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

Based on the latest data (I. M. D., 1999) of mont hly number of station thunderstorm days (Thn) and mean maximum surface air temperatures ( Tmax) of 276 Indian stations, an important and a long p ending issue of eastwest contrast in the frequencies of occurrence of thunde rstorms over India is resolved in substantial detai ls in this study. On the premise of nearly equal land areas, and density of the station network, and location of ITCZ; Indi a is divided in two regions: Eastern Region (ER) and Western Region (WR ) across the 79° E longitude line over India. Resul ts pertaining to the contrasting features of Thn over ER and WR are presented. Our analysis showed that the annual tota l Thn over the ER are 4763, and over the WR are 3194 and the prominen t difference in Thn is associated with monsoon seas on months over the ER and WR. The temperature sensitivity of occur rence of Thn showed that thunderstorms respond expo n ntially to modest increment in Tmax 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 agreeme nt with the results cited in many studies, where re lationship between global tropical surface air temperatures and GEC pa rameters are investigated. Our analysis suggests th a the hot and humid extensive land region of the ITCZ of the ER i s more suitable and responsible for the development of thunderstorms. Further, results showing higher valu es of CAPE and moisture field over the ER are discu s ed to explain the E-W pronounced contrast in the thunderstorm act ivity. It is believed that the results presented in this study will be useful.