Andhra Pradesh - Visakhapatnam   

Tropospheric heat drives Indian summer monsoon

VISAKHAPATNAM: Director of Indian Institute of Tropical Meteorology, Pune, B.N. Goswami, said that the Indian summer monsoon is more driven by the asymmetric tropospheric temperature rather than the land-ocean coordination. Delivering a lecture on fixed length of Indian summer monsoon and rainy season here , he said, “The onset and withdrawal of Indian summer monsoon may be defined when the north-south gradient of tropospheric heat source transits from negative to positive and vice-versa.”

The lecture was organised by the Department of Meteorology and Oceanography, Andhra University, and the Department of Science and Technology, New Delhi.

Professor Goswami, a recipient of Shanti Swarup Bhatnagar and Vikram Sarabhai awards, said that the June- September annual monsoon cycle has been present since over a century, and the traditional thinking suggests the cause to be the manifestation of heat source and the contrast between the land and the ocean temperatures.

“This contrast does create a low pressure, but once it starts raining the temperature on the land falls below the ocean temperature. So what exactly maintains and monitors the monsoon? It is nothing but the gradient of the tropospheric temperature,” said he.

This fact apart, he pointed out that other variables like the El Nino and the La Nina phenomena play a dominant role over the onset, withdrawal and period of monsoon over India.

“If the La Nina factor is stronger then we might expect a longer period and in case of El Nino being stronger, the monsoon period might shrink.

The north Atlantic oscillation also has a tele-connection on the tropospheric temperature gradient over India.”

Prof. Goswami said that the present monsoon was satisfactory on a larger picture and it does have a weak La Nina character.

“It is just one-month old, on a wider scale it can be predicted that the break conditions could be longer and the active period could be shorter but very vigorous.”

The Principal of College of Science and Technology, AU, P. Rajendra Prasad, and the Head of the Meteorology Department K.V.S.R. Prasad were also present.

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