Air-sea Momentum Flux And The Analysis Of Turbulence Characteristics And Aerosol Optical Thickness

Marine atmospheric boundary layer turbulence characteristics and flux exchange between ocean and atmosphere are important for understanding the air-sea coupled model,ocean and atmosphere dynamic environment forecast and the impact on global climate change.Eddy correlation method obtains more and more attention in the air-sea interaction study as a direct means of observing atmospheric turbulence.Momentum flux and turbulence statistical characteristics of the air sea interface was researched using eddy correlation method based on the flux and wave measurements on Bohe measurement platform fixed on northern South China Sea during February 4 and March 12,2015.One hour as average time scale was determined by cumulative frequency curve.Temporal synchronization of waves and flux data sets was obtained by processing data based on average time scale.South China sea aerosol optical thickness was analyzed based on the marine optical thickness data provided by the National Oceanic and Atmospheric Administration during February 1 and March 14,2015.It was found that:In most time of the whole observation period,northeast moderate easterly winds,wave height less than 1 m significant,peak period between 5 and 10 s,peak wavelength less than100 m and southeast swells affected by northwest islands are found.Atmospheric stability varies mainly between-1 and 1,major in stable stratification.The average turbulence intensity of the longitudinal,lateral and vertical velocity components is 0.0911,0.0863 and0.0392,respectively.The northern South China Sea have the biggest aerosol optical thickness beyond 0.6,especially the Beibu Gulf,on average at 0.4,far away from the land area have aerosol optical thickness less than 0.2.The wind stress vector depends on not only the sea surface winds,but also on the surface waves and atmospheric stratification.The wind stress vector is to the left of the local wind and the deviation angle may be very big,sometimes may be 80^o and may still exist when wind speed is large for stable stratification case.The wind stress component of in the traditional rectangular coordinate system and the wind-wave coordinate system is more convergent for neutral and stable stratification cases than unstable stratification case.The longitudinal stress component?_x in the traditional rectangular coordinate system and aligned with wind?₁ in the wind-wave coordinate system increase non-linear with velocity and quasi-linear with inverse wave age.The greatest contribution to the wind stress is longitudinal stress component?_x,but wind stress vector deviate from the wind direction due to the non-zero of the lateral stress component?_y.The maximum value of the drag coefficient occur in the 2 m/s wind speed,most values?about 97%of the data?are between 0.5 and 2.5×10^-3 for the stable stratification case and good agreement with actual situation.It is found that the OO02 scheme considering the wavelength and wave age is the best by comparing three different roughness scheme in COARE 3.0.