A discussion on influences of turbulent diffusivity and surface drag parameterizations using a linear model of the tropical cyclone boundary layer wind field

摘要

In order to investigate and predict dynamics and developments of the tropical cyclone boundary layer (TCBL), theoretical and engineering models depicting the TCBL wind field are of great academic and practical interest. In the present study, a linear height-resolving model, where the vertically varying turbulent diffusivity (K) and speed dependent surface drag coefficient (C-d) parameterizations are incorporated, is proposed based on the original model proposed by Kepert (2001 The proposed model is validated through comparisons with the estimates made based on the observational data gathered by dropsondes. As the more realistic and sophisticated parameterizations are integrated, the proposed model produces predictions in better agreements with observations in the lower part of the TCBL. It is noted that the value of the proposed model is not only the improvements over the original model by Kepert (2001). but also the room for more sophisticated K and C-d parameterizations. With the help of the proposed model, it is feasible to discern the fundamental relationships between K and C-d parameterizations and the TCBL wind field in a parametric study. As the first step, a few K and C-d parameterizations are implemented in the proposed model, and their influences on the prediction of the TCBL wind field are systematically discussed. It is concluded that, whereas the prediction of the TCBL wind field is sensitive to the parameterization of K, C-d has limited effects on the prediction. Moreover, assuming K and C-d as constants could lead to erroneous estimates of the wind profile and strength of surface winds in the TCBL.