Limited Width of Tropical Cyclone-Induced Baroclinic Geostrophic Response

Despite the large radius (R-17) of gale-force wind of a tropical cyclone (TC), the observed TC-induced effects on mesoscale and large-scale ocean via the baroclinic geostrophic response are found to have a limited cross-track width; this strange but important phenomenon is interpreted here. Driven by the wind stress curl (WSC), the TC-induced geostrophic response is in fact regulated by along-track integration of the WSC (AIWSC). Constrained by atmospheric TC dynamics, the violent winds outside the radius (R-max) of maximum wind of any TC must have nearly zero WSC. Consequently, the AIWSC function can befit as a boxcar function with an extraordinarily large positive value between +/- R-max about the track. Based on this boxcar function, the theoretical estimate of the cross-track length scale of the baroclinic geo-strophic response, L-d + R-max, is presented, where L-d is the first-mode baroclinic Rossby deformation radius. Further, this scale is validated by numerical experiments to well explain the width of the altimetry-observed geostrophic response induced by any TC. Evidently, L-d + R-max is far smaller thanR(17) and thus the baroclinic geostrophic response generally has a limited width. This study implies that, although for a TC the violent winds outside R-max are generally similar to 90% of all winds, in an open ocean these winds may be useless to perturb the ocean interior due to the nearly zero WSC