Morgan Schneider - February 4

Convective Meteorology (Mesoscale Dynamics)

A Novel Technique to Correct Debris-Related Bias in Velocity Measurements from Tornadoes

Morgan Schneider

Friday, February 4

3:30 PM

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https://meet.google.com/iru-ggiv-afj

Debris centrifuging in tornadoes is known to cause bias in radar measurements of tornadic wind speeds.  Debris presence in a radar volume is associated with anomalous radial divergence, underestimation of azimuthal wind speeds, and negative bias in vertical velocity from single- and dual-Doppler retrievals, resulting in potentially erroneous interpretations of tornado intensity and structure from Doppler velocity observations.  To mitigate this bias, a simulation-based framework is used to develop a spectral technique for Doppler velocity correction.  This novel method utilizes dual-polarization spectral density estimation, fuzzy logic classification, and spectral filtering in order to reduce debris-related bias in radar observations.  Spectral polarimetric characteristics of a signal are analyzed, and velocity components in the spectrum are classified as either rain or debris motion using fuzzy logic.  The Doppler spectrum is then filtered to suppress debris-dominated motion and obtain a new, corrected velocity estimate.

Results from this method show promising potential for the mitigation of debris-induced velocity bias in tornadoes.  Velocity correction algorithms are applied to simulated PPI sector scans generated from SimRadar, a realistic polarimetric radar time-series simulator, and their performance is evaluated by comparing the pre-correction and post-correction velocity bias.  Overall, the correction algorithms consistently reduce velocity bias to near 0 m/s across most of the simulated sector domain, with the exception of the region at the center of the vortex, where debris concentrations tend to be highest.  These algorithms have also been applied to an observational data set from KOUN from the Moore, Oklahoma tornado on 20 May 2013.  The corrected Doppler velocities are consistently larger in magnitude compared to the original measured velocities near and within the central tornadic circulation.  Given that debris is typically associated with underestimation of azimuthal wind speeds, these results suggest that the velocity correction algorithms can successfully reduce debris-related bias in observed Doppler velocities from tornadoes.