Validation and Sensitivity Testing of a Lightning Grouping Algorithm on Thunderstorm Climatologies

Thunderstorms and lightning are well-known hazards to life and property, especially in vulnerable urban areas. Automated, ground-based lightning observational networks have high detection efficiencies, and lightning's genesis is exclusively associated with cumulonimbus development.

The presented ongoing research builds on the development of a lightning grouping algorithm used to identify thunderstorm events in the Washington D.C. region from 12 years of National Lightning Detection Network (NLDN) data. More than 7 million flashes were used in a cell search algorithm to assign thunderstorm events based on spatiotemporal proximity of flashes and to assemble thunderstorm climatologies.

While the overall project is aimed at analyzing relationships between aerosols and urban thunderstorm electrification, here we focus on testing the algorithm and validating its method of grouping flashes into events. To do this, the threshold for space and time that separates events was modified to determine the sensitivity of detected event number and size to parameter choice. Additionally, specific events are selected as case studies and compared to meteorological data including the National Weather Service NEXRAD to validate the algorithm.

Preliminary results show the algorithm to be particularly sensitive to spatial threshold changes, whereas changes in the spatio-temporal tradeoff parameter (i.e. requiring spatially more distant flashes to be close in time and vice-versa) appears to only have limited importance on thunderstorm event counts and thus observed thunderstorm climatologies.