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Spatio-Temporal Variations of Thermodynamic Indices during Pre-Monsoon Season Thunderstorms over Eastern India
  • Rajesh Kumar Sahu,
  • Bhishma Tyagi
Rajesh Kumar Sahu
National Institute of Technology Rourkela, India

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Bhishma Tyagi
National Institute of Technology Rourkela
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Thunderstorms are very violent and short-lived weather phenomena associated with thunder, rain, heavy wind, lightning and dense clouds. These storms are persistent and intense during the pre-monsoon (March-May) season over Eastern and North-eastern India, leading to catastrophic destruction over the regions. These thunderstorms are locally known as Kal-Baishakhi, Bordoichila or Nor’westers, which are short-lived events able to make changes in the thermodynamic properties of the environment. In this work, thermodynamic indices were calculated and analysed to evaluate the spatial and temporal variations of thunderstorms over Eastern India (Odisha, Jharkhand and West Bengal). The present study also investigated the influence of climate change on thermodynamic indices thresholds over Eastern India by using radiosonde data and ERA-5. The thermodynamic indices considered in the study are Boyden index, bulk Richardson’s number, convective available potential energy, convective inhibition, cross totals index, dew point temperature at 850hPa, humidity Index, K index, lifted index, relative humidity at 700hPa, Showalter index, severe weather threat index, total totals index, vertical totals index. After calculating these indices, with the information of thunderstorm occurrence over the region, skill score analysis has been accomplished based on the contingency table. The work discussed the change in the thermodynamic indices pattern with every 5-year interval time for temporal variations and the climatological variation of thermodynamic indices by using spatial plots to differentiate the thunderstorm and non-thunderstorm days for spatial variations. In the temporal variation, some thermodynamic indices show a noticeable shift of threshold values over time, while some indices do not exhibit any apparent change in the pattern. The trend analysis of these thermodynamic indices shows evident changes in trends over the different regions of Eastern India for thunderstorm and non-thunderstorm days. Keywords: Thunderstorm, Climate Change, Thermodynamic indices, Radiosonde data, Skill score