A QuikSCAT climatology of tropical cyclone size

Abstract

QuikSCAT data of near‐surface wind vectors for the years 1999–2008 are used to create a climatology of tropical cyclone (TC) size, defined as the radius of vanishing winds. The azimuthally‐averaged radius of 12 ms−1 wind (r12) is calculated for a subset of TCs (N = 2154) whose centers of circulation were clearly identifiable via subjective analysis of the QuikSCAT‐analyzed wind field. The outer radius, r0, is determined from r12 using an outer wind structure model that assumes no deep convection beyond r12. The global median values of r12 and r0 are 197 km and 423 km, respectively, with statistically significant variation across ocean basins. The global distribution of r12 is found to be approximately log‐normal, the distribution of r0 is quantitatively much closer to log‐normal, and the improvement in fit between r12 and r0 is attributed to the combined effect of the nature of the model employed and the paired distributions of r12 and f. Moreover, the normalization employed by Dean et al. (2009) is found to weaken rather than improve the log‐normal fit. Finally, within a given storm, both r12 and r0 tend to expand very slowly with time early in the storm lifecycle and then becomes quasi‐constant, though significant variance exists across storms.