Radar applications for nowcasting lightning cessation

Determining the duration of threat posed by lightning is a high priority for all outdoor activities and especially a leading concern of day-to-day operations for the 45th Weather Squadron (45WS) for Kennedy Space Center (KSC) and the Cape Canaveral Air Force Station (CCAFS). The University of Alabama in Huntsville (UAHuntsville) and NASA's Marshall Space Flight Center (MSFC) are collaborating with the 45WS to enable improved nowcasting of lightning cessation through radar applications. This project centers on use of dual-polarimetric radar capabilities and places special emphasis on the development of a physically based operational algorithm to predict lightning cessation. Data from the UAHuntsville Advanced Radar for Meteorological and Operational Research (ARMOR) along with the NASA-MSFC North Alabama Lightning Mapping Array are used in this study to investigate the radar signatures present before and after lightning cessation.

Polarimetric radar variables offer the possibility to improve upon existing statistically based cessation algorithms through the inclusion of physically meaningful trends reflecting interactions between in-cloud electric fields and microphysics. While previous studies have investigated the pairing of temperature/height and reflectivity thresholds, this study is based on decades of polarimetric radar research which has shown that propagation differential phase can be used to determine the presence of distinct phase and ice crystal alignment signatures in the presence of strong electric fields associated with lightning. This study determines the extent these ice-crystal alignment signatures (determined from polarimetric data) can be used to nowcast the cessation of lightning activity within a given thunderstorm. These results are compared to the Volume Averaged height Integrated Radar Reflectivity (VAHIRR) algorithm which was originally developed during the Airborne Field Mill II research project and utilizes horizontal reflectivity as a baseline to determine if the addition of polarimetric radar data shows improvement to the prediction of lightning cessation. A summary of results and a discussion of the feasibility of an operational algorithm will be presented.