Quadrant distribution of tropical cyclone inner-core kinematics in relation to environmental shear

Abstract

Airborne Doppler radar data collected in tropical cyclones by National Oceanic and Atmospheric Administration WP-3D aircraft over an eight-year period (2003-2010) is used to statistically analyze the vertical structure of tropical cyclone eyewalls with reference to the deep layer shear. Convective evolution within the inner core conforms to patterns shown by previous studies: convection initiates downshear-right, intensifies downshear-left and weakens upshear. Analysis of the vertical distribution of radar reflectivity and vertical air motion indicates the development of upper-level downdrafts in conjunction with strong convection downshear-left and a maximum in frequency upshear-left. Intense updrafts and downdrafts both conform to the shear asymmetry pattern. While strong updrafts occur within the eyewall, intense downdrafts show far more radial variability, particularly in the upshear-left quadrant, though they concentrate along the eyewall edges. Strong updrafts are collocated with low-level inflow and upper-level outflow superimposed on the background flow. In contrast, strong downdrafts occur in association with low-level outflow and upper-level inflow.