Summer Research Fellowship Programme of India's Science Academies

Studying the Oceanic Vertical Mixing using the KPP Boundary Layer Scheme

Siddhant Kerhalkar

Indian Institute of Technology Bhubaneswar, Arugul, Jatni 752050

Dr. Francis P.A.

Scientist-E, Head-MDG
ESSO - Indian National Centre for Ocean Information Services, "Ocean Valley", Pragathi Nagar (BO), Nizampet (SO) Hyderabad 500090


Typically, Ocean mixing is induced either due to density differences in ocean or/and due to turbulent motions. Boundary Layer Depth is an indication of how deep a boundary layer is i.e. how deep the turbulent eddies can penetrate. Hence to study the vertical mixing in Boundary layer as well as in the interior of the Ocean, diffusivity is a very important parameter. Diffusivity in the boundary layer is a function of shape function and is difficult to be found directly, whereas the diffusivities in the Interior Ocean are relatively easy to find. Hence using the KPP Boundary Layer Scheme, we can try to match the diffusivities at the Boundary layer depth as to obtain the shape function and thus obtain the diffusivity in the Boundary Layer. Vertical Mixing in ocean interior is regarded as the superposition of three processes: resolved vertical shear, internal wave breaking and double diffusion. The parameterization for shear induced mixing is done in a satisfactory way (according to Large et al. 1994). The parameterization for internal wave breaking is difficult due to its complexity and is untouched. The mixing due to double diffusion can happen when the vertical gradient of either salinity (known as Salt Fingering) or temperature (diffusive convection) is unstable in its contribution to density. The parameterization of this involves a lot of constant values which might be due to the geographical locations involved in this test. Hence this might be a source of error while implementing this scheme in the model at other locations and should be researched further to avoid errors. Depending on the success of matching, the shape function can be found out as a function of depth and thus the diffusivity can be found out in Boundary Layer and thus mixing in the Ocean can be studied effectively.

Keywords: Diffusivity, Shape Function, Double Diffusion, Mixed Layer, Boundary Layer, Parameterization

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