Are you comfortable with looking at RadarScope data and finding hook echoes and areas of rotation? If so, the next step is to learn how to use dual-polarization products to look for debris being lofted by a tornado. Let’s take a look at how to pick out a Tornado Debris Signature (TDS).
CONFIRMED Tornado in heart of Pennsylvania created a TDS on radar!
This Tuesday, an EF-1 #Tornado lofted debris high enough to create a “Tornado Debris Signature”. Here’s the FULL event seen on Radarscope through the State College radar site!#pawx #thinkweather #damage #wx pic.twitter.com/1rlyJPmhgm
— Nash from Nashville (@NashWX) August 22, 2018
As a tornado lofts debris above the ground, it can create a signature in differential reflectivity and correlation coefficient data. First, take a look at reflectivity and Storm Relative Velocity data of a supercell that produced a tornado in Marshalltown, Iowa. It’s relatively easy to see the hook here and the associated rotation couplet.
Marshalltown, Iowa Supercell Reflectivity and Storm Relative Velocity
A debris signature must be located near the hook echo of the supercell. These signatures generally have low differential reflectivity values. The low values (circled in green) are due to the random orientation of objects being lofted.
Marshalltown, Iowa Supercell Differential Reflectivity
Correlation coefficient values in or near the hook echo associated with debris signatures are also low (less than 0.8). These values confirm that the echoes being observed are non-meteorological. In the image below, the area of low correlation coefficient values is circled in green.
Marshalltown, Iowa Supercell Correlation Coefficient
Comparing the correlation coefficient to the reflectivity and differential reflectivity images above, it is likely that the radar is observing debris being lofted by a tornado.
Photos of the tornado damage in Marshalltown, Iowa. Photos captured from the Iowa Storm Chasing Network via live stream. #iawx #iowa #tornados #marshalltown pic.twitter.com/EIIhPyrJES
— Thomas Stuckey-Mounter (@tsmounter) July 19, 2018
A TDS can provide an indication that a storm is causing damage, but there are some important limitations to keep in mind. For instance, a tornado could be occurring without lofting debris. In addition, it is possible that a tornado is occurring, but the debris is not being lofted high enough to be detected by radar.
Radar observations can provide insight into the processes occurring in a storm. Tornado Debris Signatures can serve as an indication of how a storm is affecting the area it is impacting.