Modelling the seasonal and spatial variation of Turbulent Kinetic Energy budget in the north-western Indian Ocean
Authors: Chauhan Rajesh , Behera Manasa , Balasubramanian Sridhar 
Published: March 2024

North-western Indian Ocean (NIO), especially Arabian Sea (AS), experiences intense seasonally reversing winds and undergoes a seasonal change in the turbulence energetics. Given the importance of Arabian Sea dynamics on the Indian monsoon, a numerical investigation was carried out to study the energy budget using MOM 5. Model domain is between 32 to 118&#8304; E and 28&#8304; S to 30&#8304; N and is forced with daily varying 10 year averaged atmospheric fluxes. Lateral open boundaries are prescribed with sea surface height anomaly (SSHA) in combination with radiation condition. Vertical profiles of temperature and salinity are also prescribed at lateral boundaries. Using the averaged forcing, model is run for 10 years as spin up and brought into equilibrium and then forced with 5 years inter-annually varying dataset, which is used for analysis. Though the model domain covers quite an extensive part of Indian Ocean, but our analysis is limited in the NIO between 8&#8304;S to 30&#8304;N and 32 to 82&#8304;E (hereafter called as Analysis domain). Model produced data is seasonally averaged into 4 seasons, DJF (December to February), MAM (March to May), JJAS (June to September), and ON (October-November). Currents are well represented by model and are validated with OSCAR currents. Ocean properties such as Sea Surface Temperature, Sea Surface Salinity and Mixed Layer Depth produced by model are within reasonable bias. The investigation of TKE indicates that it has seasonal and spatial preference. Depth averaged over 30m TKE, indicates that it is strongest in JJAS and DJF along the Somalia coast and equatorial region of NIO respectively. In MAM, TKE is strong in south-western AS, close to equator and in ON, a reminiscence of TKE is seen along the Western AS (WAS). Spatial average vertical profile of TKE for 3 regions, [1: 8&#8304;S to 30&#8304;N and 32 to 82&#8304;E (Analysis domain), 2: 4&#8304;S to 4&#8304;N and 56 to 82&#8304;E (Western Equatorial Indian Ocean, WEIO), and 3: 4 to 12&#8304;N and 45 to 55&#8304;E (WAS)] is shown. Analysis reveals that TKE is highest in upper 200m and decreases with depth, and in DJF, it is maximum in WEIO and least in WAS, but quite interestingly, after 150m till about 250m, TKE increases in WAS. This could indicate strong subsurface turbulent activity in WAS in DJF. In JJAS, TKE is almost 4 times that of DJF and is highest in WAS and least in WEIO. In WAS, turbulence produced due to buoyancy is suppressed by production flux being negative which indicates inverse energy cascade in DJF. In JJAS, production flux is strongly positive in WAS with negative production in the Great Whirl eddy and in the equatorial region. Turbulence is produced by buoyancy as well near horn of Africa, yet dissipation is weak in the said region, which could be due to strong positive transport. Production shows weak positive features in WAS and is strongly negative in equatorial region in MAM and ON. Buoyancy flux is negative in WAS in MAM and ON, indicative of stable stratification.