极端海洋事件严重威胁着海岸带地区生命财产和基础设施安全，认识极端海洋事件的致灾机理能够为海岸带防灾减灾和建设规划工作提供科学参考依据。本文聚焦极端海洋事件致灾问题，探究水下火山喷发、走滑断层地震等非传统因素引发海啸的机理，并分析海啸诱发港湾共振的过程和共振对海啸的增强作用；剖析热带气旋诱发海表近惯性流动共振增强的条件，并深入探究近岸地区近惯性流动的发展、消退规律，丰富和完善了关于极端海洋事件致灾机理的理论认识。 本文揭示了水下火山喷发引发长波海啸，并诱发环太平洋带港湾共振的机理。火山口处水深浅、火山喷发时间长、喷出物体积多的水下火山喷发能够诱发波幅较大的长波海啸并跨洋传播。以2022年汤加HT-HH火山海啸事件为例，基于ROMS海洋模式模拟火山喷发过程引发海啸的波形、波幅及抵达时间等特征，相比已有研究更精准地再现了海啸波幅及抵达时间。通过谱分析方法得到火山海啸波波谱，指出火山海啸波的特定波段可与环太平洋带不同的港湾形成共振。 本文阐明了走滑断层地震通过晃荡作用引发海啸，并诱发港湾共振的机理。以2018年印度尼西亚Palu湾地震海啸事件为例，考虑走滑断层地震产生的晃荡作用，基于ROMS海洋模式对该事件中海啸的波形、抵达时间以及淹没水深进行了模拟，与实测值吻合良好。通过谱分析及小波分析方法进一步指出，走滑断层地震产生的水平加速度可通过晃荡作用在附近港湾中激发不同周期的海啸波，其中特定波段与港湾的共振周期接近，诱发了港湾共振，致使海啸放大增强。 本文分析了热带气旋作用下近惯性流动的产生和消退的物理过 程及关键影响因素。基于理想风场，通过参数分析方法明确了热带气旋在海表诱发近惯性流动共振增强受热带气旋中心移动速度、距热带气旋路径距离的影响。以2011年飓风Irene事件为例，通过ROMS海洋模式模拟了其在中大西洋湾中所引发的近惯性流动分布特征，并与实测值吻合良好。通过能量平衡分析方法，剖析了热带气旋诱发的近惯性流动在港湾中的消退机理：在深海区域，近惯性流动消退主要受到垂向紊流耗散及垂向能量传递作用影响；而在近海区域，近惯性流动消退主要受到垂向紊流耗散及海底摩擦作用影响。垂向紊流耗散是引起近惯性流动消退的重要因素，其强度受海洋垂向剪切强度控制。
The extreme ocean events severely threaten human lives, properties and infrastructure in the coastal zone. Understandings of the extreme ocean events would guide the coastal disaster prevention and construction planning. This thesis focuses on the physical mechanisms of extreme ocean disasters. Firstly, the role of the non-traditional factors, such as the underwater volcanic eruption and the strike-slip fault earthquake, in the tsunami generation is explored. The process of harbor resonance agitation by the tsunami is also analyzed. Secondly, the critical factors affecting the resonance between the tropical cyclone (TC) and the near inertial currents induced by TC at sea surface are pointed out. Moreover, the development and decay mechanism of the near inertial currents is clarified. It is demonstrated that the underwater volcano eruption with a shallow crater depth, a long eruption duration and a large ejected volume, could effectively generates a long-wave tsunami, which is capable of propagating across the ocean. The 2022 Tonga Honga Tonga-Hunga Ha’apai volcanic tsunami is simulated by the Regional Ocean Modeling System (ROMS). Numerical results, including the amplitude and the arrival time of the tsunami, are shown to agree better with the field data than previous studies. Based on the spectral analysis, it is found that the volcanic tsunami waves show wider period bands, which can match a wide range of natural periods of normal size harbors in the Pacific Rim. It is shown that the sloshing effect induced by the strike-slip earthquake could dominate a tsunami event if it occurs in a semi-closed water body near the epicenter and the ground motion triggered by the earthquake is strong enough in the horizontal directions. The 2018 Palu Bay seismogenic tsunami is simulated by the ROMS model. Numerical results, including the waveform, the arrival time and the inundation of the tsunami, are shown to agree well with the field data. Based on the wavelet analysis, it is found that the sloshing induced tsunami waves actually contain a spectrum of multiple wavelengths. When the specific period of the tsunami is close to the natural period of the harbor, the harbor resonance could be agitated and the tsunami wave could be further amplified. The development and decay mechanism of the near inertial currents induced by the TC is clarified. It is pointed out that the resonance between the surface near inertial currents and the rotating wind stress of TC, which could largely enhance the near inertial velocities, is mainly influenced by the translation speed of TC and the distance from the TC track, based on the sensitivity analysis. The strong near inertial currents in Mid-Atlantic Bight of the US East Coast induced by Hurricane Irene in 2011 are simulated by the ROMS model. Numerical results obtained with the ROMS model are shown to agree well with the field data. Based on the energy budget, it is clarified that in the deep water region, near inertial energy is basically balanced by the vertical turbulence diffusion and downward divergence, while in the continental shelf region, near inertial energy is mainly dissipated by the vertical turbulence diffusion and partially by the bottom friction. Local dissipation of the near inertial kinetic energy due to turbulence diffusion is closely related to the rate of the vertical shear.
