. The heat sources over the western plateau and the Takla Makan Desert are not accompanied by appreciable moisture sinks. The heat sources over the plateau are pronounced in the upper troposphere. The mean heating rate of similar to 3 K day super(-) super(1) in the 200-500-mb layer above the eastern Plateau is as intense as that over the Assam-Bengal region. Examination of the daily vertical profiles of the areal mean heat source and moisture sink shows distinct differences in the heating process and its time changes over the western plateau and adjacent areas (Region 1), the eastern plateau (Region 2), the Yangtze River (Region 3), and the Assam-Bengal region (Region 4). In Regions 1 and 2, heating in the troposphere is seen prior to the onset of the summer rains. The heating in Region 2 intensifies with the progress of the rain season. The heating in Region 3 is due primarily to frontal rains, and that in Region 4 is due to highly convective monsoonal rains. In Region 1, the mean sensible heat flux at the surface during the pre-onset period is similar to 170 W m super(-) super(2) , while in Region 2, the mean sensible heat flux for the total period is similar to 105 W m super(-) super(2) . The corresponding values of the condensation heating are similar to 10 and similar to 70 W m super(-) super(2) , respectively. The estimated mean evaporation rates on the plateau for the total period are similar to 1 mm day super(-) super(1) . These estimates compare well with the June mean values obtained by Yeh and Gao from surfac