A new parametric tropical cyclone wind-profile model: Testing and verification

Over the years, a variety of parametric tropical cyclone radial pressure or wind profiles has been developed to depict a wind field within a tropical cyclone. Originally introduced to tropical meteorology by Depperman (1947), a Rankine (1882) vortex has been used in numerous studies to approximate the inner core of solid-body rotation of the tropical cyclone. Beyond the core radius, the tangential velocity decreases, with some values of about 1 . 0 6 . 0 ± being inversely proportional to radial distance from the rotation center. These velocity distributions were found to give a good approximation to the tangential wind profiles of tropical cyclones (Hughes 1952; Riehl 1954, 1963; Malkus and Riehl 1960; Gray and Shea 1973 among others). The Rankine model, however, does not seem to describe individual tropical cyclones well (Holland 1980). Other parametric pressureand/or wind-profile models have been formulated by Schloemer (1954), Holland (1980), Chan and Williams (1987), DeMaria et al. (1992), and Willoughby et al. (2006). The models, with the exception of the Willoughby et al. (2006) model, sometimes do not fit the observations of aircraft flightlevel tangential wind data, including the sharply peaked profiles of tangential winds in intense hurricanes. In their aircraft observational studies of tropical cyclones, Willoughby et al. (2006) not only modified the inner and outer tangential wind profiles of the Rankine model but as well eliminated the discontinuity at its radius by constructing a smooth, radially-varying polynomial ramp function in the annulus of tangential wind maximum. The Willoughby et al. model favorably compared with observed profiles of tangential wind. Holland (1980) formulated the most widely used parametric wind-profile model for such applications as storm-surge forecasting, windstorm underwriting, and tropical cyclone wind profiles. Willoughby and Rahn (2004), however, challenged the Holland profile that the areas of strong winds inside the eyewall and of nearly calm winds at the vortex center are unrealistically wide and that the winds outside the eyewall decay too rapidly with increasing radial distance from the center. Unfortunately, the profile can result in errors in the computation of a geopotential height or pressure. Wood and White (2010) formulated a new and different parametric vortex wind-profile model with appli___________________________ Corresponding author address: Vincent T. Wood, National Severe Storms Laboratory, 120 David L. Boren Blvd., Norman, OK 73072. E-mail: Vincent.Wood@noaa.gov cations to Doppler radar observations of dust devils, tornadoes, and thunderstorm mesocyclones. The model employs the five key parameters: maximum tangential wind ( x V ), radius ( x R ) at which x V occurs, curvature growth (κ ) that controls the inner velocity shape near the vortex center, decay (η ) that decreases the outer velocity profile outside x R with the radial distance from the vortex center, and radial width ( λ ) that controls a discontinuous or continuous tangential wind maximum at x R . The most important part of the model is that it