Abstract
Thunderstorms of pre-monsoon season (April – May) over Kolkata (22° 32’N, 88° 20’E), India are invariably accompanied with lightning flashes, high wind gusts, torrential rainfall, occasional hail and tornadoes which significantly affect the life and property on the ground and aviation aloft. The societal and economic impact due to such storms made accurate prediction of the weather phenomenon a serious concern for the meteorologists of India. The initiation of such storms requires sufficient moisture in lower troposphere, high surface temperature, conditional instability and a source of lift to initiate the convection. Convective available potential energy (CAPE) is a measure of the energy realized when conditional instability is released. It plays an important role in meso-scale convective systems. Convective inhibition energy (CINE) on the other hand acts as a possible barrier to the release of convection even in the presence of high value of CAPE. The main idea of the present study is to see whether a consistent quantitative range of CAPE and CINE can be identified for the prevalence of such thunderstorms that may aid in operational forecast. A statistical – fuzzy coupled method is implemented for the purpose. The result reveals that a definite range of CINE within 0 – 150 Jkg-1 is reasonably pertinent whereas no such range of CAPE depicts any consistency for the occurrence of severe thunderstorms over Kolkata. The measure of CINE mainly depends upon the altitude of the level of free convection (LFC), surface temperature (T) and surface mixing ratio (q). The box-and-whisker plot of LFC, T and q are drawn to select the most dependable parameter for the consistency of CINE in the prevalence of such thunderstorms. The skills of the parameters are evaluated through skill score analyses. The percentage error during validation with the observation of 2010 is estimated to be 0% for the range of CINE and 3.9% for CAPE.
Highlights
Thunderstorms of pre-monsoon season (April-May) over Kolkata
The main idea of the present study is to see whether a consistent quantitative range of Convective available potential energy (CAPE) and Convective inhibition energy (CINE) can be identified for the prevalence of such thunderstorms that may aid in operational forecast
An attempt is made to identify a relationship between CAPE and CINE during the pre-monsoon thunderstorms and to see whether ranges of CAPE and CINE can be fixed so that the maximum frequency of thunderstorms remains within the stipulated ranges
Summary
Thunderstorms of pre-monsoon season (April-May) over Kolkata Precise forecast of Nor’westers continues to be a challenge for the atmospheric scientists of India. This has, doubtless, occupied the attention of the meteorologists over the last nine decades or so. All the investigations were based on the observations of surface parameters before and immediately after the occurrence of thunderstorms. Priority was given to thermodynamic parameters especially the wet bulb and wet bulb potential temperature [1]. Indian meteorologists [2] could identify well before the publication of thunderstorm project report in United States [3] that the discontinuity in temperature and moisture in the vertical plane was a favorable environment for the genesis of such thunderstorms but the large-scale flow pattern to ACS
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