Observational Study Of Turbulent Fluxes' Characteristics In Western North Pacific Typhoons

We mainly use dropsonde and high-frequency data of tower to study the turbulent fluxes and their exchange coefficients of typhoons over the Western Pacific Ocean.The study of typhoons over the Western Pacific Ocean is divided into two areas:offshore and open sea.We compare CD and CK between typhoons and hurricanes,and explores the causes for different magnitude of CD using Global Positioning System?GPS?dropsonde combined with NOAA 0.25° SST data in open sea area.In the offshore area,10Hz high-frequency and SST data from the tower of the Bohe Ocean Platform Tower are used to analyze the characteristics of turbulent fluxes and flux exchange coefficients with wind speed at 10 m attitude(U₁₀)in landfall typhoons,as well as factors affecting the characteristics of fluxes.The main conclusions are as follows:The magnitude of CD in typhoons and hurricanes over the open sea is proportional to wind speed at low wind speed(U₁₀<25 m s-1),and reaches saturation in the range of 25 m s-1<Ujo<30 m s-1.After U₁₀ exceeds 30 m s-1,CD continues to increase with wind speed until saturates again around 40 m s-1,and then CD decreases with wind speed;CK slowly increases with wind when U₁₀<45 m s-1.The value of CK/CD in hurricanes is positively correlated with wind speed.In general,the size of CD,CK,and CK/CD are significantly correlated with 10 m attitude's wind speed in tropical cyclones.The magnitude of CD in typhoons is larger than that in hurricanes at a given wind speed,especially at higher wind speeds(U₁₀>30 m s-1),while the magnitude of CK in typhoons and hurricanes are closer.Through sensitivity test analysis,we find that the difference in CD between the two basins is related to internal and environmental differences of typhoons and hurricanes.The intensity of typhoons and the distance between observation site and the center of typhoons influence the magnitude of turbulence fluxes in offshore area.The greater the intensity of the landing typhoons,the faster the momentum flux increases with the wind speed.The closer the observation point is to the typhoon center,the faster the heat flux will grow.The magnitude of each flux exchange coefficients is inversely proportional to the wind speed when U₁₀<5 m s-1.After U₁₀ exceeds 5 m s-1,CD increases with wind speed and this is consistent with observations in the Atlantic offshore area.While CK,CH and CE remain almost unchanged in the range of 5 m s-1?U₁₀?18 m s-1.When U₁₀?18 m s-1 the magnitude of CK in offshore typhoons is similar with that over open sea,but it is smaller than the high-frequency observations in the Atlantic Ocean.After U₁₀ exceeds 18 m s-1,the magnitude of CK in the high-frequency observations over Atlantic is close to our results obtained by dropsondes.