Structure of Boundary Layer Wind and Turbulence in Super Typhoon Ragasa and Typhoon Wipha During Landfall

Abstract

Boundary layer turbulence and vertical mixing exert great control over the structure and evolution of tropical cyclones (TCs). However, scaling and parameterizing them remains challenging due to their inherent complexity and limited observations. Based on a 356‐m‐tall meteorological tower and wind profilers at three sites, this study analyzes the structure of wind and turbulence in the boundary layer of Super Typhoon Ragasa and Typhoon Wipha during landfall. Wind profile observations suggest an asymmetric structure with more significant inflow in the right‐front quadrant than right‐rear. Local scaling works for describing the dimensionless wind velocity variances and turbulent kinetic energy but is subject to a high degree of uncertainty. Friction velocity‐based non‐local parameterization performs better than wind velocity variance‐based local schemes in reproducing the observed vertical eddy diffusivity for momentum, while the larger‐than‐unity scaling parameter in the commonly used K‐profile parameterization scheme indicates higher‐than‐parameterized vertical turbulent mixing. These observational results suggest that directly applying similarity laws and parameterization schemes developed for homogeneous, straight‐line winds to landfalling TCs may introduce significant uncertainties. Accounting for the influences from the inhomogeneous features, such as rolls, mesoscale vortices, and underlying surface heterogeneity, may represent a future direction of improvement.