强寒潮影响下浙江近海余水位变化的数值模拟

Numerical Study on the Variation of Residual Sea Level in Zhejiang Adjacent Seas Under Strong Cold Waves

  • 摘要: 寒潮对浙江近海余水位的影响不可忽视,本文旨在探究强寒潮影响下浙江近海余水位的变化规律和有关机制,为河口海岸寒潮过程的深入研究及防灾减灾工作提供参考。基于ROMS(Regional Ocean Modeling System)构建了渤、黄、东海高分辨率数值模型,并对浙江近海尤其是舟山群岛附近海域进行了网格加密。将该模型应用于研究2016年1月浙江近海对一次典型寒潮过程的响应。利用多处验潮站的调和常数及实测水位数据,并结合敏感性数值实验的结果,确定了适用于研究区域的风场数据、风应力拖曳系数和底摩擦系数。数值实验结果揭示了在寒潮影响下浙江近海余水位的空间变化规律。在寒潮影响下,从杭州湾到舟山群岛海域的余水位变化幅度可高达0.6 m。寒潮风的风速、风向及浙江沿岸复杂地形对寒潮期间余水位的时空分布起着重要作用,而余水位的变化比寒潮风速的变化略有时间滞后。此外,还揭示出浙江近海余水位对寒潮风的响应表现出明显的空间变异性:在台州至温州外海,余水位的增减幅度与寒潮风速呈正相关,两者的相关系数大于0.65;杭州湾余水位主要受纬向风应力的影响,两者之间呈现负相关关系,相关系数为0.53~0.65;而舟山群岛附近海域的余水位变化则受到风速、风向和地形等因素更为复杂的影响。在强寒潮影响下,浙江近海余水位的变化是风应力引起的Ekman输运和北风减弱后激发的开尔文波共同作用的结果。

     

    Abstract: The impact of cold waves on the residual sea level in adjacent waters near Zhejiang cannot be ignored. This study focuses on the patterns of residual sea level change and associated mechanisms during strong cold wave events, aiming to provide insights into how the cold waves affect coastal and estuary processes and to provide theoretical support for marine disaster prevention and mitigation. A high-resolution numerical model is developed with ROMS for the Bohai Sea, Yellow Sea, and East China Sea with mesh refinement in Zhoushan Islands area. The model is employed to study the sea level response to a typical cold wave event in Zhejiang adjacent seas during January 2016. By analyzing harmonic constants of multiple tidal stations and measured sea level data, the best combination of wind field data, wind stress drag coefficient, and bottom friction coefficient for the study area is determined through sensitivity numerical experiments. The simulation results well capture the changes of residual sea level during the cold wave events, which are verified with observational data from coastal tidal gauges. The study revealed spatial variation patterns of residual sea levels in Zhejiang adjacent seas. Under the influence of cold waves, the amplitude of variation reaches up to 0.6 meters from the Hangzhou Bay to Zhoushan Islands. The spatiotemporal distribution of residual sea level during the cold wave transit period is significantly influenced by cold wave wind speed, wind direction, and the complex terrain along the Zhejiang coast. The change in residual sea level lags that in cold wave wind speed by approximately 1 day. Significant spatial variability is observed in the response of residual sea level to cold wave winds. Sea level fluctuations off Taizhou and Wenzhou show a positive correlation with the cold wave wind speed with correlation coefficients exceeding 0.65. In contrast, in the Hangzhou Bay it exhibits a negative correlation between wind speed and residual sea level with correlation coefficients ranging from 0.53 to 0.65. Near the Zhoushan Islands, complex correlations between wind speed and residual sea level are also noted. The variation in residual sea level near the coast of Zhejiang Province is attributed to two main factors, the Ekman transport induced by wind stress and the Kelvin waves triggered by the weakening of northerly winds.

     

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