西南季风不同阶段南海北部珠江口外断面水文调查分析

根据2000年7月及2001年5月南海北部珠江口外断面CTD调查资料、同期气象资料,并结合该海域历史资料,对调查断面珠江冲淡水扩展范围、跃层变动情况及上升流特征进行了分析,观察到对应于夏季西南季风的不同阶段,调查断面跃层分布与珠江冲淡水影响范围均发生明显变动,升降流的影响也呈现出不同特征：(1)西南季风较强时,断面陆架区上表层受冲淡水影响明显,海区的层化结构明显加强;(2)西南季风较强时．调查断面出现上升流和下降流。研究结果表明：(1)局地风应力与热通量的变化控制了调查断面跃层或混合层的温度和深度的变化,影响着珠江冲淡水的扩展范围,西南季风较强时珠江冲淡水扩展范围变大,调查断面跃层或混合层强度变大,深度变深;(2)夏季西南季风强时调查断面存在上升流,其形成机制为风产生的离岸水体Ekman输运的补偿效应,底地形的变化虽然也造成较弱的外海次表层水涌升,但可能只是加强了上升的速度或强度;(3)夏季西南季风强时调查断面上存在上升流区与下降流区毗邻的现象,下降流成因可能有二,一为近岸流和陆坡流呈相反方向运动形成弱的反气旋涡,二为“上升与下降因相互水体补充的需要而共生”。

ANALYSIS OF HYDROLOGIC SECTION OFF ZHUJIANG RIVER ESTUARY IN NORTHERN SOUTH CHINA SEA DURING VARIOUS SOUTHWEST MONSOON PHASES

Based on the CTD data from two cruises off the Zhujiang River Estuary in the northern South China Sea in July, 2000 and in May, 2001, and combining with the meteorological data in the corresponding period as well as historical observations and modeling results in this area, some features at the observed section ZJ are discussed, including the diluted water from the Zhujiang River, spring layer and mixed layer, upwelling and downwelling. It was observed that these sectional hydrological features varied with different seasons: (1) with the strengthening of the southwest monsoon, the surface layer was influenced more intensively by the diluted water from the Zhujiang River and the stratification structure became more evident at section ZJ; and (2) there existed upwellings and downwellings at the section when the southwest monsoon was strong enough. Some conclusions have been reached as below. (1) Local wind and solar flux dominate the temperature and depth of the spring layer and mixed layer, and affect the extension of the diluted water from the Zhujiang River in a positive way. (2) The southwest monsoon plays the most important role in leading to the appearance of upwellings, which transport water across the shelf through the Ekman effect; the topography of the investigated section may enhance the intensity of the upwellings, but can not result in upwellings when the monsoon is weak. (3) The upwelling and downwelling areas coexist at the section when the southwest monsoon is strong. There may be two explanations on the appearance of downwellings, one is weak anticyclonic eddy resulted from the flows in opposite flowing directions along the slope and along the continent, and the other is that "the upwelling and downwelling coexist in need of the water complement".