Fourier Analysis of India Rainfall

Abstract

The temporal and areal distribution of monthly precipitation normal over the Indian sub-continent is studied by means of harmonic analysis. Amplitude and phase angle charts of the first three harmonics illustrate the regional boundaries for different rain patterns. The annual distribution over South India is discussed in some detail as an example of the super-imposition of the two dominating annual events which are the SW monsoon and the NE monsoon. The importance of topography on the actual amount of rainfall and its distribution under the influence of both regimes at Coondapoor and Nagercoil is described with the aid of characteristic amplitude ratios.

A secondary maximum during February is well established over the mountains of West Pakistan and Kashmir. The phase angle charts show that it is propagated in two geographic directions, from northwest to southeast along the south side of the Himalayas, and from north to south along the west side of the Baluchistan mountains. The only area where the intensity of winter rains exceeds that of summer precipitation was found to be the intermontane region of Baluchistan.