Based on turbulence measurements from sonic anemometers instrumented at multiple levels on a 356 m-tall meteorological tower located on the south coast of China, an observation study of the turbulence dissipation rate (ϵ) in a landfalling tropical cyclone boundary layer (TCBL) is conducted. Three indirect methods (i.e., the power spectra, the 2^nd- and the 3^rd-order structure functions) are compared for the calculation of ϵ. The 3^rd-order structure function gives the smallest ϵ among the 3 methods with the widest spread for uncertainty. The 2^nd-order structure function gives similar ϵ estimates as the power spectra, and is adopted for its reduced uncertainty. The measured ϵ in the landfalling TCBL is of O(10^-1) m² s^-3, much greater than typical atmospheric boundary layer values as well as oceanic TCBL values. ϵ is found to scale with the local friction velocity rather than the surface friction velocity, implying a highly localized nature of turbulence. Conventional parameterizations of ϵ are evaluated against observations. Process-based ϵ models assuming a local balance between shear production and dissipation prove inadequate, as shear production merely accounts for half of the dissipation away from the surface. In comparison, scaling-based ϵ models used by planetary boundary layer (PBL) schemes are more advantageous. With some tuning, the performance of an ϵ model in a widely used PBL scheme is shown to produce similar values to observations.
 

Tropical Cyclone；,boundary layer,observation