Indian rainfall in relation to the sunspot cycle: 1871-1978

Abstract

The paper presents the results of a detailed study of the annual rainfall of India in relation to the sunspot cycle for the period 1871 to 1978. Rainfall time series of individual stations as well as of meteorological subdivisions have been examined for the full period (108 years) and for two half periods.The correlation coefficients (CC) of 306 stations for the full period lie between 4-0-29 and -0-14 with a preponderance of positive over negative values in the ratio 4:1. Twenty-six CC values are significant at the 5 per cent level. The CC values for the two subseries reveal appreciable temporal variations, the correlations being higher for the first half. Lag correlations between the rainfall and sunspot series indicate that the CC values tend to increase when the rainfall is correlated with sunspot numbers 1 to 3 years later and to decrease when correlated with sunspot numbers 1 to 3 years earlier.Examination of the all-India rainfall series and the sunspot series for the full period shows that excess rainfall years were significantly more during the ascending phase of alternate cycles. Superposed epoch analysis and the Student t test show that the rainfall around the maximum of even cycles characterized by high sunspot activity is significantly higher than the corresponding rainfall in the odd cycles with lesser spot activity. Correlation study with a 15-year sliding window reveals large temporal variations in the CC values.Although most of the variance in the rainfall time series is due to causes unconnected with the sunspot cycle, the present study suggests the existence of a weak positive association between Indian rainfall and sunspots on the 22-year time scale, although the causal connection is unknown.