Improving Vertical Velocity Retrievals from Doppler Radar Observations of Convection

 

Authors

Nathan Dahl — University of Oklahoma
Alan Shapiro — University of Oklahoma
Corey Potvin — NOAA - National Severe Storms Laboratory
Joshua Gebauer — Cooperative Institute for Mesoscale Meteorological Studies
Adam Theisen — Argonne National Laboratory

Category

Convective clouds, including aerosol interactions

Description

For many investigations, the vertical velocity (w) field is of prime meteorological importance. However, the vertical velocity component is the most difficult to accurately synthesize from Doppler wind observations, particularly when data are unavailable at low levels. Improvement may be obtained by including a vertical vorticity constraint in the dual-Doppler analysis (Shapiro et al., JTECH, 2009). To apply this constraint, we estimate the local vertical vorticity tendency by obtaining provisional retrievals of the horizontal wind field (and hence the vertical vorticity field) at multiple sample times near the analysis time and then applying either simple local time discretization (the “brute force” method) or spatially-variable advection correction (Shapiro et al., J. Atmos. Sci., 2010). To validate the procedure, we perform dual-Doppler analyses (with and without lower-level data denial) on synthetic ARM radar observations of a simulated supercell. With data denial, the accuracy of the dual-Doppler analysis deteriorates in terms of both the updraft strength and the w RMS error. Improvement from the vorticity constraint depends on the radar scan rate, although the results using spatially-variable advection correction for the local vorticity tendency are noticeably more robust to increased scan time than the results relying on the “brute force” method. Results such as these may provide vital information for planning scanning strategies for field projects such as the Short Convective Campaign.