A Numerical Model Study Of Seamount-induced Local Physical Processes

A seamount is a common form in the seabed topography and is widely distributed in all oceans.Existing studies show that seamounts can induce various physical processes,and they influence the near and far field of seamounts.Based on previous studies,this research focuses on local physical processes induced by seamounts.These processes are analyzed in detail by using a 3D idealized seamounts model and a real seamounts model.On the other hand,the influence of seamount on ocean mixing is parameterized and applied to the Community Earth System Model(CESM).Its impact on the simulation results is analyzed.In this paper,the Regional Ocean Modeling System(ROMS)is used to build idealized seamount experiments.By comparing the experiments of seamounts with different heights,it is found that with the increase of the idealized seamount height,the influence of the seamount on the surrounding seawater gradually increases,but the Taylor cap is weakened.When the seamount's height exceeds a certain height,obvious and stable fronts in the bottom boundary appear on both sides of the seamount.The physical field structure around the bottom boundary layer front is also analyzed.It is found that the structure on both sides of the front in the bottom boundary layer is asymmetrical,and a vertical secondary circulation is formed on the right side of the incoming flow direction,but not on the other side.Moreover,the mixing on the left side is significantly greater than that on the right side.The vertical mixing around the seamount is analyzed,and it is shown that the sub-grid parameterized mixing is mainly caused by friction in the bottom boundary,which is 1-2 orders of magnitude greater than the contribution of shear instability.Within the grid resolution,the local physical processes induced by the seamount cause mixing on both sides and above the seamount,but this part of the mixing is not included in the sub-grid parameterization.As the model resolution decreases,this part of the mixing is underestimated or even ignored.Secondly,ROMS is used to simulate the effects of real seamounts on the ocean environment in the Northwest Pacific Ocean.The results show that fronts in the bottom boundary layer and Taylor cap are also found around the real seamount.In addition,similar to the idealized seamount model results,the sub-grid parameterization does not include the mixing induced by the fronts and Taylor cap.Finally,using Argo data,a global mixing coefficient is calculated by fine-scale parameterization.By fitting the mixing coefficient and topography roughness,the formula of topography roughness and mixing coefficient is obtained.The formula is then added to the CESM.After modifying the background mixing,the buoyancy frequency,the mixed layer depth and the seawater temperature of the model are improved.Furthermore,the improvement in the seawater temperature shows different characteristics at different depths.