南麂岛附近海域潮汐和潮流的特征

以2008年冬季在浙江近海南麂岛附近投放的4个底锚系观测的水位和流速资料为依据,分析了潮汐和潮流特征。水位谱分析结果显示半日分潮最显著,全日分潮其次;近岸的浅水分潮比离岸大。水位调和分析结果表明:潮汐类型均为正规半日潮,近岸处的平均潮差大于3m,最大可能潮差大于6m,潮汐呈现出显著的低潮日不等和回归潮特征。流速谱分析结果显示半日分潮流最强,全日分潮流其次,且比半日分潮流小得多;近岸浅水分潮流比远离岸显著。流速调和分析结果表明:潮流类型均为正规半日潮流,靠近岸的两个站浅水分潮流较显著;最显著的半日分潮流是M2分潮流,其最大流速介于0.32～0.48m/s之间,全日分潮流均很弱,最大流速小于0.06m/s。M2分潮流均为逆时针旋转,椭圆率越靠近海底越大;最大分潮流流速分布为中上层最大、表层略小、底层最小;最大分潮流流速方向的垂向变化很小,底层比表层略为偏左;最大分潮流流速到达时间随深度的加深而提前,底层比中上层约提前30min。潮流椭圆的垂向分布显示这里的半日分潮流以正压潮流为主;日分潮流则表现出很强的斜压性。

Harmonic analysis of tide and tidal current near Nanji Island, Zhejiang Province

Based on the observed water level and current data during the winter of 2008 at four bottom-moorings near Nanji Island, Zhejiang Province, the characteristics of tide and tidal current are investigated with spectral and harmonic analysis. Spectral analysis of the water level shows that the semi-diurnal tides are the most significant constituents, followed by diurnal tides, shallow water tides at inshore area are significant than that in offshore. Harmonic analysis of the water level shows that the tide is regular semi-diurnal tide, the average tidal range is over 3 m and the potential maximum tidal range is greater than 6m at inshore area. The tide has significant low tide daily inequality and tropical tide characteristics. Spectral analysis of the current shows that the semi-diurnal tidal currents are the most significant constituents, followed by diurnal tidal currents which are much weaker than the former, shallow water tidal current at inshore area is much more significant than that in offshore. Harmonic analysis of the current shows that the tidal current is regular semi-diurnal tidal current, the most significant semi-diurnal tidal current constituent is M₂, with its maximum speed of 0.32-0.48 m/s,the most significant diurnal tidal current constituent is K₁, with its maximum speed less than 0.06 m/s. The M₂ tidal current rotates counter-clockwise, with increasing of its ellipticity as approaching to the sea floor. The maximum speed of M₂ tidal current occurs at middle and upper layers, decreases towards the surface and the sea floor. The direction of the maximum tidal current of M₂ does not vary significant with depth, except that the direction deviates slightly to the left near the sea floor. The timing of the maximum current advances when approaching to the sea floor, with about 30 minutes ahead at the bottom layer than the above layer. The semidiurnal tidal current is barotropic dominate with vertical homogeneous, while the diurnal tidal current shows a baroclinic property with a strong vertical variation.