Tropical cyclone wind field asymmetry-Development and evaluation of a new parametric model

A new parametric model is developed to describe the wind field asymmetry commonly observed in tropical cyclones or hurricanes in a reference frame fixed at its center. Observations from 21 hurricanes from the North Atlantic basin and TC Roger (1993) in the Coral Sea are analyzed to determine the azimuthal and radial asymmetry typical in these mesoscale systems after removing the forward speed. On the basis of the observations, a new asymmetric directional wind model is proposed which adjusts the widely used Holland (1980) axisymmetric wind model to account for the action of blocking high-pressure systems, boundary layer friction, and forward speed. The model is tested against the observations and demonstrated to capture the physical features of asymmetric cyclones and provides a better fit to observed winds than the Holland model. Optimum values and distributions of the model parameters are derived for use in statistical modeling. Finally, the model is used to investigate the asymmetric character of TC systems, including the azimuth of the maximum wind speed, the degree of asymmetry, and the relationship between asymmetry and forward speed.