The Air-Sea Interactions Regional Initiative (ASIRI) aims to understand vertical fluxes of momentum and heat across the surface layer in the Bay of Bengal. As the mesoscale and submesoscale eddies redistribute freshwater input over saline water of the bay, they influence the vertical distribution of salinity and thus impact air-sea fluxes. This study reports on numerical simulations performed to investigate processes that can lead to the observed vertical structure of stratification near the ocean surface. Processes are explored at multiple lateral scales, ranging from a few meters to tens of kilometers, to elucidate how the interplay among large-scale motion, submesoscale instabilities, and small-scale turbulent motion affects the surface layer.

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.

Arobone, E., and S. Sarkar. 2015. Effects of three-​dimensionality on instability and turbulence in a frontal zone. Journal of Fluid Mechanics 784:252–273, https://doi.org/​10.1017/jfm.2015.564.
1. Boccaletti, G., R. Ferrari, and B. Fox-Kemper. 2007. Mixed layer instabilities and restratification. Journal of Physical Oceanography 37:2,228­–2,250, https://doi.org/10.1175/JPO3101.1.
2. Burchard, H., K. Bolding, and M.R. Villarreal. 1999. GOTM–A general ocean turbulence model: Theory, applications and test cases. Technical Report EUR 18745 EN, European Commission.
3. Cantero, M.I., S. Balachandar, M.H. Garcia, and D. Block. 2008. Turbulent structures in planar gravity currents and their influence on the flow dynamics. Journal of Geophysical Research 113, C08018, https://doi.org/10.1029/2007JC004645.
4. Canuto, V.M., A. Howard, Y. Cheng, and M.S. Dubovikov. 2001. Ocean turbulence: Part I. One-point closure model—momentum and heat vertical diffusivities. Journal of Physical Oceanography 31(6):1,413–1,426, https://doi.org/10.1175/1520-0485(2001)031​<1413:OTPIOP>2.0.CO;2.
5. Capet, X., J.C. McWilliams, M.J. Molemaker, and A.F. Shchepetkin. 2008. Mesoscale to submesoscale transition in the California Current System: Part I. Flow structure, eddy flux, and observational tests. Journal of Physical Oceanography 38(1):29–43, https://doi.org/​10.1175/2007JPO3671.1.
6. Ducros, F., P. Comte, and M. Lesieur. 1996. Large-eddy simulation of transition to turbulence in a boundary layer developing spatially over a flat plate. Journal of Fluid Mechanics 326:1–36, https://doi.org/10.1017/S0022112096008221.
7. Fox-Kemper, B., R. Ferrari, and R.W. Hallberg. 2008. Parameterization of mixed layer eddies: Part I. Theory and diagnosis. Journal of Physical Oceanography 38:1,145–1,165, https://doi.org/​10.1175/2007JPO3792.1.
8. Gordon, A.L., E.L. Shroyer, A. Mahadevan, D. Sengupta, and M. Freilich. 2016. Bay of Bengal: 2013 northeast monsoon upper-ocean circulation. Oceanography 29(2):82–91, https://doi.org/10.5670/oceanog.2016.41.
9. Härtel, C., E. Meiburg, and F. Necker. 2000. Analysis and direct numerical simulation of the flow at a gravity current head: Part I. Flow topology and front speed for slip and no-slip boundaries. Journal of Fluid Mechanics 418:189–212, https://doi.org/​10.1017/S0022112000001221.
10. Hoskins, B.J., and F.P. Bretherton. 1972. Atmospheric frontogenesis models: Mathematical formulation and solution. Journal of Atmospheric Sciences 29(1):11–37, https://doi.org/10.1175/​1520-0469(1972)029<0011:AFMMFA>2.0.CO;2.
11. 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.
12. Jones, S., and A. Thorpe. 1992. The three-dimensional nature of ‘symmetric’ instability. Quarterly Journal of the Royal Meteorological Society 118:227–258, https://doi.org/10.1002/qj.49711850404.
13. Lotliker, A.A., M.M. Omand, A.J. Lucas, S.R. Laney, A. Mahadevan, and M. Ravichandran. 2016. Penetrative radiative flux in the Bay of Bengal. Oceanography 29(2):214–221, https://doi.org/10.5670/oceanog.2016.53.
14. Mahadevan, A. 2006. Modeling vertical motion at ocean fronts: Are nonhydrostatic effects relevant at submesoscales? Ocean Modelling 14:222–240, https://doi.org/10.1016/j.ocemod.2006.05.005.
15. McWilliams, J.C. 1985. Submesoscale, coherent vortices in the ocean. Reviews of Geophysics 23(2):165–182, https://doi.org/​10.1029/RG023i002p00165.
16. Mukherjee, S., A. Tandon, and A. Mahadevan. 2012. Submesoscale process studies using a new variant of second order closure. Poster presented at American Geophysical Union Fall Meeting, December 3–7, 2012, San Francisco, CA.
17. Pollard, R.T., and L.A. Regier. 1992. Vorticity and vertical circulation at an ocean front. Journal of Physical Oceanography 22(6):609–625, https://doi.org/10.1175/1520-0485(1992)022​<0609:VAVCAA>2.0.CO;2.
18. Salhi, A., and A.B. Pieri. 2014. Wave-vortex mode coupling in neutrally stable baroclinic flows. Physical Review E 90:1–15, https://doi.org/10.1103/PhysRevE.90.043003.
19. Shcherbina, A.Y., M.A. Sundermeyer, E. Kunze, E. D’Asaro, G. Badin, D. Birch, A.-M.E.G. Brunner-Suzuki, J. Calles, B.T. Kuebel Cerventes, M. Claret, and others. 2015. The LatMix summer campaign: Submesoscale stirring in the upper ocean. Bulletin of the American Meteorological Society 96:1,257–1,279, https://doi.org/10.1175/BAMS-D-14-00015.1.
20. Spall, M. 1995. Frontogenesis, subduction and cross-front exchange at upper ocean fronts. Journal of Geophysical Research 100(C2):2,543–2,557, https://doi.org/10.1029/94JC02860.
21. Tandon, A., and A. Mahadevan. 2006. An analysis of mechanisms for submesoscale vertical motion at ocean fronts. Ocean Modelling 14:241–256, https://doi.org/10.1016/j.ocemod.2006.05.006.
22. Taylor, J.R., and R. Ferrari. 2009. On the equilibrium of a symmetrically unstable front via a secondary shear instability. Journal of Fluid Mechanics 622:103–113, https://doi.org/10.1017/S0022112008005272.
23. Taylor, J.R., and R. Ferrari. 2010. Buoyancy and wind-driven convection at mixed layer density fronts. Journal of Physical Oceanography 40:1,222–1,242.
24. Thomas, L.N. 2008. Formation of intra-thermocline eddies at ocean fronts by wind-driven destruction of potential vorticity. Dynamics of Atmospheres and Oceans 45:252–273, https://doi.org/10.1016/​j.dynatmoce.2008.02.002.
25. Thomas, L.N., J.R. Taylor, R. Ferrari, and T.M. Joyce. 2013. Symmetric instability in the Gulf Stream. Deep Sea Research Part II 91:96–110, https://doi.org/​10.1016/j.dsr2.2013.02.025.
26. Vinaychandran, P.N., V.S.N. Murthy, and V. Ramesh Babu. 2002. Observations of barrier layer formation in the Bay of Bengal during summer monsoon. Journal of Geophysical Research 107(C12):1–9, https://doi.org/10.1029/2001JC000831. 
27. Weller, R.A., J.T. Farrar, J. Buckley, S. Mathew, R. Venkatesan, J. Sree Lekha, D. Chaudhuri, N. Suresh Kumar, and B. Praveen Kumar. 2016. Air-sea interaction in the Bay of Bengal. Oceanography 29(2):28–37, https://doi.org/​10.5670/oceanog.2016.36.

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