Numerical investigation on the mechanism of the westward shifting of the Huanghai Warm Current

The mechanism of the westward shifting of the Huanghai Sea(Yellow Sea) Warm Current (HSWC) is studied through a group of numerical experiments using MIT General Circulation Model (MITgcm). The simulated wintertime Huanghai Sea circulation indicates that after the HSWC enters the Huanghai Sea domain around 32.5°N, 125°E to the west of the Cheju Island, it heads northwestward along the 70 m isobaths to the west of the Huanghai Sea trough. The sea surface height distribution also shows that along the path of the HSWC the sea surface height gradient is greater than the adjacent areas. The northward volume transport induced by the geostrophic current explains 78% of the total northward volume transport, the adjustment of the sea surface height is important to the path the HSWC. The topography control experiments conducted under the elongated semi-enclosed basin show the upwind flow goes along the deep trough regardless of the location of the deep trough, in the central of the basin or sideways. This means the deviation of the Huanghai Sea trough is not sufficient to make the HSWC shift to the west.The experiments performed with the topography of the typical section chosen in the Huanghai Sea tell the position where the HSWC enters the Huanghai Sea is crucial. The HSWC enters the Huanghai Sea domain along 50~70 m isobaths where the topography gradient is greater than adjacent areas. The topography gradient then traps the HSWC to flow along these isobaths. The position where the HSWC enters the Huanghai Sea domain is also related to the sharper topography gradient of the northern East China Sea.The site specific sharper topography gradient influences also the shelf circulation of the northern East China Sea. Under the strong winter monsoon, a part of the East China Sea shelf circulation enters the Huanghai Sea and becomes the HSWC. Therefore, the adjustment of the circulation in the East China Sea and Huanghai Sea under the winter monsoon together with the topography leads to the westward shifting of the HSWC which is trapped along the sharper topography gradient under the constrain of the conservation of the potential vorticity.