Thunderstorm activity over India and the Indian southwest monsoon

Abstract

This paper describes the results of monthly latitudinal (8°–30°N) and latitude belts (8° –10°, 10° –15°, 15° –20°, 20° –25°, and 25° –30° N) averaged seasonal thunderstorm activity over India by using monthly data from a large number of Indian stations from 1970 to 1980. The latitudinal variation in the premonsoon (March‐April‐May) and monsoon season (June‐September) months is described and the results are discussed. An examination of the seasonal thunderstorm day activity in the first four belts indicated systematic changes in their signals of semiannual oscillation. These changes are noted to be a function of latitude and season and appear to be consistent with the seasonal migration of the Intertropical Convergence Zone and solar heating of the Indian landmass. We compare the thunderstorm day activity with the monthly mean maximum values of the surface wet‐bulb (Tw) temperatures in the five latitude belts over the Indian region. By using rainfall data for the same period of study, the relationship between seasonal rainfall and number of thunderstorm days over the 11 year period is examined. The results of variation of the ratio of monthly rainfall to thunderstorm days (RTR) during different phases of the southwest monsoon are also presented. Results of the monthly mean electrical conditions of mesoscale and isolated deep convective storms at Pune are summarized. It is noted that the electrification of the premonsoon season thunderstorms dominated by a factor of 3–4 over the monsoon ones. We have examined at length the possible influence of the El Nino on the occurrence and electrification of thunderstorms over the Indian region.