Observed Variability of Temperature Inversions over the Northern Bay of Bengal with Emphasis on Recent IOD Years.
Date
2025Author
Thomas, A.P.
Suneel, V.
Karthika, P.S.
Alex, M.J.
Papa, F.
Rao, T.V.
Srinivas, G.
RamaRao, E. P.
Sudheesh, K.
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Fourteen years of monthly repeated expendable conductivity temperature depth sections across the northeastern Bay of Bengal were used to examine the interannual variability of temperature inversions during Indian Ocean dipole (IOD) years. Data averaged over three regions at the latitude band of 15 19 N along the Port Blair Kolkata shipping transect reveal occurrences of temperature inversions during November February. Notably, inversions with higher thickness (?92 m) and intensity (3.24 C) occurred at relatively shallow depths (?50 m) during the 2012 positive IOD compared to the 2016 negative IOD (?25-m thickness, 1.91 C intensity, at 86-m depth). The intensity of the inversion layer gradually weakened from Kolkata to Port Blair during the 2012 and 2019 positive IOD years and vice versa during the co-occurrence of IOD with El Ni o Southern Oscillation (ENSO) in 2015. The observed stratification was higher during 2012 and 2019 positive IOD years. Salt budget analysis revealed that the advection of freshwater plumes was the primary reason for this observed high stratification. Interestingly, on average, the inversion layer occupied 73% 86% of the barrier layer during the positive IOD years (2012 and 2019) and 40% 55% during the 2016 negative IOD (nIOD) year, from Kolkata to Port Blair. Heat budget analysis revealed that the net surface heat flux and penetrative shortwave radiation were the governing factors responsible for the observed inversion characteristics in the study region during different IOD phases. Our analysis indicates that undulations from westward-propagating Rossby waves were the driving mechanism behind the shallow and deep occurrences of inversions in our study region during the positive (2012 and 2019) and negative (2016) phases of IOD. The changes in mixed layer temperature caused by these wave processes were notably more dominant than the effect of the heat trapped in the inversion layer.
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