近50余年来南海西沙海域冬季风强度的变率

The Variability of Winter Monsoon Intensity in Xisha Waters, South China Sea for the Last More Than 50 Years

采用南海西沙永兴岛海洋观察站1958～1997年12～2月实测的北东向冬季风风速的平均值作为冬季风强度指数(WMI),与南海北缘滨珊瑚的相应年月份的实测δ18O平均值进行相关分析,得到线性回归方程WMI(m/s)=-4.913-2.138δ18O(‰),r=0.83,n=40.在计算(后报)所得的1944～1997年代际变化序列中,WMI在40～60年代呈下降趋势,70年代略有上升,而80～90年代又呈下降趋势.在年际变化序列中,WMI呈显著的下降趋势,所得线性回归方程为WMI=79.67-0.0377 Year,r=0.68,n=54.由斜率看出,WMI每10年平均下降约0.4 m/s.用Daniell功率谱法分析,近54年来WMI的变化存在2.5～7年的周期,与季风的QBO周期为2～2.4年,以及ENSO活动的3～8年周期密切相关.WMI连续下降的趋势是与全球持续变暖相映,南海海域冬季风强度的变化受到了全球变化的制约.

We have used correlative analysis between 1958-1997 mean December-January- February NE winter monsoon velocities, measured at the Yongxing Island Observatory, as a winter monsoon intensity index (WMI) and mean δ18O data for corresponding months from Porites lutea coral, collected in the northern part of the South China Sea, to obtain a linear equation: WMI (m/s) = -4.913-2.138δ18O (‰), r = 0.83, n = 40. The high correlative coefficient between the above-mentioned two series of WMI and δ18O data is made by using high-pass filtering method. On the basis of the calculated WMI sequence from 1944 to 1977, the interdecadal variability shows that the WMI series decreases in the 1940s-1960s, slightly increases in the 1970s, but decreases again in the 1980s-1990s. The interannual variability reveals that the WMI series decreases obviously from 1944 to 1977 with the correlative equation of WMI (m/s) = 79.69-0.0377 Year, r = 0.68, n = 54. The linear slope is negative, which means that the WMI series decreases by about 0.4 m/s every 10 years. The power-spectral analysis displays that a 54-year WMI series is provided with periodicity of a 2.5-7 year band, which is related to the QBO band of 2-2.4 years and ENSO band of 3-8 years. Therefore, it can be considered that the winter monsoon variability in the South China Sea is also controlled by the global change.