Atmospheric diabatic heating and summertime circulation in Asia-Africa area

Utilizing data from NCEP / NCAR reanalysis, the summertime atmospheric diab atic heating due to different physical processes is investigated over the S ahara desert, the :Tibetan Plateau, and the Bay of Bengal. Atmospheric circ ulation systems in summer over these three areas are also studied. Thermal adaptation theory is employed to explain the relationship between the circu lation and the atmospheric diabatic heating. Over the Sahara desert, heating resulting from the surface sensible heat fl ux dominates the near-surface layer, while radiative cooling is dominant up ward from the boundary layer. There is positive vorticity in the shallow bo undary layer and negative vorticity in the middle and upper troposphere. Do wnward motion pre vails over the Sahara desert, except in the shallow near- surface layer where weak ascent exists in summer. Over the Tibetan Plateau, strong vertical diffusion resulting from intense surface sensible heat flu x to the overlying atmosphere contributes most to the boundary layer heatin g, condensation associated with large-scale ascent is another contributor t o the lower layer heating. Latent heat release accompanying deep convection is critical in offsetting longwave radiative cooling in the middle and upp er troposphere. The overall diabatic heating is positive in the whole tropo sphere in summer, with the most intense heating located in the boundary lay er. Convergence and positive vorticity occur in the shallow near-surface la yer and divergence and negative vorticity exist deeply in the middle and up per troposphere. Accordingly, upward motion prevails over the Plateau in su mmer, with the most intense rising occurring near the ground surface. Over the Bay of Bengal, summertime latent heat release associated with deep conv ection exceeds longwave radiative cooling, resulting in intense heating in almost the whole troposphere. The strongest heating over the Bay of Bengal is located around 400 hPa, resulting in the most intense rising occurring b etween 300 hPa and 400 hPa, and producing positive vorticity in the lower t roposphere and negative vorticity in the upper troposphere. It is also show n that the divergent circulation is from a heat source region to a sink reg ion in the upper troposphere and vice versa in lower layers.