Numerical simulation of the Indian summer monsoon

Abstract

A simplified model of zonally symmetric motion in the two-dimension has been formulated to simulate the monsoon circulation. The atmosphere from the surface upto the top has been divided into nine levels for which temperature, water vapour and velocity components are predicted. The final solution is obtained as the asymptotic steady state of an initial value problem solved by a marching process.

To start with, the atmosphere was assumed to be at rest. As time progressed, winds slowly developed. After 80 days, the simulated circulation was fully developed, as normally observed, with westerlies in the lower levels and easterlies aloft. The easterly jet had a core speed of 35 m/sec. The meridional circulation showed southerlies near the surface and northerlies at higher levels.

The circulation was found to become weak when the presence of the Himalayas was disregarded. The upper-level easterlies reached a maximum speed of hardly 8 m/sec. Neglect of moisture in the model did not affect the monsoon circulation, although its presence was essential for the occurrence of rainfall. On the whole, the results bring out the Importance of thermal and dynamical influence of the Himalayas Upon the generation and the development of the monsoon circulation.