The Dynamics of the Monsoon Anticyclone—a Single-Layer Model Study

The potential importance of the Asian monsoon anticyclone to the stratosphere, transport and climate motivates a reinvestigation of the corresponding dynamics and controlling processes. Many explanations for the monsoon anticyclone are based on the Gill/Matsuno theory for tropical circulations, in which the spatial structure is determined by linear momentum damping. However, the assumption of such a large scale friction process in the upper troposphere and stratosphere is often thought as questionable or even unrealistic and hence other processes must be involved. Many aspects of the anticyclone can be conveniently studied in a single-layer model, with the upper-level effects of the monsoon convective heating represented as a prescribed local mass source. Such a model is used to investigate the effects of various dynamical processes on the time and space structure of the anticyclone, including (i) the time dependent response to a steady mass source, (ii) the effect of a background flow, (iii) the effect of thermal damping and (iv) the effect of stirring of the subtropics by extratropical baroclinic eddies. Each of these can potentially change the spatial structure and time evolution of the anticyclonic circulation. This work is intended to be relevant to understanding differences between models in their representation of the monsoon anticyclone and also how the monsoon anticyclone might change in the future.