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 (r 12) 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, r 0, is determined from r 12 using an outer wind structure model that assumes no deep convection beyond r 12. The global median values of r 12 and r 0 are 197 km and 423 km, respectively, with statistically significant variation across ocean basins. The global distribution of r 12 is found to be approximately log-normal, the distribution of r 0 is quantitatively much closer to log-normal, and the improvement in fit between r 12 and r 0 is attributed to the combined effect of the nature of the model employed and the paired distributions of r 12 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 r 12 and r 0 tend to expand very slowly with time early in the storm lifecycle and then becomes quasi-constant, though significant variance exists across storms. © 2010 by the American Geophysical Union.