南海北部陆架海域内潮特征的观测研究

利用2014年南海东沙岛西北部海域70余天的流速剖面高频观测资料,研究分析了该海区正压潮、内潮的时空分布特征。结果表明,观测海区正压潮流以O_1,K_1,M_2,S_2为主;斜压潮流中,除四大分潮之外,MU_2与2Q_1分潮能量也较强;内潮的主轴方向基本沿东南-西北方向,近似与局地等深线垂直。全日内潮的锁相部分占全日内潮能量的17.5%,而半日内潮的锁相部分占半日内潮能量的30%;进一步研究发现半日内潮主要由第一模态主导,而全日内潮第二模态占比50%,约为其第一模态能量的两倍;内潮模态能量占比显示出显著的大小潮调制的半月周期。对比不同垂向模态计算方法发现,当流速观测深度有限时,利用全水深温盐资料计算观测范围内流速垂向模态是更为准确的方式。

THE INTERNAL TIDES ON CONTINENTAL SHELF OF THE NORTHERN SOUTH CHINA SEA

The temporal variability and vertical distribution of barotropic tides and internal tides were investigated using 70-day high-frequency mooring data taken from continental shelf of the northwestern South China Sea in 2014. We found that the components of O₁, K₁, M₂, and S₂ were the most prominent ones in barotropic tides. While in baroclinic tides, additional to these major tidal components, MU₂ and 2Q₁ were considerably obvious. The major axes of tidal ellipses were in southeast-northwest direction, being almost perpendicular to the local isobaths extension. The coherent diurnal internal tidal currents took only 17.5% variance of total diurnal internal tidal variance, and the counterpart in semidiurnal tides covered 30%. Moreover, the semidiurnal internal waves were dominant by the first mode motion, whereas the diurnal internal tides exhibited higher mode features:the second mode covered a half of the total variance in diurnal tides, which is twice of the first mode''s variance. In addition, both the total variance and the modal structure featured a half-month variation. By comparing the different ways of calculating the vertical mode when observed depth of the velocity is limited, we found that calculating vertical mode using full-depth temperature and salinity data is more accurate.