A NUMERICAL EXPERIMENTAL STUDY OF SOME DYNAMICAL EFFECTS ON SOUTHERN ASIATIC HIGH

Using a barotropic, steady and linearized vorticity equation and using 250 hPa observed basic flow and global divergence field from the active summer monsoon phase (00 GMT 26 June－12 GMT 29 June) 1979, the dynamical effects of linear absolute vorticity advection, vorticity generation due to divergence and vorticity dissipation due to frictional damping have been tested to understand their influence on Southern Asiatic High (SAH). The key experimental results are: (1) The SAH, one of the major planetary-scale disturbances, is generated from the upper basic flow by the forcing of the upper tropospheric divergence over southeast Asia during the active summer monsoon phase. (2) Linear absolute vorticity advection and frictional damping of vorticity play an important role in the determination of the location of the SAH. (3) The destruction and recovery of planetary-scale geostrophic balance is an important mechanism for the west-east oscillation of the SAH.