冬季大风事件下渤黄海水交换过程及其对渤海水体更新的影响

Water exchange and transport in coastal ocean is an important process relating to water quality problems,. Through advection and dispersion, coastal areas with active water exchange usually have good self-purification capability. .As a semi-enclosed coastal sea in the northeast China, Bohai Sea connects Yellow Sea through a narrow Bohai Strait. In the last decade, increasing pollution discharge combined with weak water exchange capability has induced many coastal environmental problems. Improved understanding of water mass exchange time in such a semi-enclosed coastal sea is very useful to quantify and mitigate aforementioned environmental issues. In the Bohai sea, the prevailing wind-driven currents dominant the total current during the wintertime is more a magnitude than tide-driven current which may be import factors to impact water exchange time. The winter storm event, a familiar synoptic phenomenon in winter of the Bohai Sea and Yellow Sea, has the important effect on the water exchange between the Bohai Sea and Yellow Sea..The research on the water exchange in Bohai Sea and Yellow Sea mainly focused on climate state before. However, recently based on observation we found that the most wind-induced current get to 60cm/s and then the sea level decline to 1m which shows that large amount of water fast exchange between Bohai Sea and Yellow Sea in a short time. So, this find ask us to research the water exchange in Bohai Sea and Yellow Sea from a new visual way. In this research, based on the dynamics theory, through the way of the data analyse and numerical simulation to research the water exchange. These reshearch make a groundwork to evaluate the physical self-purification capability in Bohai Sea.

以往对渤黄海水交换和渤海水体更新能力的研究主要关注气候状态下的过程。然而近期研究发现，大风过程产生的风海流最大流速达60cm/s，海平面平均下降近1m，大量水体短时间内在渤黄海内进行快速交换。此发现使我们必须从新的视角，研究渤黄海水交换过程及其对渤海水体更新的作用。.本项目将基于基本的动力学理论，采用资料分析和数值模拟手段，以水体年龄谱均值为指标，研究冬季大风作用下渤黄海水交换过程及其对渤海水体更新的影响，为准确评估渤海物理自净能力奠定科学基础。

冬季渤海海域大风频发，观测资料显示，大风事件发生时，海平面急剧下降约1m，渤海的出流流速高达0.6m/s，由大风事件而造成的短时间内渤、黄海间大量水体的交换。因此研究冬季渤海大风作用下环流调整过程是研究渤黄海水交换的基础之一。本研究以大风事件为切入点研究渤海水体输运的动力过程，并以水体年龄谱均值为水体年龄指标，定量计算大风事件下渤海的水体交换时间，评估大风事件对渤黄海水交换及水体更新的贡献。.大风事件下的渤黄海水交换过程，现场观测以及数值模式结果均显示，在大风爆发阶段，渤海水位下降，海水从渤海流入黄海，在大风衰退阶段，渤海水位回升，海水从黄海流入渤海，并且整个水交换过程伴随着开尔文波的传播调整。进一步的理论分析揭示了开尔文波影响渤黄海水交换的动力学机制。在大风爆发阶段，朝鲜半岛沿岸的开尔文波传入渤海导致整个渤海海平面下降，使得海水从渤海流入黄海，开尔文波被捕获在渤海海盆。在大风衰退阶段，开尔文波被释放而传出渤海，整个渤海海平面上升，使得海水从黄海流入渤海。因此，旋转效应下的开尔文波调整过程是影响渤黄海水交换的主要因素。.构建了渤海水龄模型，定量计算了冬季渤海水龄的分布并比较了高频风和低频风场作用下水龄的时空变化。研究了冬季渤海海域的平均水龄分布，发现水龄分布存在明显的空间结构。对于黄河口水体，辽东湾的水龄最长，莱州湾水龄最短。通过高频和低频风的不同强迫试验，发现莱州湾和渤海中部水体的水龄对风场响应敏感，而辽东湾和渤海湾响应较弱。通过对黄河口水体水龄的研究，使我们对渤海沿岸海域污染的输运有了初步认识，为排污口设置提供了一定的依据。.构建了渤海水体平均存留时间模型，定量计算了冬季渤海平均存留时间的分布并比较了高频风和低频风场作用对平均存留时间的影响。研究了冬季渤海海域的平均存留时间分布，并针对大风事件作用下各海湾的水体存留时间的变化进行分析，得出一次大风事件能提高渤海海水与外海的水交换，减少海水在渤海海域的存留时间。对于平均存留时间的模拟，是对海域内任意一点流出所关注区域所需时间的定量计算，为海上溢油时油膜扩散出关注海域所需时间提供一定的依据。