南海海盆中尺度涡移动速度统计分析

基于1993-2017年卫星高度计数据得到的中尺度涡追踪产品，分析了1000 m以深南海海盆中尺度涡移动速度C的时空分布特征。结果表明，南海海盆气候态平均的中尺度涡纬向移动速度c_x均为西向，经向移动速度c_y在海盆西北侧为南向，东南侧为北向。c_y随经度的变化与背景经向流的变化一致，相关系数达0.96，而c_x的变化与背景纬向流和β效应有关。c_x和C存在明显季节变化，夏季最慢，冬季最快。年际变化上，c_x和c_y的大值多发生在太平洋年代际涛动（PDO）负位相期的La Nina年。中尺度涡在其生命周期的开始和结束阶段（即生成和耗散阶段）移速较快，而在稳定的“中期”阶段移动缓慢。该趋势与涡旋转速呈反相关，相关系数为-0.93。以移速小于1.5 cm/s和大于15.4 cm/s定义的极慢和极快涡旋，分别占总涡旋数量的1.5%和1.9%。移速极慢的涡多出现在海盆的中部，且主要发生在夏季；移速极快的涡多出现在海盆的边缘，且主要发生在冬季。机制分析显示，南海海盆中尺度涡移动速度的时空分布受到大尺度背景流场调制。

Statistical analysis of mesoscale eddy propagation velocity in the South China Sea deep basin

Using mesoscale eddy trajectory product derived from satellite altimetry data from 1993 to 2017, this study analyzes the statistical characteristics of spatiotemporal distribution of mesoscale eddy propagation velocities ( C ) in the South China Sea (SCS) deep basin with depths >1 000 m. Climatologically, the zonal propagation velocities (c_x) are westwards in the whole basin, and the meridional velocities (c_y) are southwards in the northwestern basin, and northwards in the southeastern basin. The variation of c_y with longitude is consistent with that of the background meridional currents with correlation coefficient R2 of 0.96, while the variation of c_x is related both to the background zonal currents and β effect. The propagation velocities characterize significant seasonality with the minimum magnitude occurring in summer and the maximum in winter for c_x and C . Interannually, larger values of c_x and c_y mostly occurred in La Ni?a years in the negative phase of the Pacific Decadal Oscillation (PDO). Mesoscale eddies move fast at the beginning and end of their life span, i.e., at their growth and dissipation periods, and slowly during their stable “midlife” period. This trend is negatively correlated with the rotating tangential velocity with R2 of –0.93. Eddies with extreme propagation velocities are defined, which are slower (faster) than 1.5 cm/s (15.4 cm/s) and take 1.5% (1.9%) of the total eddies. The extremely slow-moving (fast-moving) eddies tend to appear in the middle (on the edge) of the basin, and mostly occur in summer (winter). The mechanism analysis reveals that the spatiotemporal distributions of the propagation velocities of mesoscale eddies in the SCS are modulated by the basin-scale background circulation.