Investigating the Characteristics and Dynamics of Convective Updrafts in Observed and Simulated Tropical Cyclone Rainbands

This study uses the airborne Doppler radar data set, TC-RADAR, and model simulations from the Penn State Ensemble Kalman Filter data assimilation system to examine the dynamics and evolution of tropical cyclone (TC) rainband convective updrafts. This examination utilizes an updraft selection algorithm and statistical analysis of convective updraft characteristics previously developed based on observations of TC rainband convective updrafts. The selected updrafts are collectively analyzed by their spatial frequency, radius, azimuthal location (relative to the environmental 200–850 hPa wind shear and environmental 850 hPa mean flow), structural characteristics, and secondary circulation (radial/vertical) flow pattern. The observed updrafts compare favorably with the simulated updrafts. A wavenumber-1 asymmetry is found, showing that convective updrafts in the downshear quadrants of the TC are more frequent. The radial flow of updraft circulations aligns with the prevailing vortex-scale radial flow, which is governed by the environmental shear or low-level mean flow-induced asymmetry. Convective-scale circulations are hypothesized to be significantly influenced by vortex-scale radial flow at the updraft base and top altitudes. The bottom-up decay of aging convective updrafts, caused by increased low-level downdrafts, affects the base altitude and the subsequent radial flow of the updraft circulation. The findings presented in this study support previous literature regarding observed convective-scale patterns of organized rainband convection in a mature TC.