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Summer Research Fellowship Programme of India's Science Academies

Isotopic Characterisation of Rainfall Driven by Low Pressure Systems and Cyclones Over Northern Indian Ocean

Varna R Vijay

Department of Geology, School Of Earth Sciences, Central University of Karnataka

Dr. Supriyo Chakraborty

Scientist F, Indian Institute of Tropical Meteorology, Pune

Abstract

Isotopic study of rainfall is useful to understand the moisture transport processes. Temperature, rainfall amount, humidity, recycling of moisture, transport of moisture, etc., are some of the factors that control rainfall isotopic values. Low pressure systems and the associated rainfall are an integral component of the Indian monsoon. Tropical cyclone is a specialized form of the low pressure system which is typically associated with heavy to very heavy rainfall and intense wind circulation. Low pressure systems, especially cyclonic events, are believed to cause high depletions in rain water isotopic composition. The northern Indian Ocean, especially the Bay of Bengal and the Arabian Sea experience many cyclonic events during the early and later phases of a monsoon season. Isotopic characterization of those cyclone induced rainfall may provide valuable insights about the cyclonic systems. Though many such studies have been done in the Atlantic and Pacific Ocean, no significant work has so far been done in the northern Indian Ocean, viz. the Arabian Sea or Bay of Bengal. To fill this gap, we have made an attempt to collect rainwater samples from a few places in and around the Bay of Bengal that are vulnerable to cyclonic storms. Rain samples during the low pressure systems and heavy cyclonic events, such as Phailin (2013), Lehar (2013), Vardah (2016) etc., were collected mainly from Port Blair, Andaman Islands. Additionally, rain samples have also been collected from the Minicoy Island. Since the coastal regions of the North Bay of Bengal receive a major amount of monsoon rain due to low pressure systems, rain water samples have also been collected from Kolkata in the last few years. The main objective of this study is to characterize the isotopic values of rainfall induced by various kinds of low pressure systems, including the depression, deep depression and the cyclonic storms in these regions.

Keywords: Isotope, Cyclone, Kolkata, Port Blair, Minicoy Islands

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