Modelling of Arabian Sea processes and investigation of Turbulent Kinetic Energy using Modular Ocean Model

Arabian sea (AS), a north Indian Ocean basin plays a significant role in the transfer of energy and moisture flux during the Indian summer monsoon. It is crucial to understand mixing in AS that affects ocean properties and subsequently the interaction between ocean and atmosphere. A huge amount of energy from the atmosphere in the form of winds is enforced to the ocean surface of Arabian Sea in summer monsoon which develops various large scale features such as Somali current, the great whirl, Socotra eddy and helps in churning the ocean layers. Thus in this study, standalone Ocean circulation model, Modular Ocean Model (MOM5) is used to study the dynamics and energetics of Arabian Sea in regional ocean domain. Regional AS with domain extent between 38 to 79⁰ E in longitude and 10⁰ S to 31⁰ N is chosen and open boundary condition is implemented at the southern and eastern part of the lateral boundaries for smooth exchange with the open ocean. Grid resolution is 0.25x0.25 ⁰ in horizontal and varies in vertical depth from 5m near surface to 500m near ocean bottom. Model is initialised from state of rest with an annual average Temperature and Salinity profile as background state and forced with 10 years climatology of daily average momentum flux from NASA JPL ECCO2 and heat fluxes from WHOI and precipitation from TRMM. At the lateral boundaries sea surface height anomaly is prescribed at 7 days interval to maintain the mass conservation. At lateral boundaries, vertical profiles of temperature and salinity are also prescribed at 5 days interval obtained from SODA. Model run is integrated for 10 years as spin up and then restarted for 5 years with instantaneous data from same source. The instantaneous 5-year output data is analysed to investigate the circulation and energetics in AS. It is observed that model very well represents the Somali current and south-eastward net water transport during summer monsoon and current reversal in winter monsoon with reversing winds and weak currents during boreal spring and fall. Salinity which plays dominant role in AS is also represented well in the model. Model produces a positive warm bias in the equatorial and south-western part of the domain which could be due to improper latent heat flux exchange. Investigation of Turbulent kinetic Energy (TKE) reveals that TKE is strong along Somali coast in summer monsoon and relatively weak in winter monsoon due to strong winds. Dissipation also shows strong signatures along Somali coast and quite strong features in equatorial region in winter monsoon. This indicates that AS is largely influenced by momentum flux exchange that in turn influences the energy budget.