Research On The Wave Pattern Induced By A Moving Atmospheric Pressure Disturbance

Meteorological tsunami(also referred as meteotsunami)is one type of sea surface fluctuation with the same frequency band as typical tsunami waves,which is generally caused by the rapid movement of atmospheric pressure disturbances.Forced waves are amplified by a variety of resonance mechanisms and evolve into significant,even devastating,sea level oscillations at coastal areas.Because of the complex mechanisms,it is difficult to forecast the meteorological tsunami.The purpose of this study is to investigate the wave pattern and development mechanism of forced wave induced by atmospheric pressure disturbances,as well as the evolution process when disturbances move near shore,which is intended to find out the key factors that lead to disastrous meteorological tsunami waves.Based on the nonlinear shallow water equation,a numerical model of ocean hydrodynamics is established,and the waves induced by moving pressure disturbance are analyzed in detail.Different atmospheric pressure disturbances moving above the sea generate different wave patterns,which can be determined by Froude number Fr.In general,Fr=1 is considered as a critical value,and the well-known Proudman resonance occurs when Fr=1,resulting in significant waves.In this study,the wave pattern induced by moving atmospheric disturbance is simulated in unbounded flat-bottom water area,and the development mechanism of the forced wave are analyzed based on energy equation.The results show that the pressure gradient,the difference between the velocity of pressure movement and the velocity of shallow water wave are the main factors affecting the process of wave development.The movement of atmospheric pressure disturbance near the coast would probably cause tremendous fluctuations near shore,which poses great threat to the safety of coastal areas.In this study,the forced wave induced by an atmospheric pressure disturbance moving over a constant slope from deep sea to shore is numerically investigated.The wave pattern evolves from a concentric-circle type into a triangular type with the increase of the Froude number,which accords with the analysis in the unbounded flat-bottom area.However,a hysteresis effect has been observed in wave pattern evolution and the presence of wave peak,which implies the maximum amplification of the forced wave induced by pressure disturbance cannot be simply predicted by Fr=1 under Proudman resonance theory.The effects of the atmospheric pressure disturbances and slope have been discussed.The results show that a significant wave peak can be generated by a pressure disturbance with small spatial scale and rapid motion over a milder slope.An extremely high water run-up occurs when the forced wave hits the shore,which is also an essential threat to coastal security.The results also show that the maximum run-up is greater in higher pressure amplitudes and steeper slopes,but it's not monotonously varying with the increase of disturbance moving speed and spatial scale.There exists a most dangerous medium-sized speed and scale which may cause disastrous nearshore surge.What's more,the phenomenon of edge wave is also studied,which is generated by the atmospheric disturbance moving along the shore.Based on the theory of Greenspan and a set of numerical experiments,the effects of the disturbances and topography on the wave generation,evolution and maximum wave amplitude are systematically studied.The results show that edge waves will be excited when the velocity of atmospheric disturbance is greater than the critical velocity,and significant wave will be generated under a medium-sized disturbance on a medium slope.In addition,it takes approximately 4 to 5 wave periods for the edge wave to become significant.