Statistical Analysis Of The Impact Of Typhoons On Cyclonic Eddies And Study On The Influence Of Cyclonic Eddies On The Upper Ocean Responses

The western North Pacific is a region which is influenced by monsoon,complicated hydrological condition and terrain.It becomes a place where both warm and cold eddies are frequently observed throughout the year,and also intense tropical cyclones occur most frequently in the world.The existing literatures find that COEs may be influenced by typhoons in various ways.The preexisting cyclonic ocean circulation may influence the magnitude and the location of SST cooling which will cut down the water and heat flux to typhoon's enhancement.And also the COEs may be intensified under appropriate conditions after the passage of a typhoon,which will also influence the responses of the upper ocean.The temperature response is different between inside and outside the COEs.Above all,there has been little investigation into the underlining physical processes of typhoon's impact on COEs.In this paper,we explored the response of COEs by using satellite remote sensing data and model.Firstly,based on the daily sea level anomaly(SLA)data from 2000 to 2014,a modified eddy detection was used to systematically analyze the statistical characteristics of eddies under the influence of typhoons in this period.Although there were 85 super typhoons passing over a huge number of COEs,only 32 COEs were significantly impacted by 28 super typhoons.This paper also primarily investigated the activities including geometric and physical parameters such as the area,SST,SSHA,tropical cyclone heat content(TCHP)and eddy kinetic energy(EKE)of COEs influenced by super typhoons.Then,the responses of COEs to typhoons were studied by analyzing the correlation of these changes of parameters and the properties of typhoons like intensity,translation speed,and forcing time.The results showed that the changes of COEs were most sensitive to the forcing time.The pre-existing COEs also played a significant role in determining the strength and location of large SST cooling.Secondly,a mesoscale model coupling the Weather Research and Forecasting model with 1-D ocean mixed layer model and the three-dimensional Price-Weller-Pinkel ocean model was used to investigate the dynamical ocean response to Sepat(2007).The C3D included horizontal advection,vertical advection and vertical mixing process could better capture the upper ocean response than C1D,namely,SST cooling.This negative SST feedback cut down the water and heat flux to the intensification of typhoon,which reduced the precipitation in Taiwan at last.And the height of the boundary layer also had a close connection to SST cooling too.Thirdly,the upper ocean had significant responses under the influence of Sepat.There existed strong near-inertial currents which was in opposite phases in the surface mixed layer and in the thermocline.It was dominated by excitation of the first baroclinic mode.And the thermohaline responses showed temperature and salinity responses had a three-layer vertical structure,which was characterized by the cooler and saltier water in the surface layer,the warmer and fresher in the subsurface layer,and the cooler and saltier in the deeper layer.These responses were much stronger to the right of the typhoon track in the surface and subsurface layers.Based on the model output analysis,we found that the surface cooling was induced by vertical mixing,subsurface warming and cooling were related closely to vertical mixing and upwelling and upwelling was responsible for the cooling below the subsurface.At the same time,the pre-existing cyclonic eddy at the left side of the typhoon track became stronger with the increasement of vorticity and kinetic energy.The velocity decayed slower in eddy's mixed layer,which meant there was much kinetic energy available to increase vertical shears for entrainment cooling.These led to striking cooling in the surface layer and warming in the subsurface layer.And the stronger upwelling in the water column also responsible for much cooling in the subsurface layer.The warming and cooling responsese in the subsurface layer were much stronger than outside the eddy.