粤东及闽南近岸上升流对局地风场变化的响应

本文利用2010年6-7月的实测温盐、水位、海流等资料，结合风场数据，讨论了在台风影响较小的情况下，粤东及闽南近岸上升流对局地风场变化的响应特征，主要结论如下:（1）谱分析结果显示，沿岸风、水位、海流、近底层水温均具有3.5～4.0 d、5.0～5.5 d、8.3～9.0 d的波动周期，沿岸风的变化引起上升流强度在3～9 d周期上的波动；（2）上升流对局地风场变化的响应过程如下:利于上升流产生的局地风场发生变化时，沿岸风作用下产生的Ekman输运促使的上升流区水位的下降幅度发生改变，随即向岸方向的压强梯度力也发生变化，进而导致沿岸流及近底层向岸流的增强或减弱，而近底层向岸流强度的改变又会引起近底层水温的变化；（3）相关分析及交叉谱分析的结果表明，沿岸风的变化将在3 d以内影响上升流区近底层水温。以34 m向岸流代表近底层向岸流，则“沿岸风-水位-近底层向岸流-近底层水温”这一过程的响应时间依次为24 h、7 h、27 h左右。

Response of upwelling in eastern Guangdong and southern Fujian coastal seas to the local wind variation

Based on the cruise conductivity-temperature-depth(CTD) data, the sea level, current and near bottom temperature data from seabed-based observations, and the wind field data during June to July, 2010, this paper studied the response of upwelling in eastern Guangdong and southern Fujian coastal seas to the local wind variation, while the influence of typhoon was relatively weak. The main conclusions are as follows: (1) The results of power spectrum analyses showed that, the alongshore wind speed component, sea level, current and near bottom temperature showed similar variations with the significant periods of fluctuations in 3.5-4.0 d, 5.0-5.5 d and 8.3-9.0 d. The variation of alongshore wind speed component brought about the fluctuation of the upwelling intensity in 3-9 d frequency band. (2) The response process of upwelling to the local wind variation was like this. Surface water was transported offshore within the surface Ekman layer because of the alongshore component of wind stress. Coastal sea level dropped, a cross-shore pressure gradient set up. The pressure gradient would change following the local wind variation, resulting in enhanced(or weakened) alongshore current and enhanced(or weakened) near bottom cross-shore current. Near bottom temperature changed according to the variation of near bottom cross-shore current. (3) The results of correlation analyses and cross-spectral analysis showed that, the variation of alongshore wind speed component would influence near bottom temperature in upwelling zone within 3 days. The lag time for sea level''s response to alongshore wind variation, near bottom (34 m) cross-shore current''s response to sea level variation and near bottom temperature''s response to near bottom (34 m) cross-shore current variation were 24 h, 7 h and 27 h respectively.