象山港内湾潮汐应变对横向流及其余环流垂向空间结构的调控研究

Regulation of tidal straining on vertical spatial structure of lateral currents and residual circulations in the upper Xiangshan Bay

中文关键词:  象山港  横向流  潮汐应变  大小潮

英文关键词:Xiangshan Bay  lateral currents  tidal straining  spring-neap tide

中文摘要:

      横向流 (垂直于海湾主轴方向的流动) 对横向动量以及物质分布具有重要影响。已往研究表明，潮汐应变对横向流的垂向空间结构具有重要的调控作用。但这种认识仅局限于强层化海区，弱层化条件下潮汐应变对于横向流空间结构的影响仍未可知。为此，本文以象山港为例，基于实测数据阐释了弱层化条件下潮汐应变对横向流及其余环流垂向空间结构的调控作用。结果显示，象山港内湾横向流的垂向空间结构随大小潮呈现出明显的变化规律。大潮时，潮汐应变现象明显，涨潮时较强的垂向混合使得横向流在高潮阶段呈现出一层结构；落潮时垂向混合较弱，横向流在低潮时呈现两层结构。小潮时，潮汐应变受到抑制，垂向混合在涨落潮时均较弱，因此横向流在高低潮阶段均呈现出两层结构。经过潮时均进一步得到的横向余环流呈现出上层向南、下层向北的两层结构。由于潮汐应变的大小潮变化，横向余环流的反转深度反转点自大潮到小潮呈现出上升的趋势。

英文摘要:

      Lateral currents (flow perpendicular to the main axis of the bay) have an important effect on lateral momentum and material distribution. Previous studies have shown that tidal straining played an important role in regulating the vertical spatial structure of lateral currents. The understanding is only limited to highly stratified sea areas, while the effect of tidal straining on the spatial structure of lateral currents under weakly stratified conditions is still unknown. In conclusion, this study taken Xiangshan Bay as an example to discuss the effects of regulation of tidal straining on the vertical spatial structure of lateral currents and residual circulations based on the in-situ data. The results showed that the vertical spatial structure of lateral circulation in the upper Xiangshan Bay presented obvious changes during spring-neap tide. During spring tide, tidal straining was apparent. Lateral currents presented one-layer structure at high tides due to strong vertical mixing but two-layer structure at low tides due to weak vertical mixing. During neap tide, the tidal straining was suppressed, and lateral currents presented two-layer structure during both high and low tides due to weak vertical mixing. Lateral residual circulations obtained from tidal averaging presented two-layer structure which was southward in the upper layer and northward in the lower layer. Due to the spring-neap variations of tidal straining in intensity, the reverse depth of lateral residual circulation ascended from spring to neap tides.