The southwest monsoon landed in Kerala on Thursday, delayed by a week against the annual date of June 1. According to studies, climate change is already affecting the seasonality and characteristics of summer monsoon, especially when the formation of tropical cyclones is increasing around the time of monsoon onset.
According to Dr S Abhilash, Director of CUSAT Advanced Centre for Atmospheric Radar Research, there have been seven cyclones in the Arabian Sea in the last 10 years.
From Nanuak in 2014, there was Ashobha in 2015, Sagar and Meknu in 2018, Vayu in 2019, Nisarga in 2020, Takte in 2021 and Biparjoy in 2023.
During recent decades, the Arabian Sea witnessed frequent occurrences of cyclones as part of the onset phase of the
Cyclone formation is the result of warm ocean water with surface temperatures above 26.5 degrees Celsius. This provides the energy and moisture required for cyclone development. Warm and moist air in the lower atmosphere and colder air in the upper one helps development of massive clouds and thunderstorms necessary for cyclones. Besides, low vertical wind shear prevents its circulation disruption.
Revised monsoon onset dates by the Indian Meteorological Department are the result of concurrent occurrence of
cyclones during the onset phase which can influence the further establishment of monsoon over the entire Indian subcontinent, says a recent study by CUSAT atmosphere scientists PK Babu, S Abhilash and others. Monsoon propagates faster along the west coast.
Why does the sea get hot?
During the summer solstice around June 21, the Northern Hemisphere of the Earth is tilted towards the Sun, resulting in longer daylight hours and better direct sunlight. This leads to higher insolation, or the amount of solar radiation received, during the summer months. The increased solar radiation causes greater heating of the Arabian Sea's surface is the reason for the sea to remain warm even during the monsoon period, resulting in cyclones at frequent intervals as observed of late. It is converse during the winter solstice around December 21.
It is these seasonal variations in solar radiation and insolation during the two solstices that result in overall fluctuation of sea surface temperature (SST) in the Arabian Sea throughout the year.
During the Southwest Monsoon, the winds blow from the southwest, bringing warm and moist air over the Arabian Sea, raising the SST.
PRE-MONSOON CYCLONES IN ARABIAN SEA
2018 Sagar, Meknu