Role of monsoon zonal flow on CISK instability and vice-versa—A sensitivity study

Abstract

In order to study the effect of inclusion of idealized monsoon now on the stability characteristics, structures and energetics of the unstable modes arising due to the conditional instability of second kind (CISK) and vice-versa, a modified equatorial balance model of Murakami is executed with 7 different combinations of basic state parameters. The most important instability characteristics observed in the analysis are that (i) The unstable modes arising from the basic flow did not show much change in their characteristics with the introduction of CISK in the basic state; however, introduction of zonal flow modified the growth rate, phase speed and vertical structure of CISK mode unstable disturbances, and (ii) from the energetics study it is understood that the barotropic instability plays a dominant role, whereas baroclinic instability plays a stabilizing role for the unstable modes.