Lightning Density and Its Coupled Covariates Within the Continental United States

Abstract

Lightning is a critical climate variable, due to both its significance as a metric of atmospheric thresholding and its significance as a natural hazard. While lightning density is often studied as a marker of local convective dynamics, it is also a player in the larger coupled systems linking the local atmospheric column, the land surface, and dynamic moisture advection. Aiming to bridge the land-atmosphere gap in lightning studies, the research investigates the interplay between soil moisture (SM), convective available potential energy (CAPE), precipitation, wind shear, atmospheric moisture, and lighting density. Employing spatial correlations (r) and year-over-year change analyses, satellite (SMAP) and reanalysis (ERA5 and NARR) data from 2016 to 2021 show the seasonal and interannual co-evolution of lightning and its land-atmosphere covariates. Across the continental United States (CONUS), CAPE was identified as the most effective proxy for lightning density, particularly in summer (r = 0.80). Notably, the southeastern U.S. displayed a significant connection between SM and lightning (r = 0.60), representing the role of thunderstorms in seasonal land surface moisture as well as feedbacks from the land surface to convective processes upstream of lightning. In contrast, the arid southwestern U.S., another region of high thunderstorm occurrence, exhibited reduced correlations with SM (r = 0.12), likely due to both the reduced persistence of moisture anomalies in arid regions and the relatively weaker land surface feedbacks compared to the influence of advection by the North American monsoon. The coupling of SM was most pronounced in the southeastern U.S. during the summer months (JJA), while no clear pattern was identifiable elsewhere within CONUS. Wavelet analyses suggest seasonal changes in the lead-lag behavior of SM and lightning density, with SM commonly leading in the Southeast in JJA. Year-to-year change analysis during JJA revealed aligning trends, reinforcing the relationship between summertime SM and lightning. This study provides a baseline reference for coupled land and atmosphere feedbacks between terrestrial lightning, its precursors, and its effects.