A Simple-Model of the Climatology and Variability of the Low-Level Wind-Field in the Tropics

A simple model of the low-level wind field in the entire tropics is presented. The dynamics are the same as those within the familiar Gill model, i.e., linear, steady state, contained within a single vertical mode and damped by Rayleigh friction. Convective atmospheric heating can occur if a lifted air parcel is buoyant relative to its surroundings, and the heating is computed with reference to the cloud model of Yanai et al. Radiative cooling is represented by a Newtonian cooling to an equilibrium lapse rate. The model is forced by surface temperature and humidity. A qualitatively correct representation of the climatological flow is achieved. The main differences between model and observations relate to the model's inability to reproduce the intensity and limited spatial scale of the convergence zones. Model simulations of anomalous circulations are subject to the same limitations. Problems related to the lack of an explicit boundary layer in the model, the poor representation of radiation, and the cumulus parameterization are discussed, together with suggestions for future work.