LAUSR

Thunderstorms are one of the most devastating mesoscale severe weather phenomena, which play an important role in the occurrence of rainfall activity over a region. Therefore, in the present study an attempt has been made to identify the relationship between thunderstorm days (Thn), rainy days (Thr) and rainfall amounts (Trr) for 294 meteorological stations spreading over India, by means of published data (climatological normals) from the India Meteorological Department (IMD) for four periods, 1951-1980, 1961-1990, 1971-2000, and 1981-2010. The analysis has revealed a sharp decrease in the frequency of Thn, while Thr and Trr showed a slight decline. A significant correlation between Thn, Thr and Trr has been observed. Monthly analysis has exhibited a dual peak in the occurrence of Thn and single peak in rainfall activity; however, a time lag of one month in their peak occurrence was detected. These results show that the Indian summer monsoon affects significantly the thunderstorm activity over India. Seasonal analysis suggests that Thn, Thr and Trr are maximum during the monsoon season, while minimum during winters. Apart from this, Thn and Thr, and Thn and Trr have demonstrated a negative relationship during the monsoon, which may be anomalously due to decreasing temperature in India during that season. In addition, the spatial annual and seasonal pattern of the occurrence of Thn, Thr and Trr shows almost a similar pattern during 1951-1980. However, a sharp decline in the frequency of Thn has been observed during subsequent periods over all parts of the country. Likewise, a slight decline in the frequency of Thr and Trr has been observed over India, except in the northeast, where an increasing trend in rainfall activity has been observed. The computed ratio between Thn and Thr (R) has been found maximum during the pre-monsoon, whereas the ratio between Trr and Thn (RTR) during the monsoon season. Regional analysis of Thn, Thr and Trr revealed a wide range of variations in the occurrence of these parameters month after month. It is believed that the results presented in this study will be useful for weather forecasters, aircraft pilots, agriculturists and planners.