Expert sceptical over the advance of the monsoon over the Indian mainland
Cyclone Amphan has created conditions that are favourable for the “advance of the southwest monsoon over the south Bay of Bengal, Andaman Sea and Andaman and Nicobar Islands around May 16,” the India Meteorological Department (IMD) said on May 14, 2020.
However, IMD did not say anything about the advance of the monsoon over the Indian mainland in its press statement.
Amphan is currently brewing in the Bay of Bengal and is most likely going to form on the evening of May 16, according to the IMD.
“The low-pressure trough that eventually anchors itself to the southern tip of India and initiates the monsoon onset, marches in the northwestward direction from the northwest tropical Pacific into the South China Sea and then to the Bay of Bengal,” Raghu Murtugudde, a climate scientist at the University of Maryland in the United States, told Down To Earth.
When Amphan forms and grows in the southeastern parts of the Bay of Bengal and moves in the north eastern direction, it will facilitate the north western movement of the monsoon low pressure trough.
The cyclone will move in a counter-clockwise direction, pulling in the winds from around itself to grow in intensity. While doing this, the cyclone will also pull the monsoon winds towards the Andaman Sea, commencing the rainfall season in the region.
An image showing higher than normal sea temperatures currently
Last year too there was an extremely severe cyclone in the Bay of Bengal, Cyclone Fani in May, a month before the onset of the south west monsoon season, though there is no evidence of its impact on the onset of the south west monsoon season last year.
Then just after the onset of the monsoon season there was slow progress of the monsoon winds. This was brought about by the development, propagation and dissipation of very severe Cyclone Vayu in the Arabian Sea over nine days from June 9 to June 17.
The winds of the cyclone disrupted the regular trade winds in the region, which are the carriers of monsoon. This kept the monsoon arrested in Kerala, Tamil Nadu and Karnataka till June 21.
Once the monsoon winds resumed there circulation the rain came in torrents and flooded large parts of the country from early July to mid October.
The monsoon winds have become weaker in the last few decades leading to decrease in overall rainfall on the Indian sub-continent, according to a research paper published by scientists from Harvard University, Peking University and Chinese Meteorological Administration in the journal Science Advances in December 2018.
Significant warming in the Indian Ocean has decreased the temperature difference between the land and the sea which is the main trigger for the flow of monsoon winds, according to the study. This time around the land is much cooler than in the last many years which could have a possible impact on the onset of the south west monsoon season.
An image showing cooler-than-normal land temperatures
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