Simulated and observed updrafts and downdrafts in Hurricane Dennis (2005): Relationship to intensity

This research investigates how distributions of updrafts and downdrafts vary with Dennis's intensity in both a Weather Research and Forecasting (WRF) simulation and in observations from research aircraft and remote sensing instruments during the Tropical Cloud Systems and Processes (TCSP) field campaign. Updraft and downdraft evolution is first examined from a WRF run consisting of a 4-domain nested configuration with 1-km grid spacing on the inner domain and cloud microphysical processes represented using an updated scheme. Means and distributions of simulated vertical velocity, reflectivity, and hydrometeor (e.g., graupel, rain, snow) mixing ratios are computed for specific regions (e.g., eyewall, rainbands, convective, stratiform). Contoured frequency by altitude (CFAD) diagrams illustrate differences in these fields between the incipient and mature stages of the simulated tropical cyclone. Distributions of Doppler velocity and reflectivity derived from the WRF simulation are then compared against observations from the ER-2 Doppler radar (EDOP) and the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). The distribution tails (e.g., 99th percentile), which represent isolated, yet rapid, vertical motions are hypothesized to indicate large impacts on latent heat and intensity. In addition to the vertical distributions apparent from CFADs, azimuthal variations of vertical velocities show key relations among updraft speeds, their proximity to the existing vortex center, and Dennis's intensity.