Study Of Interaction Between Antarctic Circumpolar Current And Antarctic Coastal Current In The Indian Section Of The Southern Ocean

The interaction between Antarctic Circumpolar Current (ACC) and Antarctic coastal current in the Indian section of the Southern Ocean is investigated in this paper by using numerical and theoretical methods. Especially, The non-zonation of ACC in the region of Kerguelen Plateau and its annual variation are analyzed. Based on OPYC model, a coupled sea ice-ocean isopycnal numerical model of the Southern Ocean is established. Both dynamic and thermodynamic processes are included in this model. The forcing fields, including heat flux and fresh water flux, are calculated from monthly mean data(ECMWF). The model domain covers the entire Southern Ocean and the grids are variable so that a high resolution is available in the focus area. The simulated circulation and sea ice cover agree well with the observed data. The modeled mean transport through Drake Passage is I45Sv that is very close to the observed value (l34Sv) compared with the value by FRAM (200Sv). The simulated circulation displays some different patterns in the Southern Ocean due to the interaction between ACC and coastal current. In the Indian section, ACC is close to the coastal current so a number of eddies appear between ACC and the coastal current owing to the variations of coastal line and topography. This kind of interaction is a result of the non-zonation of ACC in the region of Kerguelen Plateau. ACC passes through the northern, southern and middle of the plateau separately. The interaction between the southern branch of ACC and the westward Antarctic Slope Current is the main part of the interaction between ACC and coastal current in this area. The southern branch of ACC bypassing the north part of the Kerguelen Plateau behaves like an annual variation while the southern one displays a semi-annual variation. The variations of both branches are consistent with the variations of the wind stress in bc~th regions. A theoretical analysis shows that the non-zonation of ACC in the region of Kerguelen Plateau is due to the changes in potential vorticity of the water column caused by the curl of the ratio of wind stress to topography. The bifurcation and turning of ACC is related to the curl distribution.