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 [ms superscript -1] wind (r12) [r subscript 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, r0 [r subscript 0], is determined from r12 [r subscript 12] using an outer wind structure model that assumes no deep convection beyond r12 [r subscript 12]. The global median values of r12 [r subscript 12] and r0 {r subscript 0] are 197 km and 423 km, respectively, with statistically significant variation across ocean basins. The global distribution of r12 [r subscript 12] is found to be approximately log-normal, the distribution of r0 [r subscript 0] is quantitatively much closer to log-normal, and the improvement in fit between r12 [r subscript 12] and r0 [r subscript 0] is attributed to the combined effect of the nature of the model employed and the paired distributions of r12 [r subscript 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 r12 [r subscript 12] and r0 [r subscript 0]tend to expand very slowly with time early in the storm lifecycle and then becomes quasi-constant, though significant variance exists across storms.