Regional Energetics of the 200 mb Summer Circulations

Abstract

Some of the characteristic features of the summer monsoon circulation are investigated using 200 mb wind data operationally determined by the National Meteorological Center during three summers (1970?72). Three-year summer mean 200 mb divergence was large near India, Japan and the Philippines, three of the most actively convective regions during the summer monsoon. A pronounced 200 mb anticyclone lay centered over north India, while the 200 mb velocity potential outflow center was located near the Philippines with a prominent north?south overturning, vertical circulation along 125°E. The intensity and location of the 200 mb anticyclone changed substantially from one monsoon season to the other. Little change was observed in the location of the primary 200 mb velocity potential outflow center. The energy equation was applied to specific limited regions to investigate the effect of boundary fluxes and barotropic processes upon area-averaged eddy kinetic energy during summer. Area-averaged 200 mb zonal mean flows are barotropically unstable over the subtropical North Pacific, the South China Sea-Indonesia region and the tropical South Indian Ocean. Over Indonesia and the South Indian Ocean, the upper zonal mean flows were substantially more barotropically unstable in 1972 than in 1970 or 1971. This is contrasted with exceptionally stable 200 mb zonal mean flows in summer 1972 near India where the monsoon rains were abnormally weak.