Lightning Evolution in Hailstorms From the Geostationary Lightning Mapper Over the Contiguous United States

As two metrics that depict convection features, lightning and hail are generated through different physical mechanisms but are related. The Geostationary Lightning Mapper (GLM) provides a unique approach to monitoring and studying the continual evolution of lightning in hailstorms. In this study, 3 years of GLM observations were used to analyze the lightning evolution in hailstorms over the contiguous United States. The lightning rate had two peaks at -2 min (t1) (relative to the hail occurrence time) and 59 min (t3), with a valley at 23 min (t2). The lightning rates of large hail were lower at t1 and higher at t2 than those of small hail. The maximum lightning rate grid generally moved from northwest to southeast but suddenly moved westward around 23 min. Observations of WWLLN confirmed these results but also highlighted differences, such as the high ratio between the WWLLN and GLM lightning rates around t1 and t3. The events per flash and flash duration/area/energy showed opposite variations with lightning rate, and their low values were accompanied by high lightning rate and low detection efficiency of GLM relative to WWLLN. However, the event energy continued to decrease with two local maxima at approximately t1 and t3. Furthermore, if the regional event rate was used in the lightning jump (LJ) algorithm, LJs preceded 71% of the hail reports, and the mean lead time reached 29 min. These results provide new insights into lightning features in hailstorms and verify the performance of the GLM in studying and monitoring hailstorms. Plain Language Summary Hail and lightning are two kinds of common phenomena that occur in convection cells and are both used as metrics to measure convection intensity. However, they are generated via different microphysical processes and the literature has shown their different spatial distribution patterns in many regimes, including the CONUS. Here, we used the observations from the Geostationary Lightning Mapper (GLM) to investigate how lightning evolves during hailstorms. The temporal evolution of lightning rate shows a two-peak and one-valley feature. Lightning rate began to drop 2 min before hail occurrence time and reached a local minimum of around 23 min. Spatially, the location with the highest lightning rate moved from northwest to southeast, but suddenly moved 0.2 degrees to west around 23 min. Moreover, the lightning rates of large hail were lower at the first peak and higher at the second peak than those of small hail. Other lightning features, such as flash energy, flash area, and flash duration, were highly related to event counts per flash and showed opposite variations with the lightning rate, resulting in two-valley and one-peak features over time. These results would promote our understanding in lightning and hail processes and aid in monitoring severe convection with the GLM.