The India Meteorological Department (IMD) has recently predicted that Cyclone Asani is set to escalate into a ‘severe cyclone’ over the Southeast regions of Bay of Bengal. This cyclone, named Asani (meaning ‘wrath’ in Sinhalese), was given its moniker by Sri Lanka.
Past Cyclones: A Glimpse Back
Notably, in 2020-21, India was hit by several powerful cyclones such as Tauktae, Yaas, Nisarga, and Amphan. To familiarize oneself with the storm patterns in India, it’s essential to understand that India witnesses a bi-annual cyclone season, spanning from March to May and October to December. However, rare instances have recorded cyclones even in June and September. For instance, Cyclone Gulab, which landed over the east coast in September, became the third cyclone of the 21st century to do so, following tropical cyclone Daye in 2018 and Pyarr in 2005.
Cyclone Occurrence & Intensity: Unveiling Patterns
Typically, tropical cyclones in the North Indian Ocean region, encompassing the Bay of Bengal and the Arabian Sea, usually develop during the pre-monsoon (April to June) and post-monsoon (October to December) phases. May-June and October-November are particularly known for spawning cyclones of serious intensity affecting the Indian coasts.
Cyclone Classification: Understanding the Basics
It’s crucial to comprehend how cyclones are classified by the IMD. This classification is primarily based on the Maximum Sustained Surface Wind Speed (MSW) they generate. Here, the categories range from severe (MSW of 48-63 knots), to very severe (MSW of 64-89 knots), extremely severe (MSW of 90-119 knots), and finally, the super cyclonic storm (MSW of 120 knots or more). Here, one knot is equal to 1.8 kmph.
Unraveling Tropical Cyclones
A tropical cyclone, essentially an intense circular storm originating over warm tropical oceans, is characterized by low atmospheric pressure, high winds, and heavy rain. These storms are known as hurricanes in the North Atlantic and the eastern Pacific, typhoons in Southeast Asia and China, tropical cyclones in the southwest Pacific and the Indian Ocean region, and Willy-willies in north-western Australia. The rotation of these storms varies based on hemisphere – counterclockwise in the northern and clockwise in the southern.
Formation and Intensification Conditions of Tropical Storms
Certain factors prove conducive for the formation and intensification of tropical storms. These include a large sea surface with a temperature higher than 27° C, presence of the Coriolis force, small deviations in the vertical wind speed, a pre-existing weak low-pressure area or low-level-cyclonic circulation, and upper divergence above the sea level system.
Past UPSC Civil Services Examination Questions
In the previous year’s UPSC Civil Services Examination, questions were asked pertaining to cyclones and related topics. One such query was whether jet streams occur only in the Northern Hemisphere and if only some cyclones develop an eye. Another question probed if the temperature inside the eye of a cyclone is nearly 10ºC less than its surroundings. Correct answers revealed that Jet Streams extend from 20° latitude to the poles in both hemispheres, and not all cyclones develop an eye. Furthermore, it was clarified that the temperature inside a cyclone’s eye is warmer, and not cooler, than its surroundings.
