A Semi-theoretical Model Of The Tropical Cyclone Boundary Layer Wind Field And Its Application In Sea-land Transition

As the medium between the sea surface and the upper atmosphere in a tropical cylone,the tropical cyclone boundary layer(TCBL)plays a crucial role in the overall dynamics of the Tropical Cyclone.Specifically,the turbulence exchanges within the TCBL determine the supply of thermal energy and the transportation of momentum in the Tropial Cyclone system.The TCBL concens the human life as it hosts most of the manmade structures and facilities.When moving towards the coast,Tropical Cyclones bring strong surface winds,heavy rains and sometimes storm surges,which consequently cause infrasture damages,property losses,and even casualties.Hence,a thorough investigation on the TCBL is of great practical and academic interests.Given the abrupt change between the onshore and offshore underlying terrains,there is a land-sea transition in the TCBL wind field when it is approaching the coast or making a landfall.Although the investigations on the prediction of Tropical Cyclone intensity,storm surges and Tropical Cyclone induced damages have been growing in numbers,works on the sea-land trasition of the TCBL are relatively rare.In the current study,the sea-land transition is comprehensively investigated based on a proposed semi-theoretical model.This study contains four major parts.Firstly,an improved linear height-resolving model is proposed on the basis of the original model by Kepert,in which the spatially varying turbulent diffusivity and speed dependent surface drag coefficient are incorporated.The improved model is validated through comparisons with observational data gathered from typhoon/hurricane reconnaissance projects.In addition,the influence of parameterization schemes on simulating wind filed is systematically investigated based on the improved model.It is expected that as more realistic and sophisticated turbulent models are integrated,the improved model may outperform the original Kepert model.Secondly,two other widely accepted semitheoretical models,including the analytical model proposed by Kepert and the similarity model by Foster,are reviewed systematically in the present study.Utilizing a set of archived over ocean surface wind field information provided by the H*wind database,rigorous comparisons among the three models are performed to examine their capability for accurately and realistically estimating the intensity,inflow angle,asymmetric characteristics and spatial distribution of the TC surface wind field.Thirdly,the tangential component of the momentum budget equation is considered.A physical mechanism accounting for the difference between the TCBL wind speed profile and the classic logarithmic profile is proposed.The improved model is utilized to simulate several TC cases and spatial variation of the deviations,and the factors influencing the deviations are discussed based on the simulation results.Fourthly,a theoretical model illustrating the land-sea transition of TCBL wind field is proposed,where the improved model is utilized to determine the starting and eventual profiles above the sear surface and the land.The widely accepted internal boundary layer model is used,in addition to the improved model,to illustrate the transition process.