Indo-Norwegian cooperative studies on the cold pool in the Bay of Bengal during the Indian summer monsoon

Scientists at the Nansens Centers in Cochin, India and Bergen have published new results in Atmospheric and Oceanic Science Letters (AOSL) on the appearance of surface cold water pool of the Bay of Bengal associated with the break phase of the Indian summer monsoon. The study was led by Dr. Mary Swapna George, who defended her Doctoral Modelling and observations of upwelling along the southwest coast of India and its intrusion into the Bay of Bengal, during summer monsoon at University of Bergen in January 2015. The results presented in the paper The cold pool of the Bay of Bengal and its association with the break phase of the Indian summer monsoon are based on of ocean and meteorological data, including sea surface temperature, ocean currents, rainfall and surface wind data in order to investigate how enhanced cooling in the cold pool region during monsoon spells is associated with the strong westerly wind stress there during the break spells of the monsoon.

The strong monsoonal winds over the Indian Ocean play a major role in driving the surface currents of the region, thus influencing the sea surface temperature (SST) in the Indian Ocean. During the summer monsoon season, strong coastal upwelling occurs along the southwest coast of India and at the southern tip of India, which cools the surface temperature of the waters around these regions. The summer monsoon current carries the upwelled cold waters into the Bay of Bengal and forms the ‘cold pool of the Bay of Bengal’, with its core south of Sri Lanka and over the south- central Bay of Bengal. The present study focuses on the intrusion of these cold waters into the south of the Bay of Bengal, its interannual variability, and its association with the surface wind during the break phase of the summer monsoon, when strong westerly surface winds flow south of 10°N. The authors have in the paper suggested that the enhanced cooling in the cold pool region during monsoon spells is associated with the strong westerly wind stress there during the break spells of the monsoon. Composites of sea surface temperature (SST units: °C) from Tropical Meteorological Institute (TMI), for the seven break periods and three active periods of summer monsoon during 2002–2009. The mean differences of SST (units: °C) between the two phases (break minus active) are also plotted.Composites of sea surface temperature (SST units: °C) from Tropical Meteorological Institute (TMI), for the seven break periods and three active periods of summer monsoon during 2002–2009. The mean differences of SST (units: °C) between the two phases (break minus active) are also plotted.They observe significant differences between the SST patterns during break and active periods of the summer monsoon. Intense cooling in the cold pool region is found during break periods. Also observed is a southward extension of these cold waters towards the equator. Whereas, during active periods, the enhanced cooling is absent in the cold pool region. The surface winds show a shift towards the south of India during break periods, while in the active monsoon period the axis of the wind is over mainland India. Seven cases of long break monsoon spells that occurred during the nine years from 2001 to 2009 are analysed, and the results confirm their hypothesis.

The current study started during Dr. Mary Swapna Georges doctoral studies conducted at the Nansen Center in Bergen and finalized later at the Nansen Center in Cochin. The research has been supported by a donation from Trond Mohn, c/o Frank Mohn AS, as well as grants from the Nansen Scientific Society and EU-FP7 [project number 295092] INDO-MARECLIM.

 

Citation: Mary Swapna GEORGE, Porathur Vareed JOSPEH, Kochuparampil Ajith JOSPEH, Laurent BERTINO & Ola Mathias JOHANNESSEN (2017): The cold pool of the Bay of Bengal and its association with the break phase of the Indian summer monsoon, Atmospheric and Oceanic Science Letters. http://dx.doi.org/10.1080/16742834.2017.1294017 

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