A simple model of the tropical intraseasonal oscillation

Abstract

The tropical intraseasonal oscillation is studied by use of a simple model based on a CISK mechanism.In this model, the CISK parameter is chosen to be large over areas of high sea surface temperature (SST) distribution in order to describe the high convective activity that occurs in those regions.The unstable disturbance generated in the regions of high convective activity (high SST) grows as it moves eastward.The disturbance has a baroclinic structure and its horizontal pattern consists of a combined Kelvin and Rossby type response.As the unstable disturbance propagates to the less convectively active regions (low SST), it decays with time, generating free waves by dispersion.These free waves propagate further eastward to eventually become one of the sources of the next unstable disturbance generated in the convectively active region.It is shown that the tropical intraseasonal oscillation can be interpreted as a pulsation induced by the repetition of this process.