Abstract:
We use 130 years data for studying correlative effects due to solar cycle and activity phenomena on the occurrence of the Indian Monsoon rainfall. We compute the correlation coefficients and significance of correlation coefficients for the seasonal and the annual data. We find that: (i) for the whole years 1871-2000, the spring and southwest monsoon rainfall variabilities have significant positive correlations with the sunspot activity during the corresponding period, (ii) the FFT and the wavelet analyses of the southwest monsoon rainfall variability show the periods 2.7, 16 and 22 year, respectively (similar to the periods found in sunspot occurrence data) and, (iii) there is a long-term trend indicating a gradual decrease of occurrence of rainfall variability by nearly 2.3+/-1.3 mm/year and increase of sunspot activity by nearly 3.9+/-1.5 sunspots/year compared to the activity of previous solar cycle.
We speculate in this study a possible physical connection between the occurrence of the rainfall variability and the sunspot activity, and the flux of galactic cosmic rays. Owing to long-term positive and significant correlation of the spring and southwest monsoon rainfall variabilities with the sunspot activity, it is suggested that solar activity may be included as one of the crucial parameter in modeling and predicting the Indian monsoon rainfall.
