The Internal Boundary Layer of Tropical Cyclone

Abstract

In this study, a series of large-eddy simulation experiments are carried out to investigate the internal boundary layer of tropical cyclones, the structure of which often changes when a tropical cyclone make landfall, under various circumstances, including different storm intensity and radius, as well as distinct surface types and roughness. Large-eddy simulations driven by tropical cyclone-like winds are first performed over homogeneous surfaces, either over parameterized ocean surfaces or land surfaces of fixed roughness lengths. By comparing with the simulations then carried out over a straight coastline, where flows experience a step change of roughness, mimicking onshore and offshore cases, the characteristics of the tropical cyclone internal boundary layer are highlighted. Instead of just focusing on the horizontal mean vertical profiles, comprehensive analyses have been done to explore the spatial structure, temporal evolution and the budget of turbulent kinetic energy, within this unique type of boundary layer. In particular, the rotation rate and wind speed of a storm, as well as surface drag, are found to have signification impact on the orientation and strength of coherent structures. In onshore cases, coherent structures contain more energy and supergradient jets are weaker and shallower downstream of a coastline, relative to homogeneous surface cases, and vice versa for offshore cases. Finally, while it is still in a testing process, a framework that modifies traditional numerics of large-eddy simulation models particularly for simulating a large horizontal extent of a tropical cyclone using limited computing resources is proposed. The challenges encountered during the development process are documented.

Date of Award	1 Mar 2018
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Chung Leung Johnny CHAN (Supervisor)