| The air-sea interaction between tropical cyclones(TCs)and the Kuroshio in the East China Sea(ECS)is an important topic in the study of air-sea interaction.It is one of the important scientific issues of great interest to coastal communities in eastern Asia,which greatly influences the weather variation in the offshore area of China.In this thesis,the effects of the Kuroshio on the development of different TCs and the responses of the Kuroshio to different stages of TCs are discussed from the perspective of the air-sea interaction by developing an improved regional coupled model,and using the statistical,diagnosic,and full dynamic budget analyses.A regional coupled model is developed,and adapted for the simulation of the Kuroshio and TCs in the ECS.Sensitivity tests of parameterization schemes for the air-sea coupled model is first conducted.Solution sensitivity to factors such as the intensity of the Kuroshio,TC features,waves and sea sprays which are calculated by the sea spray generating function containing various particle radii,are included in the calculation.It is demonstrated that the improved model can better simulate the TC features,the momentum flux and sensible heat flux at the air-sea interface under TC conditions.To investigate the influence of the Kuroshio on the evolution of TCs,by using the improved regional coupled model,this thesis systematically analyzies three groups of TCs(intensifying,weakening and abnormal TCs)and reveals that the Kuroshio effects on TCs is through a forcing mechanism,under the conditions for the Kuroshio to most effectively strengthen a TC(with moving speed 6+1.5m/s and the mean distance from the Kuroshio is25+15km).The forcing mechanism with the turbulent heat flux in the vertical section triggered by the convection instability,is made up of(1)the local convection burst triggered by the Kuroshio,(2)the vertical mixing channels conveying heat and water vapor upward in the thermodynamic and dynamic boundary layers,and(3)the radial outflow and deep convection at a height of more than 4 km.In the intensification stage of the forcing mechanism,the convective burst is stable,and this mechanism can effectively strengthen the TC.However,as the TC continues to intensify,the mechanism moves into a stagnating stage,the effect of the TC-drived cold wake becomes important and the convective burst disappears at the air-sea interface.By comparing the different stages of the various cases,it is found that(1)the Kuroshio is the trigger and energy source of this mechanism,and determines whether the mechanism occurs or not.The intensity and persistence of the mechanism are determined by the TC characteristics,such as intensity and translational speed,as well as the ocean responses.(2)The impact of the Kuroshio on TC is not linearly related to the TC intensity.The Kuroshio most effectively strengthens a TC,when the TC intensity and the translational speed are both moderate.Those conditions are favorable for the mechanism to sustain a longer time.In contrast,the intensification efficiency of fast-moving TC with strong intensity,or those with abnormal path is weak.For those TCs,the air-sea difference becomes smaller,the convection burst disappears,and the mechanism stops quickly.Using a series of the solution from the improved regional coupled model and the full dynamic budget analysis,this thesis quantitatively analyzes three groups of TCs(enhanced,weakened and abnormal TCs)to explore the responses of the Kuroshio to the TC’s development and their feedbacks.The analysis reveals that the responses in the upper ocean in the Kuroshio are separated into the three vertical levels and the responses at different levels are produced at the different stage of the mechanism.It is found that(1)in the intensification case,the cooling occurs at the sea surface where the wind speed is maximum and the convection burst.The subsurface warming also occurs at this stage.The surface cooling and the subsurface warming are caused by the wind-induced mixing term(69 %),the pressure gradient term(30%),and the advection term(1%).In the stagnation stage,the cooling begins to recover,but the subsurface warming continues to expands.Below the subsurface warming layer,the altemating bands of cold and warm water appear.The proportions of the three processes change to 29%,69% and2%,respectively.(2)In the weakening case,the strong surface cooling occurs,and the subsurface warming occurs in the strengthening stage.The proportions of the three processes change to 86%,0.3% and 13.7%,respectively.In the stagnation stage,the cooling still exists and subsurface warming gradually decreases.The proportions of the three processes change to4%,85% and 11%,respectively.(3)In the abnomal path case,it is found that before the path rotation,the response is mainly caused by wind-induced mixing(84 %).During and after the path rotation,the contribution of pressure gradient force and wind-induced mixing are comparable.Due to the relative change of the wind directions and the Kuroshio,the vetical mixing is produced by the relative movement between the flow field driven by the pressure gradient and the Ekman flow during the path rotation.After the path rotation,the vetical mixing is produced by the relative movement between the inertial current and the Ekman flow.By comparing the response processes in the different cases,it is found that the major contributors are different and the turning point is the time when the convective burst disappears at the airsea interface.The main conclusion of the thesis is that effects of the Kuroshio on TCs and the response of TCs to the Kuroshio are mutually driven and influenced by the convection burst at the airsea interface,which constitutes a relatively complete air-sea interaction process between TCs and the Kuroshio in the ECS. |
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