The use of dual polarimetric tornadic debris signatures in an operational setting
Schultz, Christopher J; Schultz, Elise V; Darden, Christopher B; Carcione, Brian C; Crowe, Christina C

Additional Authors:
David J. Nadler, NWS Huntsville, Huntsville, AL
Lawrence D. Carey, Earth System Science Center, UAHuntsville, Huntsville, AL
Walter A. Petersen, NASA Marshall Space Flight Center, Huntsville, AL
Patrick N. Gatlin, Earth System Science Center, UAHuntsville, Huntsville, AL
Kevin R. Knupp, Department of Atmospheric Science, UAHuntsville, Huntsville, AL

As dual polarimetric observations become more abundant on the national scale, it will be important for operational forecasters to utilize the bevy of new information to enhance hazardous weather warnings. One such use will be detection of tornadoes as they are happening. While dual polarimetric tornadic debris signatures (DPTDS) cannot provide any lead time on a tornado event, it can be used to confirm that a tornado is occurring; thus allowing an operational forecaster to strengthen the wording within a warning, and the local media to communicate the immediate threat to the public. Previous research on DPTDSs have focused on the use of a combination of horizontal reflectivity (ZH), radial velocity (Vr), differential reflectivity (ZDR) and cross correlation coefficient (ρhv) to detect tornadoes; but this presentation intends to fill a hole in previous work by demonstrating through the use of observed events of how the DPTDS can be used in real-time.

A unique collaboration exists between the National Weather Service (NWS) in Huntsville and the University of Alabama-Huntsville (UAHuntsville), where the NWS office receives real-time dual polarimetric radar data from UAHuntsville s Advanced Radar for Meteorological and Operational Research (ARMOR) C-band dual polarimetric radar. Since February of 2008, nearly a dozen tornadic debris signatures have been observed by the ARMOR radar, with several of these disseminated in real-time to the NWS Huntsville and local media. This dissemination has led increased confidence in the warning decision making process through confirmation of the tornado, leading to stronger worded warnings, and provided the media valuable site specific information that they could use to highlight the population which was in the most danger. These signatures have also been used in post event storm surveys to discover additional areas to examine for damage, where the local emergency manager may not have received any reports. This signature would also aid the immediate response to the disaster by directing resources to areas where the DPTDS was observed.

Herein, we present multiple examples of the DPTDS from a variety of thunderstorm types (e.g., classic supercell, high precipitation supercell, quasi linear convective systems, and broken convective lines), over a range of tornado strengths (EF-1 to EF-5), and at various distances from the radar. Ranges of rhohv values within the observed DPTDS will be compared to the type of damage observed at the ground (vegetation vs structural). Finally, several caveats will be presented to ensure that data with known biases/issues (non-uniform beam filling, gradients in φDP, attenuation, beam blockages) are not mistaken for DPTDSs.