Observational study of the monsoonal dynamics and eddy shedding phenomena

Abstract

We analyze atmospheric data in order to study the upper tropospheric dynamics in the area of the Asian summer monsoon. We look at summers of four years from 1987 to 1990. The divergent upper tropospheric circulation of the monsoon often adopts the form of a unified large-scale vortex. However, when the vortex becomes elongated enough, so that the flow in most of the area is close to zonal, the vortex usually sheds secondary, or daughter, vortices that then propagate away. Eddy shedding occurs in all four summers that we examined. We use the potential vorticity and Montgomery stream-function fields to document the characteristics of eddy shedding events. In most cases, the daughter cell propagates westward. In the vertical, eddy shedding is confined to the upper troposphere, between 300 and 100 mb. The relationship between lower convergent and upper divergent levels is strong. However, we have not found any simple relationship between eddy shedding and lower-level dynamics.