Experiments On Tropical Circulation With A Simple Moist Model

A simple model of the circulation of the tropical atmosphere is constructed where the circulation is determined entirely by the sea surface temperature (s.s.t.) pattern, or rather by a forcing field which is closely related to s.s.t. It is an equatorial beta‐plane model with an assumed simple baroclinic vertical structure. the moisture and precipitation fields are allowed to evolve freely so there are feedbacks between the latent heating, which contributes to driving the motion, and the low‐level velocity field which produces the moisture convergence required to generate precipitation. Experiments with idealized Pacific s.s.t. distributions produce qualitatively realistic precipitation patterns for January (a patch in the west Pacific over the equator) and July (a zonal strip north of the equator). Analytic solutions for zonally symmetric flow are given to illustrate the basic dynamics and to study the parameter dependence of the precipitation. an analysis of zonal variations shows that a good simplifying approximation for this component is to neglect Rayleigh friction while retaining Newtonian cooling. The effect of changing the zonal contrast in the prescribed forcing is to gradually alter the circulation from Hadley‐like to Walker‐like. the model suggests that along the equator a relatively small contrast is needed to break a zonal band of precipitation.