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

Abstract

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 Cooperation Research Project on Asian Monsoon Mechanism. The surface roughness lengths are decided by the logarithmic wind law under neutral conditions using the least square method, the value at each station is scattered and seasonal mean is obtained. The bulk transfer coefficients for momentum and heat are estimated using the flux-profile relationships, means of the bulk transfer coefficients for momentum and heat are 4.44×10-3∼4.75×10-3 and 6.02×10-3∼6.40×10-3, respectively. The surface fluxes of momentum, sensible heat and latent heat are computed by bulk transfer formulations, sum of sensible and latent heat at each station is about 100 W/m2. In addition, diurnal and seasonal variations of the bulk transfer coefficients and surface fluxes as well as the relations among bulk transfer coefficients, bulk Richardson number and surface wind speed are discussed in detail using a composite method. A possible relationship between surface fluxes 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 mainly during the monsoon. ©2001, Meteorological Society of Japan.