IOCAS-IR
中国近海寒潮影响下的灾害性海洋动力环境研究
莫冬雪
第一作者单位中国科学院海洋研究所
学位类型博士
导师侯一筠
2018-05-15
学位授予单位中国科学院大学
学位授予地点中国科学院海洋研究所
学位名称理学博士
学位专业物理海洋学
关键词寒潮 风暴潮 海浪频谱 数值模拟 中国近海北部
摘要

寒潮,作为一种灾害性天气过程,伴有剧烈的降温、升压和大风,具有突发性、风时长、方向性强等特征。中国近海北部(包括渤海和北黄海)是一个水深较浅的半封闭海域,是全球受寒潮灾害影响最为严重的海域之一。当寒潮过境时,中国近海北部会产生显著而持续的水位升高和巨浪,对人类生活和航运造成严重影响,危害我国沿岸经济发展。本论文通过资料诊断、统计分析和数值模拟等多种手段,开展了对中国近海寒潮影响下的灾害性海洋动力环境的形成机制、发展规律和测报方法研究。

首先,基于气候预报系统再分析数据CFSR,本文对2001年至2010年渤海及北黄海受寒潮大风的入侵天数进行统计,证明寒潮主要在冬半年入侵中国近海,且主要为冷锋型天气系统。通过对寒潮大风风向和风速的统计,得到其主要风向和风速的时空分布情况。结果表明,寒潮大风存在明显的季节变化,风向以偏北风为主,其中东北大风的发生频率和风速都高于西北大风。

其次,本文基于区域海洋模式ROMS构建用于研究中国近海寒潮风暴潮的数值模式,对两次典型寒潮个例进行模拟,并将模拟结果与寒潮过境区六个验潮站增水情况进行对比,拟合结果良好。在此基础上,本文应用已构建的模式进行多组敏感性实验,探讨风暴潮增水与寒潮路径、寒潮强度的关系,总结寒潮风暴潮增水的时空变化特征。结果表明,风暴潮增水主要发生在垂直于风向的海岸线附近,且增水幅度和时间滞后情况与海底和大陆架的地形密切相关。寒潮引起的水位振荡峰值与风速之间存在正相关,水位振荡谷值与风速之间存在负相关,但水位振荡与风时之间不存在明显的相关性。此外,本文设计实验针对温带气旋对寒潮风暴潮增水的影响、天文潮与风暴潮的非线性相互作用进行研究,总结其在渤海及北黄海的独有特征。耦合型天气形势可根据寒潮路径和温带气旋的不同而分为横向冷锋引导、斜向冷锋引导和竖向冷锋引导的寒潮,其通常会产生更大幅度的风暴潮增水,且水位振荡呈多峰结构。天文潮与风暴潮间的非线性相互作用对风暴潮的大小和相位产生明显影响,不同阶段的天文潮产生的影响程度不同。

随后,本论文对中国近海北部寒潮风浪频谱和谱参量的成长特性进行了研究。基于第三代海浪模式SWAN,论文对寒潮浪的时空变化特征进行了分析,并输出海浪谱数据。可见,寒潮风浪频谱主要为单峰谱,可由Donelan谱较好的描述。海浪谱的成长可由三个相关性较强的特征参量(峰值频率、谱峰值和谱的零阶矩)的变化综合反映。此外,本文通过最小二乘法获得谱参量相对于三类通用的影响因子(风区、逆波龄和峰值频率)的成长关系,并对其进行系统对比。结果证明,风区和峰值频率用于描述谱参量较为合适,而逆波龄描述的成长关系在不同的海域存在差异。总的来说,本文所拟合出的成长关系更适用于中国近海北部寒潮风浪频谱的实际应用,改进了前人的结果。

最后,本文基于耦合系统COAWST构建中国近海寒潮影响下海洋动力灾害多致灾因子的耦合测报模式,确定适用的参数化方案和耦合方案。经验证,辐射应力方案和涡度力方案对不同风场、不同海域以及不同水位变化阶段影响不同,但总体说提高了风暴潮模拟的准确性。本文应用所建立的耦合模式开展了寒潮风暴潮与寒潮浪之间耦合作用机理研究,分析了它们之间非线性相互作用的特征及其对灾害过程的强化效应。结果表明,浪流相互作用主要影响近岸浅水区域和地形较复杂区域;浪致流效应对海表面应力、底应力均有影响,还诱生辐射应力或涡度力;流致浪效应对波高和波向的影响与水位和流场的性质有关。

总之,寒潮所引起的海洋动力过程灾害性不容小觑。本论文研究在极端天气条件下的风暴潮和海浪等现象的发生、发展规律及它们之间的共振或相互作用不仅在动力学上有重要的理论意义,而且对于改进风暴潮与海浪预报模式也有重要的实践意义。

其他摘要

Cold wave, including cold-air outbreaks, represents one of the most extreme meteorological systems. It is often accompanied by cooling, boosting and gale. The abruptness, long duration and strong directionality can often cause great disasters. The northern East China Sea, a semi-enclosed shallow body of water, is one of the most easily affected regions in the world. When a cold wave passes through the northern East China Sea, significant sea level rise and large waves are induced, which have a serious impact on human life and shipping and harm the economic development in coastal area of China. The dissertation intends to carry out systematic research on the dynamic mechanism and forecast method of the disastrous marine dynamic environments induced by cold waves in the northern East China Sea by a variety of means, such as observational data analysis, statistic analysis and numerical modeling.

Based on the NCEP Climate Forecast System Reanalysis data (from 2001 to 2010), the monthly distributions of invaded days and the spatiotemporal distributions of cold-wave wind direction and wind speed are shown. The northern East China Sea is affected by cold wave mainly from October to April and there is an obvious seasonal variation of cold-wave wind. Single weather systems occupy a bigger proportion. The main directions of cold-wave wind are from NE, NNE, N, NNW and NW. Occurrence probability and wind speed of cold-wave wind from generalized northeastern winds is bigger and higher than generalized northwestern winds.

A three-dimensional numerical model (ROMS) is developed to study storm surges induced by cold waves. Two cases are carried out to discuss the spatiotemporal variation of storm surges and test the reliability and accuracy of the model. In spite of errors from wind forcing, bathymetry and nonlinear interaction, the model outputs agree well with observations. The role of wind direction, wind speed, wind duration, extratropical cyclone and tide-surge interaction are investigated by conducting different sensitivity experiments. The results indicate that storm surges mainly happen at the coasts perpendicular to the wind directions. Surge range and time lag are related to the geometry of the basin and the continental shelf. The response of the sea-level fluctuations to cold wave indicates that there is a positive correlation between crests and wind speed, a negative correlation between troughs and wind speed, but no obvious correlations to wind duration. According to the relative positions and developmental stages of cold wave and extratropical cyclone, coupled weather cold wave can be classified into three types: cold wave led by zonal, NE-SW and meridional cold front. Coupled weather cold waves always yield a larger range and a multi-peak structure of surges. The tide-surge interaction has an obvious and different effect on the magnitudes and phases of storm surges for different tidal stages.

Besides, the growth of frequency spectra and spectral parameters of wind waves generated by cold waves in the northern East China Sea is studied. Based on a third-generation wave action model (the Simulating WAves Nearshore model), simulations are developed to analyze the spatiotemporal characteristics of wind waves and to output spectral data. It is shown that the single-peak spectra can be well described by the modified Joint North Sea Wave Project spectral form. The growth of wave spectra is comprehensively reflected by the evolution of the three characteristic parameters: peak frequency, spectral peak and wave energy, which have stronger correlation with one another than with wind field. Besides, the approximations of dependences between spectral parameters and the three types of universal induced factors are obtained with the least squares method and compared systematically. Fetch and peak frequency turn out to be suitable factors to describe the spectral parameters, while the dependences on the inverse wave age vary in different sea areas. In general, the derived relationships improve on results from previous studies for better practical application of the wind wave frequency spectrum in the northern East China Sea.

Finally, based on the coupling system COAWST, a coupled forecasting model of disastrous marine dynamic environments induced by cold waves is conducted. Suitable parameterization schemes and coupling schemes are confirmed. The radiation stress scheme and vortex force scheme both improve the accuracy of simulation by verification, but have different effects on different sea areas and different development stages. The characteristics and laws of the nonlinear interaction between the storm surges and waves induced by cold waves are further explored. The results indicate that the interaction mainly affect the shallow water area near the shore and area with rough terrain. Wave effects on current can not only influence the surface stress and the bottom stress, but also induce radiation stress or vortex force. Current effects on wave relate to the conditions of sea level and flow field.

In conclusion, the potentially catastrophic consequences of marine dynamics induced by cold waves should not be underestimated. The dissertation depicts the features, influencing factors, generative mechanisms, spatiotemporal variations and interaction between storm surges and waves, in detail. It is not only of great scientific significance in the research of ocean dynamics, but also of important practical importance to improve storm surge and wave forecasting models.

语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/154451
专题中国科学院海洋研究所
推荐引用方式
GB/T 7714
莫冬雪. 中国近海寒潮影响下的灾害性海洋动力环境研究[D]. 中国科学院海洋研究所. 中国科学院大学,2018.
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