Statistical Analysis of Convective Updrafts in Tropical Cyclone Rainbands Observed by Airborne Doppler Radar

Ten years of airborne Doppler radar observations are used to study convective updrafts' kinematic and reflectivity structures in tropical cyclone (TC) rainbands. An automated algorithm is developed to identify the strongest rainband updrafts across 12 hurricane-strength TCs. The selected updrafts are then collectively analyzed by their frequency, radius, azimuthal location (relative to the 200–850 hPa environmental wind shear), structural characteristics, and secondary circulation (radial/vertical) flow pattern. Rainband updrafts become deeper and stronger with increasing radius. A wavenumber-1 asymmetry arises, showing that in the downshear (upshear) quadrants of the TC, updrafts are more (less) frequent and deeper (shallower). In the downshear quadrants, updrafts primarily have in-up-out or in-up-in secondary circulation patterns. The in-up-out circulation is the most frequent pattern and has the deepest updraft and reflectivity tower. Upshear, the updrafts generally have out-up-in or in-up-in patterns. The radial flow of the updraft circulations largely follows the vortex-scale radial flow shear-induced asymmetry, being increased low-level inflow (outflow) and midlevel outflow (inflow) in the downshear (upshear) quadrants. It is hypothesized that the convective-scale circulations are significantly influenced by the vortex-scale radial flow at the updraft base and top altitudes. Other processes of the convective life cycle, such as bottom-up decay of aging convective updrafts due to increased low-level downdrafts, can influence the base altitude and, thus, the base radial flow of the updraft circulation. The findings presented in this study support previous literature regarding convective-scale patterns of organized rainband convection in a mature, sheared TC.