Extreme Indian Monsoon Rainfall Years and the Sunspot Cycle

摘要

The objective of the present study is to examine the predictability of extreme Indian rainfall years. The all-India rainfall and recently defined spectrally homogeneous region (SHR7) are studied in relation with negative of second derivative (represented as -S_m'') of annual sunspot numbers for the period 1871-2005. We argue that SHR7, which includes sub-divisions from west central and peninsular India, may be more appropriate rainfall index in compare to all-India for such analysis. It is shown that SHR7 shows more symmetric relation when predicting excess and deficit rainfall years in relation with -S_m", than all-India rainfall. Examination of the SHR7 rainfall and the -S_m", shows that all the maxima of even sunspot cycles coincide with excess rainfall (with +1 year error) and all the minima of odd sunspot cycles coincide with deficit rainfall (with ±2 year error). Also probability of excess rainfall at or around the -S_m'', maxima is calculated as 0.82 and that of deficit rainfall with -S_m'' minima is 0.75. Respective probabilities for All-India data are 0.64 and 0.5.