AN ANALYTICAL MODEL FOR SIMULATION OF THE WIND-FIELD IN A TYPHOON BOUNDARY-LAYER

An analytical model has been developed for calculating the wind field in a moving typhoon boundary layer. The present model has an upper inviscid layer of cyclostrophic balance and a lower friction layer controlled by a surface drag coefficient and eddy viscosity, Velocity in the inviscid region is described first, using the assumption that the wind field moves with the translation velocity of the typhoon. Perturbation analysis is then performed to obtain the tangential and radial boundary layer velocity in the friction region. Wind speeds and directions predicted by the present model agree favorably with observations obtained at a 100 m height tower during three typhoons in 1991. Rapid variations in wind speed due to surface roughness and topography around the tower are also amply demonstrated. In the final section of this paper, a case study is presented to examine the wind field associated with a typhoon, as well as the characteristics of the ratio of surface to gradient wind speeds G(r) and the inflow angle y. The results indicate that previous observation data obtained at coastal areas during typhoons can be explained satisfactorily by this model.