A SAR-Based Parametric Model for Tropical Cyclone Tangential Wind Speed Estimation

The tangential wind speed increases from the center to the eyewall of tropical cyclones (TC) along the radial direction and begins to decay when it extends outward. The tangential wind profile model is one of the most effective and widely used methods to reconstruct the TC radial wind speed. This article proposes a parametric tangential wind profile (TWP) model based on high-spatial-resolution synthetic aperture radar (SAR) imagery. The new model functions are piecewise with maximum tangential wind speed as a threshold, and all of them are designed as nonlinear. Notably, the derivative at the segmentation threshold is zero to ensure a smooth transition of the estimated wind speed profile. With the SAR-derived azimuth-averaged wind speed, we can determine the model parameters and get the tangential wind speed. The TWP model outperforms the commonly used single-modified Rankine vortex (SMRV) model, as it better resolves the tangential wind profile shape as depicted by both SAR-derived winds and hurricane hunter stepped-frequency microwave radiometer derived winds. A comprehensive analysis of the TWP model parameters is carried out by fitting tangential winds for 620 hurricane hunter flights. Interestingly, the tangential wind profiles for major hurricanes show a similar shape. The proposed TWP model can be used for improved TC characterization and forecasting purposes.