Thunderstorm frequency distribution and associated convective mechanisms over Pakistan

Abstract

This study investigates the frequency distribution of thunderstorm activity over Pakistan via the analysis of two convective parameters, i.e., convective available potential energy (CAPE) and convective inhibition (CIN). The climatology and trends of thunderstorm frequency, CAPE, and CIN have been analyzed, based on seasonal and annual timescales, by using station and reanalysis datasets. Thirty-eight years (1979–2016) data of monthly thunderstorm days for 54 meteorological stations, well-distributed over the country, have been utilized in this study. Those meteorological stations which constitute core region of thunderstorm frequency are identified. Our analysis showed that the mountainous and sub-mountainous areas of Pakistan, particularly in upper half of the country, are at the top with the maximum thunderstorm activity on both seasonal and annual timescales. Pre-monsoon (April–June) and monsoon (July–September) are most vulnerable seasons to the development of thunderstorms. It is also observed that most of the stations exhibit an increase in the thunderstorm days during winter (December–March) and decrease during pre-monsoon, monsoon, and post-monsoon (October–November) seasons. Interestingly, core regions of CAPE and thunderstorm frequency almost coincide with region of low CIN. However, trends in CAPE do not explain the variability and trends of thunderstorm frequency over the whole study area explicitly. At some stations, trends in CAPE are increasing in contrast to thunderstorm frequency trends. We showed, in particular, that the increasing trend of CIN is a likely reason for decreasing trends of thunderstorm frequency over Pakistan. In total, 17 stations are identified to be the most vulnerable to thunderstorm activity over the country.