南海西边界强流区季节和年际变化特征

Study on seasonal and interannual variation of the SCS western boundary strong current

基于1951—2010年SODA海洋同化数据资料,研究分析了南海西边界强流的季节及年际变化的特征,目的是为进一步探讨南海西边界强流的季节及年际变化机理奠定基础。分析研究发现:(1)南海西边界强流空间位置、水平和垂向范围及环流形态等季节变化明显,冬季环流形态空间位置稳定,强流一般9、10月份出现并开始加强,最强出现在12月份,1月份开始逐渐减弱。强流的水平范围一般为60—110 km,垂向范围在50—200 m之间,水平和垂向范围一般随着强流的增强(减小)而扩大(缩小);夏季环流形态变化较为复杂,强流空间位置不稳定,且逐步分裂成两支,一支移至近岸,一支在离岸原中心附近,分裂过程呈现由北向南推进的趋势,近岸支强度、垂向范围季节上没有明显变化规律,但北、中和南部有差别,北部分裂不明显且流速不大,南部分裂明显且近岸支流速较大;(2)南海西边界强流存在显著的年际变化,在转换月份上,夏季形态转换月份最早为2月份,最迟则到6月份,冬季形态转换月份最早为8月份,最迟则到11月份;流量输送上,冬季最大年份的达到23.3Sv,最小的年份流量只有1.5Sv,年际最大差异20Sv以上,夏季年际最大差异幅度也有10Sv以上;利用小波能谱分析南海西边界强流在年际变化上具有两个显著的准周期振荡:36个月(3 a)和大约99个月(8—9 a);(3)在1950年至2010年61 a时间段里,南海西边界流流量体积输送总体呈现出一种缓慢增加的趋势。

Based on SODA ocean assimilation data during 1951-2010, seasonal and interannual variation characteristics of the strong western boundary current in the South China Sea（SCS） are analyzed for a further examination on the variation mechanism of the strong western boundary current. The results show that, （1） the spatial position, horizontal and vertical scope, and circulation patterns of the strong western boundary current have an obvious seasonal variation characteristics. The spatial position of winter circulation patterns is stable, and the strong flow generally appear and begin to strengthen in September and October, and reach the strongest value in December, while it start to weaken in January. Intense horizontal range is generally from 60--110 km and the vertical range is between 50--200 m. The horizontal and vertical range is generally enhanced （reduced） with strong current and expand （shrink）. Summer circulation patterns have unstable spatial position, and divide into two, one moving toward inshore and another one staying in the near of the original center. Division process presents trends from north to south. There is a difference among the north, middle and south place, which shows the flow is not obvious division in northern, southern separatists and significantly and larger coastal tributaries speed. （2）The strong western boundary current in some areas has a significant interannual variation characteristic. The earliest time for summer pattern conversion is in February, and the latest time is in June, while the earliest time for winter is in August, and the latest time is in November. For the flow bulk transportation, there is a significant differences in different years. The maximum value in winter reached 23.3Sv, while the minimum value is 1.5Sv. The annual maximum amplitude difference in summer is more than 10Sv. There are two significant quasi-periodic oscillation about flow bulk transportation after wavelet energy spectrum analysis： one is 36 months （3 years） .the anther is 99 months （8-9 years ）. （3） Overall, the stream flow bulk of the strong western boundary current transport has a slow increase trend from 1951 to 2010.