Effects of vertical wind shear on tropical cyclone precipitation

Abstract

The response of the precipitation field for tropical cyclones in relation to the surrounding environmental vertical wind shear has been investigated using~20 000 snapshots of passive-microwave satellite rain rates. Composites of mean rain rates, 95th percentile rain rates, and rain coverage were constructed to compare how the spatial distribution of the precipitation was organized under varying environmental shear. Results indicated that precipitation is displaced downshear and to the left (right for Southern Hemisphere) of the shear vector. The amplitude of this displacement increases with stronger shear. The majority of the asymmetry found in the mean rain rates is accounted for by the asymmetry in the occurrence of heavy rain. Although rain is common in all quadrants of the sheared tropical cyclones, heavy rain (≥8 mm h-1 at the~25-km scale) is comparatively rare in the upshear-right quadrant. It is shown that the effect that shear has on the rain field is nearly instantaneous. Strong westerly shear formed slightly more asymmetric patterns than strong easterly shear. © 2010 American Meteorological Society.