渤海夏季第一斜压罗斯贝变形半径的计算与分析

Calculation and Analysis of the First Baroclinic Rossby Deformation Radius in Summer in the Bohai Sea

利用渤海2006年夏季大面观测的CTD温盐资料,分别运用WKB近似和数值方法计算了渤海夏季第一斜压罗斯贝变形半径和第一斜压重力波相速度。结果显示,两种不同算法得出的斜压罗斯贝变形半径和斜压重力波相速度的分布格局相似,与渤海等深线分布大体一致。数值解法下,在北戴河和长兴岛附近海域,斜压罗斯贝变形半径较大,最大为4.72km,对应的斜压重力波相速度最大为0.44m/s;在莱州湾海域,斜压罗斯贝变形半径较小,最大仅为1.76km,对应的斜压重力波相速度最大为0.16m/s;在渤海中部斜压罗斯贝变形半径和斜压重力波相速度的等值线发生明显弯曲,在靠近渤海海峡内侧出现一个极小值,而与之对应在渤海中部以西出现一个极大值,导致变形半径的等值线呈NE-SW向倾斜的"S"状。渤海夏季第一斜压罗斯贝变形半径在WKB近似下的结果较低于数值解法求出的结果,这主要是因为,WKB近似依赖于浮性频率对水深的积分,适用于浮性频率垂向变化较弱的情况,渤海夏季浮性频率垂向变化较大,WKB近似得出的结果误差较大。

Based on observed temperature and salinity during the summer of 2006 in the Bohai Sea,the first baroclinic Rossby radius and the first baroclinic gravity-wave phase speed are calculated using WKB approximation and numerical method.The results indicate that the spatial distribution of the baroclinic Rossby radius and the baroclinic gravity-wave phase speed estimated by the two methods are very similar-both follow the isobath of the Bohai Sea.The result of numerical method shows that the maximum first baroclinic Rossby radius can reach 4.72 km in waters around Beidaihe and Changxing island with maximum phase speed of 0.44m/s.The minimum baroclinic Rossby radius and phase speed are found in the Laizhou bay,which are 1.76 km and 0.16m/s,respectively.In the central of the Bohai Sea,a minimum Rossby radius appears near the inner Bohai Strait,and a maximum value appears in the west side of the central Bohai Sea,causing the contour lines of the Rossby radius showing a＇S＇shape in NE-SW direction.The Rossby radius estimated by WKB approximation is smaller than numerical estimation,mainly because WKB approximation is applicable when the vertical variation of Buoyancy frequency is weak,which is not the case in the summer of the Bohai Sea.