A New Asymmetric Parametric Tropical Cyclone Surface Wind Field Model

In the field of catastrophe modeling, knowledge of the structure of a Tropical Cyclone (TC) surface wind field is imperative for accurate risk assessment. For computational efficiency, TC wind fields are often estimated using a parametric model, where the full 2-D wind field is described by a few parameters, such as maximum wind speed and radius of maximum winds. Most parametric models currently used to estimate risk assume an axisymmetric vortex with an additional asymmetric component due only to storm motion. Recent studies have demonstrated that the low-wavenumber asymmetric TC wind field in an evolving vertically-sheared environment is more complex. Here we introduce a new parametric TC model whose wavenumber-1 asymmetry depends on the combined impacts of both storm motion and environmental shear. This proposed model azimuthally expands the Willoughby et al. (2006) dual-exponential TC radial profile of wind speed by introducing an asymmetric structure. The model is developed from nearly twenty years of Stepped-Frequency Microwave Radiometer surface wind speed data acquired on over 550 flights in Atlantic and North Pacific TCs . In this talk, the methodology of the new asymmetric parametric model will be discussed and examples of the impact of asymmetry on wind field structures will be given.