南海盐度锋的年际变化特征分析

Inter-annual variability of salinity front in the South China Sea

为了探究南海表层5 m盐度锋的年际变化特征,应用50年(1958—2007年)的SODA月平均资料,采用均方差和经验正交函数进行研究。结果表明,盐度锋年际变化显著的区域集中在北部湾、海南岛以东、南海北部、吕宋海峡、东马来西亚西北部和越南最南端;第一模态和第二模态时间系数变化趋势均表明南海盐度锋强度在逐渐减小;前者呈单极子型空间分布,后者空间分布型则为偶极子型。第一模态时间系数功率谱分析表明该模态存在3—5年和7—16年的周期,Morlet小波分析显示1965—2000年该模态主要存在4年、9年和12年左右的周期。第一模态确立的3个负位相中心区域(海南岛以东、吕宋海峡和越南最南端)的均值变化趋势一致,强度都在逐渐增大,具有同位相变化特征;第二模态时间系数功率谱分析表明该模态存在3年、5年和8—12年的周期。Morlet小波分析表明1962—2001年期间该模态存在3年、5年和9—12年的周期。第二模态找出的两个正负位相中心分别在东马来西亚西北部和南海北部,前者盐度锋强度在逐渐减小,而后者强度却在持续增大,强度的年际变化呈现反位相变化特征。

Based on the 50 years SODA monthly data （1958--2007 years）, the standard deviation and empirical orthogonal function studies is used to investigate inter-annual variation of surface salinity front under 5 meters in the South China Sea. The results show that the area of the remarkable inter-annual variability of the salinity front concentrates in the northern Gulf, east of Hainan Island ＆ the northern South China Sea, the Luzon Strait, north-west of East Malaysia and northern South China Sea. The time series trends of the first mode and the sec- ond mode show that the intensity of salinity front is both decreasing. Spatial distribution type of the former is uni- polar and the latter is dipole. The power spectral analysis of the first mode time coefficients shows that there are 3 to 5 years and 7 to 16 years cycle. Morlet wavelet analysis shows that from 1965 to 2000 it mainly exists 4, 9 and 12 year cycle or so. The mean strength of three negative phase central region （Hainan Island, east of Luzon Strait and the southernmost tip of Vietnam） established by the first mode is gradually increasing, with the same phase variation trend. Power spectrum analysis of the second mode time coefficients indicate that the mode exists 3, 5 and 8 to 12 years cycle. Morlet wavelet analysis shows that during the period 1962 to 2001, there are 3, 5 and 9 to 12 years cycle. Two positive and negative phase center identified by second mode is respectively in northwest of Malaysia and the northern South China Sea, and the strength of the salinity front of the former is gradually reduc ing, but the latter increasing. The inter-annual variability of strength shows the anti-phase variability characteris tics.