胶州湾水交换及湾口潮余流特征的数值研究

Numerical study of water exchange in the Jiaozhou Bay and the tidal residual currents near the bay mouth

利用基于普林斯顿海洋模式建立的胶州湾及临近海域潮汐潮流数值模型,结合胶州湾口走航式声学多普勒海流剖面仪(ADCP)测流资料,研究了胶州湾口的潮(余)流特征,并在潮流模型的基础上耦合建立了水质模块,模拟了胶州湾的水交换过程。考虑M2,S2,K1,O1,M4和MS4六个主要分潮,胶州湾口潮流场的模拟与ADCP观测数据吻合较好。外湾口水道上的潮流非常强,大潮期间观测到201 cm/s的峰值流速。团岛岬角的两侧分别存在一个流向相反的余流涡旋,两涡旋在团岛附近辐合,形成了57 cm/s的离岸强余流。整个胶州湾平均水体存留时间为71 d,平均半交换时间为25 d。胶州湾水体交换能力在空间分布上有很大差异:湾口海域最强,向湾顶逐渐减弱。湾内存在两个弱交换区,分别位于湾的西-西南部和东北端,水体存留时间多超过80 d,湾西局部水域最长达120 d,而半交换时间也大多超过40 d。潮流场的结构、强度,以及与湾口距离的远近是造成湾内水交换能力空间差异的主要原因。

A barotropic tidal model covering Jiaozhou Bay （JZB） and Qingdao coastal waters is developed based on Princeton Ocean Model （POM）. This numerical model, combined with the field survey currents data obtained from a vessel-mounted Acoustic Doppler Current Profiler （ADCP）, is used to investigate the characteristics of the tidal currents near the mouth of JZB. Furthermore, a water quality sub-model is coupled into the tidal model to simulate the water exchange processes in JZB. The tidal model includes six main tidal constituents （M2, S2, K1 , O1, M1, and MS4 ）, and reasonably reproduces tidal current field which is consistent with ADCP observation. The tidal current in the bay mouth channel is very strong. The observed peak current speed during spring tide period was 2.01 m/s. A couple of tidal residual eddies are found at both sides of the headland of Tuandao. The residual eddies converge near Tuandao, forming an offshore jet current of 57 cm/s. The modeled mean water residence time （WRT） in JZB is 71 days, and the mean half-life time （HLT） is 25 days. The horizontal distributions of WRT and HLT are quite uneven in space： they increase from the mouth to the top of JZB. The lowest water exchange rates are found in two regions, the west-southwest part and the northeastmost part of JZB, where the WRT is above 80 days with a maximum of 120 days, and HLT mostly exceeds 40 days. Such spatial distribution differences are controlled by the structure of tidal （residual） currents as well as the distance from the bay mouth.