冬季黄海暖流西偏机理数值探讨

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

利用海洋数值模式(MITgcm)模拟了冬季黄海流场并对冬季黄海暖流西偏的机理进行了探讨。冬季黄海流场模拟试验表明,黄海暖流由济州岛以西约32.5°N,125°E附近进入黄海,然后沿着黄海深槽西侧70 m等深线附近向北偏西运动;海面高度调整对黄海暖流路径具有重要影响,沿着黄海暖流路径的海面高度梯度比周围海区大,由海面高度梯度产生的地转流引起的北向体积输运占总的北向体积输运的78%。狭长海湾地形控制试验表明,单纯的黄海地形分布不足以引起黄海暖流西偏。黄海典型断面试验与渤海、黄海、东海地形控制试验说明,黄海暖流进入黄海的地理位置对流场分布有重要影响,黄海暖流进入黄海的位置恰好位于深槽西侧地形坡度较大区域,在位涡守恒的约束下黄海暖流受地形捕获沿70 m等深线附近向北偏西运动;试验还表明,黄海暖流进入黄海的位置与东海北部环流和地形分布有关,在冬季风的作用下东海北部环流的一部分沿着地形陡坡进入黄海形成黄海暖流。由此认为,黄海、东海环流在其特殊地形的约束下对冬季风的响应和调整,是引起黄海暖流西偏的主要原因。

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.