A Simple Model of the Tropical Atmosphere with Circulation Dependent Heating and Specific Humidity

Abstract

A shallow water equations model of the tropical atmosphere is developed and tested. The model includes a simple parameterization of convective rainfall so that the model heating is a function of fixed sea surface temperatures and model dependent circulation. To achieve quasi-steady states the model is iterated a number of steps. For equatorial sea temperature perturbations imposed on an idealized Pacific Ocean, the model shows two distinct modes of response. In one mode local evaporation is slightly more important than moisture convergence. This results in a relatively weak, equatorially trapped perturbation circulation. In the other mode moisture convergence is dominant and the associated circulation is stronger and less equatorially trapped. The necessary condition for the second ?enhanced? mode is that the positive sea temperature perturbations overlap sufficiently with the climatologically warm waters of the western ocean. Subtropical sea temperature perturbations generally result in a steady state heating with a relatively broad meridional scale and moderate magnitude. The final states are relatively insensitive to the position of the sea temperature perturbations relative to the mean sea temperature field. While these results must be viewed as quite preliminary due to the simple nature of the dynamical model, they do suggest that actual atmospheric heating perturbations may be the result of complex interactions between oceanic and atmospheric conditions by way of both the surface evaporation and moisture convergence processes.