热带风暴天鹰期间南海西北部海域内部响应的观测分析

Response of the interior water column over the northwestern South China Sea during Washi

2005年7月28日热带风暴天鹰(Washi)在南海东沙群岛西南海域生成,并向西北偏西推进,在7月29日增强为一个热带风暴,于7月30日在海南岛登陆。布放在南海西北部大陆架海域的锚系测站记录了天鹰过境期间温度和海流的响应过程。分析结果表明,伴随着热带风暴的强风应力引起强烈的垂向混合作用,使海表面温度下降2℃,混合层加深20 m,并且8 m以下各水层也都有明显的降温过程,但降温幅度低于8 m层,降温开始的时间也随着深度的增加而延后。台风过后,观测海域的近惯性内波显著,其频率为8.1×10?6 Hz,略高于当地的惯性振荡频率(7.75×10?6 Hz)。滤波后的海流数据分析显示,近惯性波动是从海面向深海处传播的,其影响大约持续了10 d。本研究丰富了南海在台风期间响应过程的认识,可为近海海洋工程设计提供科学依据。

In July 2005, tropical storm Washi, which originated from the southwest of Dongsha Island in the South China Sea, moved towards northwest by west, intensified into a tropical storm on July 29, and finally landed on the Hainan Island on July 30. A mooring buoy deployed over the northwest shelf of the South China Sea recorded the res- ponse of temperature and current during this period. The results revealed strong vertical mixing induced by strong wind force, making the sea surface temperature decreased by 2 ℃ and depth of mixed layer deepened by 30 m. The layer below 8 m also displayed apparent cooling phenomenon, with less decreasing amplitude. The beginning of the cooling feature lagged with the increase of the depth. After the passage of Washi, the motions of internal waves were dominated by inertial oscillations, with the frequency around 8.1 ×10^-6 Hz, which was higher than the local inertial frequency （7.75×10^-6 Hz）. Band-filtered currents indicated that inertial oscillation propagated from the sea surface to the deep layer and lasted about 10 days. This study offers more understanding about response of ocean to typhoons in the South China Sea and can provide scientific basis for ocean engineering.