30°N两侧东海海平面的低频变化及其与ENSO的关系

CHANGE OF MEAN SEA LEVEL OF LOW-FREQUENCY ON EAST CHINA SEA AND ITS RELATION WITH ENSO

利用1992年12月—2007年5月的高度计资料,研究东海海平面的变化特征。分析表明,近14年来长江口海域及30°N以南东海海平面的平均上升高度分别为57.7 mm和40.9 mm,各海域的海平面上升速度不完全相同。研究发现,东海海平面与南方涛动指数(SO I)二者的低频分量具有明显的相关关系,东海海平面显著受SO I调制,但30°N两侧海域SLA与SO I的相关性相反。东海纬向风应力与当地SLA、SO I具有很好的相关性;大气环流的辐散带两侧风场的差异,导致两侧海域平均SLA与纬向风应力距平的低频分量之间的相关关系不同(30°N以南的海域二者呈负相关性,长江口海域则呈正相关性)。将坐标系进行旋转后,获得与当地海平面异常相关最大的风应力方向。对SLA与新坐标系下风应力距平u的低频分量分析发现,长江口海域、30°N以南东海对海平面影响最大的风应力距平u方向分别为东偏南70°、东偏南23°。风应力距平u分量与SLA、SO I的低频分量呈现更好的相关性,由于辐散带在大气环流中的调制作用,导致30°N两侧海域海平面和风应力距平u对SO I响应相反。ENSO通过大气环流过程对东海海域的风场产生影响,当地风场通过纬向风应力对东海海平面的年际变化产生调制作用。因此,ENSO可以通过风应力对东海海平面产生影响。

On the basis of the sea level anomalies （SLA） altimeter data provided by CNES, the mean sea level change on the East China Sea was investigated. In recent 14 years, the rising rates have reached to 0.412 cm/a, 0. 292em/a respectively in the northern part and southern part of East China Sea separated by 30°N obviously,they are different. Correlative analysis shows that low frequency components of SLA have good but opposite response to that SOI and zonal wind stress anomalies, over the northern part and southern part of East China Sea. It is obvious that the sea level variation is closely related to SOI and zonal wind stress anomaly and it indicats that sea level in the East China Sea is dominated by E1 Niuo, as well as zonal wind stress. There is also a good relationship between SOI and the wind field over the East China Sea, of which the low frequency components are corresponding to ENSO. By using correlative analysis between SLA and wind stress anomalies u component in the new coordinate systern, it is found that the direction of wind stress most strongly affecting the sea level is 70 degrees and 23 degrees south of east separately, over the northern part and southern part of East China Sea. The divergence zone affects the wind field of the East China Sea strongly by atmospheric circulation, and that makes SLA and wind stress anomalies response differently between the northern part and southern part of the East China Sea. Based on the analysis above, a conclusion could be drawn that zonal wind stress affects the sea level significantly, indicating that ENSO impacts on wind filed of the East China Sea by means of atmospheric circulation, hence affecting the sea level. To sum up, ENSO and wind stress contribute to the sea level change over the East china Sea. In detail, ENSO impacts on wind filed of the East China Sea, hence affecting the interannual change of sea level, and sea surface wind responses well to ENSO, showing that ENSO could affect the sea level of the East China Sea, through mechanism of wind stress.