Morphological classification pertaining to validate the climatology and category of thunderstorms over Kolkata, India

Abstract

Devastation due to thunderstorms ensues every year during the pre-monsoon months of April and May over Kolkata (22°32′ N, 88°20′ E), India. Such thunderstorms emerge from large vertical extent of cumulonimbus cloud and are associated with high speed wind squall, at times, exceeding 100 km h−1, deadly lightning flashes and heavy rainfall. The analyses of 102 such thunderstorms have been carried out in this study for morphological classification of thunderstorms over Kolkata, India, during the pre-monsoon season with bulk Richardson number and Byers and Braham theory of 0–6 km wind shear. The result reveals that according, to bulk Richardson number, 85 multicell and 17 supercell thunderstorms, whereas according to Byers and Braham theory, 33 single-cell, 59 multicell and 10 supercell thunderstorms prevailed over Kolkata during the period from 1997 to 2008 in the pre-monsoon season. The coupling of the two approaches together lead to classify the thunderstorms of Kolkata during the pre-monsoon season in two categories: super- and multicell thunderstorms. The result reveals that, out of 102 thunderstorms during the period from 1997 to 2008 in the pre-monsoon season, only 4 are of supercell category and the rest of 98 thunderstorms are of multicell category, depicting the dominance of multicell thunderstorms over Kolkata in the pre-monsoon season. The stability indices and other meteorological parameters are computed and compared for both the categories to identify the threshold ranges pertaining to reveal the climatology and to assess the predictability of both the categories. The result is validated with the observations of India Meteorological Department and Doppler Weather Radar imageries for the years 2009, 2010, 2011, and 2012.