Continuous time-series measurements of near surface meteorological and ocean variables obtained from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) moorings at 15°N, 90°E; 12°N, 90°E; and 8°N, 90°E and an Ocean Moored buoy Network for Northern Indian Ocean (OMNI) mooring at 18°N, 90°E are used to improve understanding of air-sea interaction processes and mixed layer (ML) temperature variability in the Bay of Bengal (BoB) at seasonal time scales. Consistent with earlier studies, this analysis reveals that net surface heat flux primarily controls the ML heat balance. The penetrative component of shortwave radiation plays a crucial role in the ML heat budget in the BoB, especially during the spring warming phase when the ML is thin. During winter and summer, vertical processes contribute significantly to the ML heat budget. During winter, the presence of a strong barrier layer and a temperature inversion (warmer water below the ML) leads to warming of the ML by entrainment of warm subsurface water into the ML. During summer, the barrier layer is relatively weak, and the ML is warmer than the underlying water (i.e., no temperature inversion); hence, the entrainment cools the mixed layer. The contribution of horizontal advection to the ML heat budget is greatest during winter when it serves to warm the upper ocean. In general, the residual term in the ML heat budget equation is quite large during the ML cooling phase compared to the warming phase when the contribution from vertical heat flux is small. 

Thangaprakash, V.P., M.S. Girishkumar, K. Suprit, N. Suresh Kumar, D. Chaudhuri, K. Dinesh, A. Kumar, S. Shivaprasad, M. Ravichandran, J.T. Farrar, R. Sundar, and R.A. Weller. 2016. What controls seasonal evolution of sea surface temperature in the Bay of Bengal? Mixed layer heat budget analysis using moored buoy observations along 90°E. Oceanography 29(2):202–213, https://doi.org/10.5670/oceanog.2016.52.

Bhat, G.S., and H.J.S. Fernando. 2016. Remotely driven anomalous sea-air heat flux over the north Indian Ocean during the summer monsoon season. Oceanography 29(2):232–241, https://doi.org/10.5670/oceanog.2016.55.

Bhat, G.S., and R. Narasimha. 2007. Indian summer monsoon experiments. Current Science 93(2):153–164.

Boyer Montégut, C., J. Vialard, S.S.C. Shenoi, D. Shankar, F. Durand, C. Ethé, and G. Madec. 2007. Simulated seasonal and interannual variability of mixed layer heat budget in the northern Indian Ocean. Journal of Climate 20:3,249–3,268, https://doi.org/10.1175/JCLI4148.1.

Chowdary, J.S., A. Parekh, S. Ojha, and C. Gnanaseelan. 2015. Role of upper ocean processes in the seasonal SST evolution over tropical Indian Ocean in climate forecasting system. Climate Dynamics 45:2,387–2,405, https://doi.org/10.1007/s00382-015-2478-4.

Dickey, T.D., D.V. Manov, R.A. Weller, and D.A. Siegel. 1994. Determination of longwave heat flux at the air-sea interface using measurements from buoy platforms. Journal of Atmospheric and Oceanic Technology 11(4):1,057–1,078, https://doi.org/10.1175/​1520-0426(1994)011<1057:DOLHFA>2.0.CO;2.

Du, Y., T. Qu, G. Meyers, Y. Masumoto, and H. Sasaki. 2005. Seasonal heat budget in the mixed layer of the southeastern tropical Indian Ocean in a high-resolution ocean general circulation model. Journal of Geophysical Research 110, C04012, https://doi.org/10.1029/2004JC002845.

Fairall, C.W., E.F. Bradley, J.E. Hare, A.A. Grachev, and J.B. Edson. 2003. Bulk parameterization of air-sea fluxes: Updates and verification for the COARE algorithm. Journal of Climate 16:571–591, https://doi.org/10.1175/1520-0442(2003)016​<0571:BPOASF>2.0.CO;2. 

Gentemann, C., C.J. Donlon, A. Stuart-Menteth, and F.J. Wentz. 2003. Diurnal signals in satellite sea surface temperature measurements. Geophysical Research Letters 30(3):1,140–1,143, https://doi.org/​10.1029/2002GL016291.

Girishkumar, M.S., M. Ravichandran, and M.J. McPhaden. 2013. Temperature inversions and their influence on the mixed layer heat budget during the winters of 2006–2007 and 2007–2008 in the Bay of Bengal. Journal of Geophysical Research 118:2,426–2,437, https://doi.org/​10.1002/jgrc.20192.

Girishkumar, M.S., M. Ravichandran, M.J. McPhaden, and R.R. Rao. 2011. Intraseasonal variability in barrier layer thickness in the south central BoB. Journal of Geophysical Research 116, C03009, https://doi.org/10.1029/2010JC006657.

Kara, A.B., P.A. Rochford, and H.E. Hurlbutt. 2000. Mixed layer depth variability and barrier layer formation over the North Pacific Ocean. Journal of Geophysical Research 105(C7):16,783–16,801, https://doi.org/10.1029/2000JC900071.

Lukas, R., and E. Lindstrom. 1991. The mixed layer of the western equatorial Pacific Ocean. Journal of Geophysical Research 96:3,343–3,357, https://doi.org/10.1029/90JC01951.

McPhaden, M.J. 1982. Variability in the central equatorial Indian Ocean: Part II. Oceanic heat and turbulent energy balance. Journal of Marine Research 40:403–419.

McPhaden, M.J., G. Meyers, K. Ando, Y. Masumoto, V.S.N. Murty, M. Ravichandran, F. Syamsudin, J. Vialard, L. Yu, and W. Yu. 2009. RAMA, The Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction: A new moored buoy array in the historically data-sparse Indian Ocean provides measurements to advance monsoon research and forecasting. Bulletin of the American Meteorological Society 90:459–480, https://doi.org/10.1175/2008BAMS2608.1.

Morel, A. 1988. Optical modeling of the upper ocean in relation to its biogenous matter content (case I waters). Journal of Geophysical Research 93:1,652–1,665, https://doi.org/10.1029/JC093iC09p10749.

Nagura, M., T. Terao, and M. Hashizume. 2015. The role of temperature inversions in the generation of seasonal and interannual SST variability in the far northern Bay of Bengal. Journal of Climate 28:3,671–3,693, https://doi.org/10.1175/JCLI-D-14-00553.1.

Neethu, C., M. Ravichandran, R.R. Rao, and S.S.C. Shenoi. 2012. An anomalous cooling event observed in the Bay of Bengal during June 2009. Ocean Dynamics 62(5):671–681, https://doi.org/10.1007/s10236-012-0525-9.

Palmer, T.N., and D.A. Mansfield. 1984. Response of two atmospheric general circulation models to sea-surface temperature anomalies in the tropical east and west Pacific. Nature 310:483–488, https://doi.org/10.1038/310483a0.

Parampil, S.R., A. Gera, M. Ravichandran, and D. Sengupta. 2010. Intraseasonal response of mixed layer temperature and salinity in the Bay of Bengal to heat and freshwater flux. Journal of Geophysical Research 115, C05002, https://doi.org/10.1029/2009JC005790.

Prasad, T.G. 2004. A comparison of mixed-layer dynamics between the Arabian Sea and Bay of Bengal: One-dimensional model results. Journal of Geophysical Research 109, C03035, https://doi.org/10.1029/2003JC002000.

Praveen Kumar, B., J. Vialard, M. Lengaigne, V.S.N. Murty, and M.J. McPhaden. 2012. TropFlux: Air-sea fluxes for the global tropical oceans–description and evaluation. Climate Dynamics 38:1,521–1,543, https://doi.org/10.1007/s00382-011-1115-0.

Rao, R.R., and R. Sivakumar. 2000. Seasonal variability of near-surface thermal structure and heat budget of the mixed layer of the tropical Indian Ocean from a new global ocean temperature climatology. Journal of Geophysical Research 105(C1):995–1,016, https://doi.org/​10.1029/1999JC900220.

Rao, R.R., and R. Sivakumar. 2003. Seasonal variability of sea surface salinity and salt budget of the mixed layer of the north Indian Ocean. Journal of Geophysical Research 108(C1), 3009, https://doi.org/10.1029/2001JC000907. 

Sengupta, D., B.R. Goddalehundi, and D.S. Anitha. 2007. Cyclone-induced mixing does not cool SST in the post-monsoon North Bay of Bengal. Atmospheric Science Letters 9:1–6, https://doi.org/10.1002/asl.162.

Sengupta, D., B.N. Goswami, and R. Senan. 2001. Coherent intraseasonal oscillations of ocean and atmosphere during the Asian summer monsoon. Geophysical Research Letters 28(21):4127–4130, https://doi.org/10.1029/2001GL013587.

Sengupta, D., and M. Ravichandran. 2001. Oscillations in the Bay of Bengal sea surface temperature during the 1998 summer monsoon. Geophysical Research Letters 28:2,033–2,036, https://doi.org/​10.1029/2000GL012548.

Sengupta, D., P.K. Ray, and G.S. Bhat. 2002. Spring warming of the eastern Arabian Sea and Bay of Bengal from buoy data. Geophysical Research Letters 29(15), https://doi.org/​10.1029/2002GL015340.

Sharmila, S., P.A. Pillai, S. Joseph, M. Roxy, R.P.M. Krishna, R. Chattopadhyay, S. Abhilash, A.K. Sahai, and B.N. Goswami. 2013. Role of ocean–atmosphere interaction on northward propagation of Indian summer monsoon intra-seasonal oscillations (MISO). Climate Dynamics 41(5):1,651–1,669, https://doi.org/10.1007/s00382-013-1854-1.

Shenoi, S.S.C., D. Shankar, and S.R. Shetye. 2002. Differences in heat budgets of the near-surface Arabian Sea and Bay of Bengal: Implications for the summer monsoon. Journal of Geophysical Research 107(C6), https://doi.org/​10.1029/2000JC000679.

Shetye, S.R., A.D. Gouveia, D. Shankar, S.S.C. Shenoi, P. Vinayachandran, N. Sundar, G.S. Michael, and G. Namboodiri. 1996. Hydrography and circulation in the western Bay of Bengal during the northeast monsoon. Journal of Geophysical Research 101(6):14,011–14,025, https://doi.org/​10.1029/95JC03307.

Shroyer, E.L., D.L. Rudnick, J.T. Farrar, B. Lim, S.K. Venayagamoorthy, L.C. St. Laurent, A. Garanaik, and J.N. Moum. 2016. Modification of upper-ocean temperature structure by subsurface mixing in the presence of strong salinity stratification. Oceanography 29(2):62–71, https://doi.org/10.5670/oceanog.2016.39.

Sprintall, J., and M. Tomczak. 1992. Evidence of the barrier layer in the surface layer of the tropics. Journal of Geophysical Research 97:7,305–7,316, https://doi.org/10.1029/92JC00407.

Thadathil, P., V.V. Gopalakrishna, P.M. Muraleedharan, G.V. Reddy, N. Araligidad, and S. Shenoy. 2002. Surface layer temperature inversion in the Bay of Bengal. Deep Sea Research Part I (49):1,801–1,818, https://doi.org/10.1016/S0967-0637(02)00044-4.

Thadathil, P., P.M. Muraleedharan, R.R. Rao, Y.K. Somayajulu, G.V. Reddy, and C. Revichandran. 2007. Observed seasonal variability of barrier layer in the Bay of Bengal. Journal of Geophysical Research 112, C02009, https://doi.org/​10.1029/2006JC003651.

Venkatesan, R., V.R. Shamji, G. Latha, S. Mathew, R.R. Rao, A. Muthiah, and M.A. Atmanand. 2013. In situ ocean subsurface time-series measurements from OMNI buoy network in the Bay of Bengal. Current Science 104:1,166–1,177.

Vialard, J., G.R. Foltz, M.J. McPhaden, J.P. Duvel, and C. de Boyer Montégut. 2008. Strong Indian Ocean sea surface temperature signals associated with the Madden-Julian Oscillation in late 2007 and early 2008. Geophysical Research Letters 35, L19608, https://doi.org/10.1029/2008GL035238. 

Warner, S.J., J. Becherer, K. Pujiana, E.L. Shroyer, M. Ravichandran, V.P. Thangaprakash, and J.N. Moum. 2016. Monsoon mixing cycles in the Bay of Bengal: A year-long subsurface mixing record. Oceanography 29(2):158–169, https://doi.org/10.5670/oceanog.2016.48.

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.