The sharp depletion of attenuation of 22.235 GHz signal before the onset of Nor'wester over Kolkata, India is observed and possible explanation of such type of variation is presented. It is concluded that this may be taken as one possible method of forecasting severe thunderstorm associated with Nor'wester. Physical explanations based on the formation and dissipation mechanisms of thunderstorm are also presented. © 2010 IACS.

SUBRATA MIDYA

Atmospheric Science

H SARKAR

S S DEY

A MAITRA

M GHOSH

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Indian Journal of Physics

Thunderstorm, associated with strong convective activity in the tropics, is one of the most prominent weather phenomena in the atmosphere. A critical analysis is done on the nature of variation of the thunderstorm frequencies over an urban metropolitan location Kolkata (22°32'N, 88°20'E), India with the pre-monsoon and monsoon rainfall amounts during the period 1997-2008. The occurrences of severe thunderstorms are decreasing during the last decade, although the number of ordinary thunderstorms occurring in this period has an increasing trend. A decrease in Convective Available Potential Energy (CAPE), Vertical Wind Shear (VWSH), Deep Layer Shear (0-6. km AGL) and an increase in Lifted Index (LI) may be an indicator for the suppression of the severity of thunderstorms over the urban location. There is also a decreasing trend for the pre-monsoon rainfall and an increasing trend in the monsoon rainfall amounts over the region. A further study indicated a significant positive correlation for all the types of thunderstorm (severe, ordinary and total) events with the pre-monsoon rainfall amount which are mainly associated with the vigorous convective phenomenon. On the other hand, a significant anti-correlation is observed between the severe thunderstorm frequencies with the monsoon rainfall amount for the same period. The decrease in the severity of the thunderstorm events is accompanied by an increase of pre-monsoon cloud Liquid Water Content (LWC) with Integrated Water Vapor (IWV). Hence, there is an expected strong association of the thunderstorm frequency with the pre-monsoon and monsoon rainfall amounts at this tropical location. Possible explanations are presented. © 2013 Elsevier B.V.

Atmospheric Research

Association of thunderstorm frequency with rainfall occurrences over an Indian urban metropolis

The paper presents the nature of variation of refractive index of atmospheric medium before the onset of squall over kolkata (22 34′N 88 22′E), India. The variation of the refractive index with surface temperature and relative humidity during squall is also presented. It is concluded that sharp decrease of the refractivity may be taken as a possible method of forecasting squall. This kind of study is very much helpful from the standpoint of aviation hazards and communication. Possible explanation for the observed results is also presented. © 2013 Indian Association for the Cultivation of Science.

Study of atmospheric refractivity prior to squall onset and its strong association with surface temperature and relative humidity over Kolkata (22 34â€²N, 88 22â€²E)

The paper presents the nature of the variation of refractive index of atmospheric medium with time and altitude before, during and after the onset of thunderstorms over Gangetic West Bengal during the pre-monsoon period. A critical analysis shows that sharp depletion of the refractive index takes place before the onset of Nor'westers and possible explanations are also offered for the said occurrence. © 2011 Springer-Verlag.

Journal	Indian Journal of Physics
Publisher	INDIAN ASSOC CULTIVATION SCIENCE
ISSN	0973-1458
Open Access	No