Climatology of thunderstorm activity over the Indian region : A study of east -west contrast

Abstract

Based on the latest data (I. M. D., 1999) of monthly number of station thunderstorm days (Thn) and mean maximum surface air temperatures (T_max) of 276 Indian stations, an important and a long pending issue of east- west contrast in the frequencies of occurrence of thunderstorms over India is resolved in substantial details in this study. On the premise of nearly equal land areas, and density of the station network, and location of ITCZ; India is divided in two regions: Eastern Region (ER) and Western Region (WR) across the 79° E longitude line over India. Results pertaining to the contrasting features of Thn over ER and WR are presented. Our analysis showed that the annual total Thn over the ER are 4763, and over the WR are 3194 and the prominent difference in Thn is associated with monsoon season months over the ER and WR. The temperature sensitivity of occurrence of Thn showed that thunderstorms respond exponentially to modest increment in T_max on the semi-annual and annual time-scales in both the regions but with clear contrast in their sensitivity over ER. This result is in good agreement with the results cited in many studies, where relationship between global tropical surface air temperatures and GEC parameters are investigated. Our analysis suggests that the hot and humid extensive land region of the ITCZ of the ER is more suitable and responsible for the development of thunderstorms. Further, results showing higher values of CAPE and moisture field over the ER are discussed to explain the E-W pronounced contrast in the thunderstorm activity. It is believed that the results presented in this study will be useful.