南极绕极流线性理论的一个摄动解

A Perturbational Solution of Linear Theory forAntarctic Circumpolar Current

为了模拟南极绕极流区的流动,首先将环形条带区从Drake海峡处分开,并展成以经纬度为坐标的矩形区域。将模拟区划分为边界区和内部区。与Munk的大洋环流理论不同,在我们所考虑的线性化的涡度方程中保留了经向摩擦作用。这是基于绕极流流轴处的强剪切产生的经向摩擦项与β效应同等重要的判断。另外,内部区的北边界取为流线,而2个侧边界区的北边界视为南北水体交换的通道。基于巴西暖流穿过北边界流入和秘鲁寒流穿过北边界流出,以及常年有大于100Sv(平均约134Sv)的水体自西向东穿过Drake海峡的观测事实,引入了净通量条件。计算出了不同于Sverdrup流的更集中的内部区带状流的流线分布,这与观测大体一致。在Drake海峡处引入匹配条件,从而得到了完整的边界解。计算结果与理论分析指出,通过Drake海峡的流量远小于南极绕极流所带动水体的纬向通量是因为Drake海峡偏离绕极流流轴(也是南大洋西风带的主轴)。受南美大陆的阻挡,另一部分水体通过秘鲁寒流流出该海区。

To simulate the flow in the Antarctic Circumpolar Current (ACC) area, the annular strip area is cut first at the Drake Passage, then is spread into a rectangular area with the longitude-latitude coordinate, and the rectangular simulated area is divided into boundary area and interior area. It is different from the Munk's ocean circulation theory that we keep the meridional friction term in the linearized vorticity equation, which is based on the fact that the meridional friction term caused by the strong shear at the ACC's stream axis is equivalently important as the β effect term. In our simulation, the north boundary of the interior area is taken as a streamline, and the north boundaries of two boundary areas are considered as the passages for north-south water exchange. The introduction of the zonal net volume transport is based on the observed fact that the Brazil Warm Current flows in and the Peru Cold Current flows out through the north boundary ,and there is an eastward water transport of more than 100 Sv (about 134 Sv on an ave-rage) through the Drake Passage. It is shown from the computed results that the banded streamline distributions in the interior area are largely consistent with the observed ones, and the matching condition at the Drake Passage is introduced to obtain a complete boundary solution. It is shown from the computed results and theoretic analysis that the volume transport through the Drake Passage is much smaller than the zonal flux carried by ACC because the Drake Passage is deviated from the ACC's stream axis, and the other part of water volume flows out of the simulated sea area by means of the Peru Cold Current due to the blockage of the South America continent.