Satellite-derived rain rates in vertically sheared tropical cyclones

[1] When tropical cyclones interact with environmental vertical wind shear, they often take on an asymmetric structure. Prior observational and modeling studies have identified a preference for rainfall enhancement in the directions that are down shear and also to the left of the shear vector (in the Northern Hemisphere). This study composites hundreds of snapshots of the rain fields for Atlantic tropical cyclones between 1988-2004, taken from satellite-borne passive microwave radiometer estimates. Quadrant mean rain rates are fairly symmetrical in weakly sheared hurricanes. For cases with shear greater than 10 m s(-1), the favored downshear and left-of-shear quadrants have a factor of two greater rain rates in the inner core than the non-favored quadrants. Beyond 100 km from the center, this asymmetry increases to a factor of four or more. The magnitude of the asymmetry is greater for tropical storms, although the mean rain rates are less.