Tornado Damage Estimation Using Polarimetric Radar

Abstract

This study investigates the use of tornadic debris signature (TDS) parameters to estimate tornado damage severity using Norman, Oklahoma (KOUN), polarimetric radar data (polarimetric version of the Weather Surveillance Radar-1988 Doppler radar). Several TDS parameters are examined, including parameters based on the 10th or 90th percentiles of polarimetric variables (lowest tilt TDS parameters) and TDS parameters based on the TDS volumetric coverage (spatial TDS parameters). Two highly detailed National Weather Service (NWS) damage surveys are compared to TDS parameters. The TDS parameters tend to be correlated with the enhanced Fujita scale (EF) rating. The 90th percentile reflectivity, TDS height, and TDS volume increase during tornado intensification and decrease during tornado dissipation. For 14 tornado cases, the maximum or minimum TDS parameter values are compared to the tornado's EF rating. For tornadoes with a higher EF rating, higher maximum values of the 90th percentile Z HH , TDS height, and volume, as well as lower minimum values of 10th percentile r HV and Z DR , are observed. Maxima in spatial TDS parameters are observed after periods of severe, widespread tornado damage for violent tornadoes. This paper discusses how forecasters could use TDS parameters to obtain near-real-time information about tornado damage severity and spatial extent.

Some Considerations for the Use of High-Resolution Mobile Radar Data in Tornado Intensity Determination

“…In the tornadic debris field, r hv is markedly reduced (e.g., Ryzhkov et al 2005;Kumjian and Ryzhkov 2008;Bluestein et al 2007a;Snyder et al 2010;Bodine et al 2013). The signals from the H and V channels are therefore less correlated than in areas composed of purely meteorological scatterers.…”

“…In rain, r hv $ 0.98 at common radar frequencies, and it generally decreases in areas of mixed-phased precipitation or hail (e.g., Balakrishnan and Zrni c 1990;Straka et al 2000). In general, nonmeteorological scatterers such as biological scatterers (e.g., Zrni c and Ryzhkov 1999) and tornado debris (e.g., Ryzhkov et al 2005;Bodine et al 2013) are associated with r hv , 0.7. The specific propagation differential phase can be calculated from scattering amplitudes as…”

Bootstrap Dual-Polarimetric Spectral Density Estimator

“…To effectively assess the potential damage , it is important to have accurate measurements to estimate the intensity of the tornado. Ryzhkov et al (2005) catalogued typical values of the polarimetric radar variables associated to the TDS as Z > 45 dBZ, Z DR < 0.5 dB, and ρ HV < 0.8, while Bodine et al (2013) use more stringent sets of values for Z and ρ HV : either Z < 43 dBZ and ρ HV < 0.82, or Z < 51 dBZ and ρ HV < 0.72. With these criteria, it can be inferred that TDS are more likely to be seen in observations due to the debris signal dominating in a particular radar resolution volume (Ryzhkov et al 2005), thus the mean radial velocities in volumes with TDS are more prone to centrifuging biases.…”

“…Additionally, they are clear indicators of tornadoes when ground observation is limited or impossible (e.g., at night or during heavy rainfall) (Kumjian and Ryzhkov 2008). A set of values typically found to be associated with TDS is suggested in Ryzhkov et al (2005) and Bodine et al (2013), though it is still unknown exactly how the characteristics of different debris types affect different polarimetric radar measurements.…”

Potential Tornado Warning Improvement Resulting from Utilization of the TDS in the Warning Decision Process

“…Tornadic debris signatures (TDSs) are well-known features that may be present when a strong wind field lofts debris to the altitude of the radar beam (e.g., Ryzhkov et al 2005;Schultz et al 2012a;Bodine et al 2013;Saari et al 2014;Van Den Broeke and Jauernic 2014;Van Den Broeke 2015). They are most repeatably characterized by a radial velocity couplet, and by enhanced reflectivity factor at horizontal polarization (Z HH ) collocated with depressed co-polar cross-correlation coefficient (ρ hv ).…”