Numerical Study Of Flow Passing A Deep Water Seamount: The Caiwei Seamount In The Northwest Pacific Ocean

The seamount is a terrain widely present in the ocean,and because it is completely submerged in the ocean, there are many special dynamic mechanisms around the seamounts. From the point of view of fluid mechanics, the flow passing the seamounts belongs to the classic problem of flow passing an obstacle, and many scholars have studied this problem under the ideal state. For the real seamount which has complex terrain, there are some hydrological observation and model simulation studies have been carried out these years, but the numerical simulations for the deep water seamount are very few. The Caiwei seamount which locates in 6000m of the northwest Pacific is such a deep water seamount. In this paper, based on the simulation of ideal seamount and the simulation of the Caiwei seamount in the real situation, the problem of flow passing the Caiwei seamount is studied and analyzed.This paper uses the regional oceanic modeling system (ROMS) to construct an ideal model of flow passing a seamount whose seamount is a quasi-cylinder whose size is designed according to the spatial scale of the Caiwei seamount and the uniform incoming flow is based on the characteristic flow velocity of the currents around the Caiwei. The simulation results show that the vorticity evolution near the ideal seamount exhibits different patterns with the increase of depth, and the vorticity in the surface will propagate downstream and not in the deeper layer. The flow above the ideal seamount exists a clockwise rotation with a period of about 4.5 days. The density around the ideal seamounts changes significantly in the upper layer,enhancing the stratification there.Then we employ the ROMS to simulate the flow passing the Caiwei Seamount during the period of a field experiment in 2012 - 2014. The China Ocean Mineral Resource R&D Association has extensively investigated the Caiwei seamount and measured the temperature and salinity and flow field around the Caiwei seamounts,provides us the CTD (conductivity temperature and depth instrument) and mooring system observation data. The comparison between the model results and the observed data shows that the simulation results generally reproduce the temperature and salinity profiles and current of the Caiwei seamount and verify the credibility of the simulation results. The simulation results show that there exist the Taylor column phenomenon above the seamounts, and reveals a clockwise gyre around the seamount in the bottom layer of the ocean. The analysis of the deep eddy actions in the simulation results shows that the anti-cyclonic eddy produced downstream of the seamount will not fall off in situ, and the cyclonic eddy will move along the edge of the seamounts along the clockwise. The momentum balance around the seamount are analyzed and it is found that nonlinear terms are important at the edge of seamount but the geostrophic balance is dominant in areas away from the seamount, the bottom friction cannot be ignored with the range of 50m from the bottom.Topographic Rossby wave with about 20 days period are founded around the seamount in the deep ocean layer and it propagates along the seamount clockwise.The high-resolution numerical product also reveal submesoscale phenomena in the deep ocean.