Automated Identification of Storm Electrification Signatures Using Polarimetric Radar Observations

Severe weather events often produce significant lightning discharges that can result in harmful impacts to society. Several research efforts have investigated polarimetric radar signatures in thunderstorms to advance the understanding of storm electrification. However, given the short life span of lightning (i.e., 50 - 200 ms), conventional weather radars fail to capture detailed, volumetric, polarimetric signatures of storm electrification. Rapid-scanning radars can provide more information about electrified storm regions, their evolution, and could potentially help locate lightning strikes in the absence of other data.

The Horus radar system is an S-band, fully digital, polarimetric phased array radar capable of implementing rapid-scanning modes, unique for lightning observations. These rapid updates allow high-temporal resolution observations closer to the timescales of lightning discharges. Two polarimetric signatures associated with lightning have been documented: one caused by plasma reflection from the lightning discharge itself, the other caused by ice alignment above the melting layer in regions with large, vertical electric fields. The former one is nearly instantaneous, occurring only during a lightning discharge, and produces distinctive radially oriented polarimetric signatures in reflectivity (Z_h) and correlation coefficient (ρ_HV). The latter one is present for a longer period, and results in large regions of negative specific differential phase (K_DP) and differential reflectivity (Z_DR) above the melting layer.

In this research, we investigate the occurrence of both lightning signatures on polarimetric data from the Horus radar, and develop an algorithm to detect them. Different criteria are used for each type of signature. For the plasma signature, we consider the scan-to-scan change in Z_h and ρ_hv. In contrast, for the ice-alignment signature, we evaluate the change in negative K_DP volumes, which can rapidly become positive after a discharge. This presentation will include preliminary results on what percentage of flashes are captured by these techniques.