Observations of Boundary Layer Wind and Turbulence of a Landfalling Tropical Cyclone

Abstract

This study analyzed the atmospheric boundary layer characteristics based on the multiple level observations by a 350-m height tower during the landfall of Super Typhoon Mangkhut (1822). Mean wind profiles showed logarithmic wind profiles at different wind speed ranges suggesting nearly constant flux layers. The height of the constant layer increased with the wind speed and deceased with the radial distance from the storm centre. This behaviour was supported by flux observations. Momentum fluxes and turbulent kinetic energy increased with the wind speed at all flux measurement levels. The drag coefficient (surface roughness) estimated was nearly a constant with a value of 8´10-3 (0.09 m). Both the estimated eddy diffusivity and mixing length varied with height. The eddy diffusivity also varied with the wind speed. Our results supported that the eddy diffusivity is larger over land than over ocean in a same wind speed range.