太平洋风应力平均场的特征

THE FEATURES OF MEAN WIND STRESS FIELD IN THE PACIFIC OCEAN

本文利用迄今世界上最完善精细的全球综合海洋大气资料集（ＣＯＡＤＳ）提供的风场资料，计算了１９４９—１９８７年近４０年平均网格为５°×５°的太平洋海域逐月风应力场，并分析了各纬度带平均纬向和经向风应力的逐月变化以及１、４、７和１０月的风应力场的分布特征。风应力的计算采用整体空气动力学公式，其中曳力系数的计算是以Ｂｕｎｋｅｒ给出的曳力系数随风和海气温差变化的数表为基础，用最小二乘法，考虑了大气层结热力影响和风切变的动力影响，拟合了一个二次多项式。计算结果表明其精度和实用性都较好。

By using the wind data derived from COADS, of which the mesb is 5°×5°and the average period is from 1949 to 1987, monthly mean wind stress in the Pacific Ocean is calculated. For determining the wind stress, bulk aerodynamic formula is used in which the drag coefficient is represented by a second degree polynomial, considering the effect of wind speed and stability. The drag coefficient depending on wind speed and stability, which is proposed by Bunker, is selected for analysis. The results show this method is quite good for its precision and convience.In this paper, the zonal and meridional wind stess for each latitude zone and the distributions of wind stress field in January, April, July and October are analyzed. distribution of wind stress corresponds with planetary wind system on the whole. Walker cell in equatorial area and seasonal variation of monsoon circulation in the west Pacific have an obvious impact on the variation of wind stress. There are some asymmetries in the mean zonal wind stress of both hemispheres. Wind stress intensity of midlatitude westerlies is weaker in the northern hemisphere than in the southern hemisphere, and it is opposite in the tropical trades.In the northern hemisphere, in January, the zero line of zonal wind stress is at about 28°N. To the north of this line, the zonal wind stress is positive where the ocean gets momentum from the air.To the south of this line up to the 32°S. the zonal wind stress is negative where the air gets momentum from the ocean. Along the equatorial zone of the west Pacific between 0° 12°S, momentum flux is transferred from air to ocean. In July. trade-wind moves northward. The zero line of zonal wind stress is at about 40°N in the northern hemisphere and is at about 31°S in the southern hemisphere.The momentum flux is positive in the summer monsoon regions.The value of longitudinal wind stress is much lower than that of latitudinal wind stress. In January, the dominant wind in the subtropical and tropical north Pacific is from northeast. The meridional wind stress is negative whiers the ocean gets momentum from the dir. Along the east and south coast of Asia continent, the strong northeast monsoon results in a band which has maximum values of meridional wind stress. In July. the wind stress in the east Pacific of northern hemisphere is negative. In the west Pacific, the momentum flux is positive with a maximum in the south China sea and its adjecent seas related to the southwest and southeast monsoon there.