Oceanography The Official Magazine of
The Oceanography Society
Volume 29 Issue 02

View Issue TOC
Volume 29, No. 2
Pages 170 - 179

Ocean Turbulence and Mixing Around Sri Lanka and in Adjacent Waters of the Northern Bay of Bengal

S.U.P. JinadasaIossif Lozovatsky Jesús Planella-MoratóJonathan D. NashJennifer A. MacKinnonAndrew J. Lucas Hemantha W. Wijesekera Harinda J.S. Fernando
Article Abstract

As a part of the US Air-Sea Interactions Regional Initiative, the first extensive set of turbulent kinetic energy dissipation rate (ε) measurements from microstructure profilers were obtained in the Bay of Bengal (BoB) and around Sri Lanka during 2013–2015. The observations span almost 1,200 km meridionally, and capture the dynamics associated with a variety of mesoscale and submesoscale features. High freshwater input in the northern part of the basin leads to regions of intense near-surface stratification, which become weaker moving south. The thin layers trap mechanical energy input from the atmosphere, often confining turbulence to the surface boundary layer. These thin layers can form shallow fronts, which at times resemble turbulent gravity currents (Sarkar et al., 2016, in this issue), and are associated with high levels of mixing. Away from the local frontal zones, turbulence in the surface low-salinity layer appears to be decoupled from the underlying pycnocline, where turbulence occurs only in rare and sporadic breaking events. A striking feature common to all of the data acquired is a dearth of turbulent mixing at depth, a condition that appears to be pervasive throughout the basin except during the passage of tropical storms. It is likely that the strong near-surface stratification effectively isolates the deeper water column from mechanical penetration of atmospheric energy.

Citation

Jinadasa, S.U.P., I. Lozovatsky, J. Planella-Morató, J.D. Nash, J.A. MacKinnon, A.J. Lucas, H.W. Wijesekera, and H.J.S. Fernando. 2016. Ocean turbulence and mixing around Sri Lanka and in adjacent waters of the northern Bay of Bengal. Oceanography 29(2):170–179, https://doi.org/10.5670/oceanog.2016.49.

References

Akhil, V.P., F. Durand, M. Lengaigne, J. Vialard, M.G. Keerthi, V.V. Gopalakrishna, C. Deltel, F. Papa, and C. de Boyer Montégut. 2014. A modeling study of the processes of surface salinity seasonal cycle in the Bay of Bengal. Journal of Geophysical Research 119(6):3,926–3,947, https://doi.org/​10.1002/2013JC009632

de Vos, A., C.B. Pattiaratchi, and E.M.S. Wijeratne. 2014. Surface circulation and upwelling patterns around Sri Lanka. Biogeosciences 11:5,909–5,930, https://doi.org/10.5194/bg-11-5909-2014.

Gregg, M.C. 1999. Uncertainties and limitations in measuring ε and χT. Journal of Atmospheric and Oceanic Technology 16:1483–1490, https://doi.org/10.1175/1520-0426(1999)016​<1483:UALIMA>2.0.CO;2.

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

Jensen, T.G. 2001. Arabian Sea and Bay of Bengal exchange of salt and tracers in an ocean model. Geophysical Research Letters 28(20):3,967–3,970, https://doi.org/10.1029/2001GL013422.

Jensen, T.G. 2003. Cross-equatorial pathways of salt and tracers from the northern Indian Ocean: Modelling results. Deep Sea Research Part II 50(12):2,111–2,127, https://doi.org/10.1016/S0967-0645(03)00048-1.

Kunze, E., E. Firing, J.M. Hummon, T.K. Chereskin, and A.M. Thurnherr. 2006. Global abyssal mixing inferred from lowered ADCP shear and CTD strain profiles. Journal of Physical Oceanography 36(8):1,553–1,576, https://doi.org/10.1175/JPO2926.1.

Lee, C.M., S.U.P. Jinadasa, A. Anutaliya, L.R. Centurioni, H.J.S. Fernando, V. Hormann, M. Lankhorst, L. Rainville, U. Send, and H.W. Wijesekera. 2016. Collaborative observations of boundary currents, water mass variability, and monsoon response in the southern Bay of Bengal. Oceanography 29(2):102–111, https://doi.org/10.5670/oceanog.2016.43.

Liu, Z., H. Wei, I.D. Lozovatsky, and H.J.S. Fernando. 2009. Late summer stratification and turbulence in the Yellow Sea. Journal of Marine Systems 77:459–472, https://doi.org/10.1016/​j.jmarsys.2008.11.001.

Lozovatsky, I., J.-H. Lee, H.J.S. Fernando, S.K. Kang, and S.U.P. Jinadasa. 2015. Turbulence in the East China Sea: The summertime stratification. Journal of Geophysical Research 120:1,856–1,871, https://doi.org/10.1002/2014JC010596.

Lozovatsky, I., Z. Liu, H.J.S. Fernando, J. Armengol, and E. Roget. 2012. Shallow water tidal currents in close proximity to the seafloor and boundary-​induced turbulence. Ocean Dynamics 62:177–201, https://doi.org/10.1007/s10236-011-0495-3.

Lucas, A.J., E.L. Shroyer, H.W. Wijesekera, H.J.S. Fernando, E. D’Asaro, M. Ravichandran, S.U.P. Jinadasa, D. Sengupta, J.A. MacKinnon, J.D. Nash, and others. 2014. Mixing to monsoons: Air-sea interactions in the Bay of Bengal. Eos, Transactions American Geophysical Union 95:269-276, https://doi.org/​10.1002/​2014EO300001.

MacKinnon, J.A., J.D. Nash, M.H. Alford, A.J. Lucas, J.B. Mickett, E.L. Shroyer, A.F. Waterhouse, A. Tandon, D. Sengupta, A. Mahadevan, and others. 2016. A tale of two spicy seas. Oceanography 29(2):50–61, https://doi.org/​10.5670/oceanog.2016.38.

Mukherjee, A., D. Shankar, V. Fernando, P. Amol, S.G. Aparna, R. Fernandes, G.S. Michael, S.T. Khalap, N.P. Satelkar, Y. Agarvadekar, and others. 2014. Observed seasonal and intraseasonal variability of the East India Coastal Current on the continental slope. Journal of Earth System Science 123(6):1,197–1,232, https://doi.org/10.1007/s12040-014-0471-7.

Phillips, O.M., J.H. Shyu, and H. Salmun. 1986. An experiment on boundary mixing: Mean circulation and transport rates. Journal of Fluid Mechanics 173:473–499, https://doi.org/10.1017/S0022112086001234.

Pollard, R.T., P.B. Rhines, and R. Thompson. 1972. The deepening of the wind-mixed layer. Geophysical Fluid Dynamics 4(1):381–404, https://doi.org/​10.1080/03091927208236105.

Roget, E., I. Lozovatsky, X. Sanchez, and M. Figueroa. 2006. Microstructure measurements in natural waters: Methodology and applications. Progress in Oceanography 70:123–148, https://doi.org/​10.1016/j.pocean.2006.07.003

Sarkar, S., H.T. Pham, S. Ramachandran, J.D. Nash, A. Tandon, J. Buckley, A.A. Lotliker, and M.M. Omand. 2016. The interplay between submesoscale instabilities and turbulence in the surface layer of the Bay of Bengal. Oceanography 29(2):146–157, https://doi.org/10.5670/oceanog.2016.47.

Sengupta, D., G.N. Bharath Raj, M. Ravichandran, J. Sree Lekha, and F. Papa. 2016. Near-surface salinity and stratification in the north Bay of Bengal from moored observations. Geophysical Research Letters 43(8):1–9, https://doi.org/​10.1002/2016GL068339.

Shetye, S.R. 1993. The movement and implications of the Ganges-Brahmaputra runoff on entering the Bay of Bengal. Current Science 64(1):32–38. 

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

Strang, E.J., and H.J.S. Fernando. 2001. Entrainment and mixing in stratified shear flows. Journal of Fluid Mechanics 428:349–386, https://doi.org/10.1017/S0022112000002706.

Turner, J.S. 1973. Buoyancy Effects in Fluids. Cambridge University Press, 368 p.

Vinayachandran, P.N., D. Shankar, S. Vernekar, K.K. Sandeep, P. Amol, C.P. Neema, and A. Chatterjee. 2013. A summer monsoon pump to keep the Bay of Bengal salty. Geophysical Research Letters 40:1,777–1,782, https://doi.org/​10.1002/grl.50274.

Whalen, C.B., L.D. Talley, and J.A. MacKinnon. 2012. Spatial and temporal variability of global ocean mixing inferred from Argo profiles. Geophysical Research Letters 39(18), L18612, https://doi.org/10.1029/2012GL053196.

Wijesekera, H.W., T.G. Jensen, E. Jarosz, W.J. Teague, E.J. Metzger, D.W. Wang, S.U.P. Jinadasa, K. Arulananthan, L. Centurioni, and H.J.S. Fernando. 2015. Southern Bay of Bengal currents and salinity intrusions during a fall monsoon transition. Journal of Geophysical Research: Oceans 120(10):6,897–6,913, https://doi.org/​10.1002/2015jc010744.

Wijesekera, H.W., E. Shroyer, A. Tandon, M. Ravichandran, D. Sengupta, S.U.P. Jinadasa, H.J.S. Fernando, N. Agrawal, K. Arulanathan, G.S. Bhat, and others. In press. ASIRI: An ocean-​atmosphere initiative for Bay of Bengal. Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-14-00197.1.

Zilitinkevich, S., I. Esau, and A. Baklanov. 2007. Further comments on the equilibrium height of neutral and stable planetary boundary layers. Quarterly Journal of the Royal Meteorological Society 133:265–271, https://doi.org/10.1002/qj.27.