On the migration of maximum tropical rain fall zone in a simple climate model

Abstract

The aim of this thesis is to understand the seasonal migration of the maximum precipitation zone in the tropics (ITCZ) using a simple climate model. An attempt is also made to extract at least phenomenological answers to the questions:

In a simple climate model, with important feedbacks, will there be a steady?state solution under a constant solar insolation? How long will it take to arrive at a steady?state solution, if it exists? For a long?term experiment with varying solar forcing, will the climate parameters repeat exactly in time? If they do not, what type of inter?annual variations do we get? On these long time scales, which components of climate repeat and which components show inter?annual variations?

To answer these questions, a simple, zonally and vertically averaged thermodynamic energy?balance model is developed. This model uses the conservation equations of energy and moisture. The feedback mechanisms due to clouds, ice, and soil moisture are incorporated in the model. All the heat fluxes are parameterized by very simple relations. The large?scale and small?scale precipitation components are parameterized separately. The existence and non?existence of ice are determined by a threshold surface temperature. The following results are obtained:

Tropical maximum rainfall migration depends on the lower boundary. Desert regions form in both hemispheres. Various climatic parameters at the equator show inter?annual variation. A phase lag between outer?space solar radiation and temperature fields is observed. Unlike the rainfall distribution, the evaporation distribution is rather smooth. The migration of tropical maximum rainfall is associated with land processes. The migration of the ITCZ over continental regions is found to be about 30 degrees, whereas over oceanic regions the migration is less than 5 degrees.