摘要
本文通过2007年8月15日至2007年9月6日对越南东部11°N～15°N,110°E～114°E海域观测获得的温、盐、密度和流速资料,结合Jason-1卫星高度计日平均资料对越南东部海域夏季的中尺度现象进行了分析和计算。
首先利用卫星高度计资料发现并分析该海区8月15日到9月6日之间出现的中尺度涡A、B的位置、范围和生消过程。冷涡A从8月15日出现到9月6日基本消失,中心位置在13.75°N,112.25°E,直径约120千米;冷涡B从8月26日开始到9月6日依然存在,中心位置在11.75°N,110.5°E,直径约150千米。进一步分析温、盐、密度和流速场的空间结构和分布特点,从而更全面阐明以上中尺度现象特征。
其次利用观测得到的空间3维密度场和绝对流速场,采用数值方法求解纽曼边界条件下的2维Omega方程,求得参考面上的绝对动力高度。对其进行垂向积分得到3维空间的绝对动力高度场,从而根据地转关系计算出整个计算空间的地转流场。冷涡A、B海区地转流场大体呈现气旋形态,在冷涡外沿地转流速可达1m/s。在地转流场中,根据狄利克雷边界条件下3维的Omega方程,可以诊断出相关海域的垂向流速大小和分布。一般来说,大洋内区的垂向流速量级约为O(10-2)m d-1。通过计算,发现由于中尺度现象的存在,使得相应海域的升降流场的强度大大增加。其中,冷涡A所在海域的垂向流速最大可以达到6m d-1;冷涡B的所在海域最大垂向流速最大可达15m d-1。数值求解Omega方程得到的垂向流速准确程度通常受到以下因素如:准地转关系假设;CTD数据处理过程中插值过程对密度场的影响;边界条件的选取和定义;海上调查观测过程的不同步性以及分辨率不够高等的影响。
Analysis and calculation were given based on Jason-1 satellite altimetry, CTD and ADCP data, which were sampled from Aug. 15 to Sept. 6 in the 2007 Summer Cruise within the area 11°N～15°N, 110°E～114°E.
Satellite altimetry data were used to determine the locations, scales and life-spans of the mesoscale eddy A and B, respectively. Cold eddy A which lasted from Aug. 15 to Sept. 6, merged at 13.75°N, 112.25°E with a diameter around 120km. On Aug. 26, cold eddy B show up at 11.75°N, 110.5°E with a diameter about 150km. Further description to the characteristics of those two mesoscale eddies were carried out based on the analysis of spatial structures of temperature, salinity, density and absolute velocity fields.
3-D density and absolute velocity field were used to obtain the absolute dynamic height field via the numerical solution of 2-D Omega equation. The geostrophic velocity field was calculated due to the geostrophic balance. Geostrophic velocity field is generally cyclonic pattern. At the outskirt of gyre, geostrophic velocity was up to approximately 1m/s. Given the 3-D geostrophic velocity field, velocity of vertical circulation could be diagnosed using 3-D Omega equation. Usually vertical velocity in the inner ocean owned the magnitude of O(10-2 ) m d-1. But due to the presence of mesoscale eddies, vertical velocity here was up to 6m d-1 and 15m d-1 at cold eddy A and B, respectively. The accuracy of the vertical velocity could be impact by following aspects, such as, the assumption of quasi-geostrophic balance, the interpolation of raw density data, the choice of boundary conditions and the assumption that each survey was a synoptic one with high resolution.
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