Evaluation of Tropical Cyclone Center Identification Methods in Numerical Models

Identifying the center of a tropical cyclone in a high-resolution model simulation has a number of operational and research applications, including constructing a track, calculating azimuthal means and perturbations, and diagnosing vortex tilt. This study evaluated several tropical cyclone center identification methods in a high-resolution Weather Research and Forecasting (WRF) Model simulation of a sheared, intensifying, asymmetric tropical cyclone. The simulated tropical cyclone (TC) contained downshear convective cells and a mesovortex embedded in a broader TC vortex, complicating the identification of the TC vortex center. It is shown that unlike other methods, the pressure centroid method consistently 1) placed the TO center within the region of weak storm-relative wind, 2) produced a smooth track, 3) yielded a vortex tilt that varied smoothly in magnitude and direction, and 4) was insensitive to changes in horizontal grid resolution. Based on these results, the authors recommend using the pressure centroid to define the TC center in high-resolution numerical models. The pressure centroid was calculated within a circular region representing the size of the TO inner core. To determine this area, the authors propose normalizing by the innermost radius at which the azimuthally averaged storm-relative tangential wind at 2-km height equals 80% of the maximum (R-80) at 2-km height. Although compositing studies have often normalized by the radius of maximum wind (RMW), R-80 proved less sensitive to slight changes in flat tangential wind profiles. This enables R-80 to be used as a normalization technique not only with intense TCs having peaked tangential wind profiles, but also with weaker TCs having flatter tangential wind profiles.