南海吕宋海峡21°N附近多潜标观测的上层海流

THE UPPER OCEAN CURRENTS OBSERVED BY MULTIPLE SUBSURFACE MOORED BUOYS ALONG 21°N NEAR LUZON STRAIT IN THE SOUTH CHINA SEA

为了了解潮流从西北太平洋经吕宋海峡进入南海内的变化及其垂向结构,本文利用在吕宋海峡附近沿东西方向布放的多套潜标同步获得的高分辨率ADCP长时间连续观测上层海流资料,使用调和分析方法将实测海流分解成3部分:不随时间变化的定常流、周期性潮流和剩余流,并将潮流分解为正压潮流和斜压潮流。通过对实测海流中各组分的分析,得到以下结论:该区域潮流类型在不同深度上有明显变化;M2潮自吕宋海峡传入南海后强度显著减弱75%左右,K1、O1分潮在上层强度减弱约三分之一。从垂向变化来看,在潮流强度上,各站点垂直方向上潮流强度均发生变化。从方向上看,各分潮潮流椭圆东西向特征明显,长轴变化较大,短轴(南北向特征)垂向变化不显著;潮流运动主要沿逆时针方向,垂直方向上潮流明显减弱或增强时会发生转向。斜压潮流主要集中在上表层,100m左右以下随深度逐渐减弱。东西方向斜压潮流能量比正压潮流强,而南北向的流比较稳定,且斜压潮流能量远小于正压潮流。定常流强度在各站点呈现相似的变化趋势,随深度变化减弱。

To understand the changes and the vertical structures of the tidal currents flowing from northwestern Pacific to the South China Sea through the Luzon Strait, long-term successive ADCP（acoustic Doppler current profiler） data were analyzed in harmonic analysis method. The data were recorded by five subsurface moored buoys along 21°N near Luzon Strait in the northern South China Sea. The ocean currents could be decomposed into steady current, residual current, and periodical tidal currents, and further into barotropic and baroclinic ones. The statistical characteristics of the current components showed that the type and velocity of tide vary vertically. When propagating from the western Pacific into the South China Sea through the Luzon Strait in the upper ocean, the intensity of M2 tide decreases to about 75%, and those of K1, O1 tides decreases to about 33%. The tidal ellipse of every tidal component is obviously in east-west direction; the long axis（east-west） is more variable that the short axis（north-south）. The baroclinic tidal current is stronger in the upper layer and gradually decreases below the depth of 100 m. For the east-west component, the energy of the baroclinic is stronger than the barotropic tidal current. For the north-south component, the energy of the baroclinic is much less than the barotropic tidal current. The velocity of steady current has a similar vertical structure in each observation station and decreases with depth.