On Issues Related to the Manual Identification of ZDR Arcs in Simulated Supercell Thunderstorms

ON ISSUES RELATED TO THE MANUAL IDENTIFICATION OF ZDR ARCS IN SIMULATED SUPERCELL THUNDERSTORMS

Raychel Nelson*¹, Allison LaFleur¹, and Robin Tanamachi¹

Purdue University, West Lafayette, IN 47907

*kelle192@purdue.edu

We report progress on a project to manually identify simulated ZDR arcs for comparison to those produced by automated identification. It has been hypothesized that areal extent and intensity of differential reflectivity (ZDR) arcs change before tornadogenesis, potentially providing forecasters with insight into the likelihood of a tornado. In this experiment, nine simulated tornadic and nine simulated non-tornadic storms were analyzed. The ZDR field was visualized at a height of 500 m AGL, and the perimeter of the ZDR arc was manually enclosed with line segments. We identified ZDR arcs in each simulation at 1-min intervals for a period of 15 min prior to the time of tornadogenesis (failure). We will show examples of identified ZDR arcs, as well as their development throughout the life of the storm.

Manual identification of ZDR arcs by a trained researcher is required in order to validate the automated methods of identifying these arcs. However, manual identification posed some challenges. In instances of hail fallout or mesocyclone cycling, ZDR arcs can become bisected, and the program used can currently only trace one arc each time it is run. Another source of ambiguity is multiple areas of high ZDR within one storm. We will show examples of these types of complex ZDR arcs, as well as outlining our plans to compare them to two automated methods of ZDR arc identification. It is our hope that this work will illuminate issues pertinent to the early identification of pretornadic ZDR arcs in supercells.