Study On Disastrous Ocean Dynamical Environment Under The Influence Of Cold Waves In The Northern East China Sea

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 coldwave 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 thirdgeneration 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.