The solar influence on the monsoon rainfall over Tamil Nadu

We use 100 years data for studying correlative effects between solar cycle and rainfall over Tamil Nadu. For the period of different solar cycles, we compute the correlation coefficients for the seasonal months of Jan-Feb (JF), Mar-May (MAM), June-Sept (JJAS) and Oct-Dec (OND) and annual mean data. We find that: (i) with a moderate -to high significance; Tamil Nadu rainfall is correlated with the sunspot activity and (ii) there is an overall trend that during the period of high sunspot activity, occurrence of rainfall is low compared to the period of low sunspot activity. We speculate in this study a possible physical connection between the occurrence of the rainfall and the sunspot activities and the flux of galactic cosmic rays. Some of the negative correlations between the occurrences of the sunspot and rainfall activities obtained for different solar cycle periods are interpreted as effects of aerosols on the rain forming clouds due to either intermittent volcanic eruptions or due to intrusion of interstellar dust particles in the earth's atmosphere.