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.