Surface Wind Vergence over the Tropical Indian Ocean

Abstract

From surface wind estimates published in the Dutch Atlas monthly charts of surface wind vergence over the Indian Ocean down to 50S were computed. Since the original data were smoothed by a low-pass filter, the charts exhibit only regional and large-scale features. The vergence distributions are not zonally symmetric; rather, they show a cell-like structure. The vergence patterns are discussed in terms of latitudinal-time sections, both for the Arabian Sea and the Bay of Bengal longitude range, and compared with similar plots of the precipitation frequency. North of 10–20S there seem to exist three different circulation regimes, separated by sharply defined transition periods, a characteristic of the Indian monsoon climate. A simple description of this threefold monsoonal rhythm is given in terms of the first and second harmonies of the annual march of temperature.