Estimates of the bulk transfer coefficients and surface fluxes over the Tibetan Plateau using AWS data

A preliminary study is given on the bulk transfer coefficients and surface fluxes over the Tibetan Plateau, on the basis of data from four sets of AWS in Tibet from July 1993 to March 1999 according to P.R. China-Japan Cooper ation Research Project on Asian Monsoon Mechanism. The surface roughness le ngths are decided by the logarithmic wind law under neutral conditions usin g the least square method, the value at each station is scattered and seaso nal mean is obtained. The bulk transfer coefficients for momentum and heat are estimated using the flux-profile relationships, means of the bulk trans fer coefficients for momentum and heat are 4.44x10(-3)similar to4.75x10(-3) and 6.02x10(-3)similar to6.40x10(-3), respectively. The surface fluxes of momentum, sensible heat and latent heat are computed by bulk transfer formu lations, sum of sensible and latent heat at each station is about 100 W/m(2 ) In addition, diurnal and seasonal variations of the bulk transfer coeffic ients and surface fluxes as well as the relations among bulk transfer coeff icients, bulk Richardson number and surface wind speed are discussed in det ail using a composite method. A possible relationship between surface fluxe s and monsoon over the Tibetan Plateau is suggested, i.e., the surface heat transfer on the Eastern Tibetan Plateau is dominated by the sensible heat flux and latent heat flux jointly in the pre-monsoon and latent heat flux m ainly during the monsoon.