Eisenacher et al. (2025) Lightning Density and Its Coupled Covariates Within the Continental United States

Identification

• Journal: Earth and Space Science
• Year: 2025
• Date: 2025-09-01
• Authors: Steffen Eisenacher, Anke Fluhrer, Jan Bliefernicht, Daniel J. Short Gianotti, Harald Kunstmann, Thomas Jagdhuber
• DOI: 10.1029/2025ea004207

Research Groups

• Institute of Geography, University of Augsburg, Augsburg, Germany
• German Aerospace Center (DLR), Microwaves and Radar Institute, Weßling, Germany
• Department of Civil and Environmental Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
• Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Garmisch‐Partenkirchen, Germany

Short Summary

This study investigates the coupled land-atmosphere interactions influencing lightning density across the Continental United States (CONUS), finding that Convective Available Potential Energy (CAPE) is the most effective proxy for lightning, while soil moisture (SM) shows a significant, seasonally-dependent coupling with lightning, particularly in the southeastern U.S.

Objective

• To investigate the interplay between soil moisture (SM), convective available potential energy (CAPE), precipitation, wind shear, atmospheric moisture, and lightning density across the Continental United States (CONUS) to bridge the land-atmosphere gap in lightning studies.

Study Configuration

• Spatial Scale: Continental United States (CONUS), analyzed at 0.5° spatial resolution, with specific focus on nine climate regions and two high-thunderday pixel clusters.
• Temporal Scale: Monthly and seasonal (MAM, JJA, SON, DJF) resolutions from 2016 to 2021, with wavelet coherence analysis performed on daily data for lead-lag relationships.

Methodology and Data

• Models used: Integrated Forecast System (IFS) numerical model (within ERA5), NCEP Eta Model (within NARR).
• Data sources:
  • Lightning Density (LD): World Wide Lightning Location Network (WWLLN) / WWLLN Global Lightning Climatology (WGLC) (ground-based, 0.5° spatial resolution, daily).
  • Soil Moisture (SM): Soil Moisture Active Passive (SMAP) Level 3 Radiometer Soil Moisture Version 8 (SPL3SMP) (satellite, 36 km spatial resolution, daily).
  • Convective Available Potential Energy (CAPE), Total Column Water Vapor (TWV), Precipitation (P): ERA5 reanalysis (0.25° spatial resolution, 6-hourly).
  • Vertical Wind Shear (VWS): North American Regional Reanalysis (NARR) (0.25° spatial resolution, 6-hourly).
  • Standardized Precipitation-Evapotranspiration Index (SPEI): Global SPEI Database (model, 0.5° spatial resolution, 1-month).
  • Land Cover: National Land Cover Database (NLCD) (satellite, 30 m spatial resolution, 3-year intervals).
• Statistical Methods: Spatial Pearson correlation coefficients (r), year-over-year change analysis (Δx), masked correlations (e.g., for upper decile of thunderdays), time series and scatterplots, Wilcoxon rank-sum tests, and Wavelet Coherence Analysis (WCA).

Main Results

• CAPE is consistently the most effective proxy for lightning density across CONUS, especially in summer (average r = 0.80 across high-thunderday pixels in the Southeast, reaching r ≈ 0.9 in the Southeast during summer).
• Soil moisture (SM) shows a strong positive coupling with lightning density in the southeastern U.S. (average r = 0.60 in summer for high-thunderday pixels), where SM often leads lightning by a fraction of a day in summer and fall.
• In contrast, the arid southwestern U.S. (another region of high thunderstorm occurrence) exhibits a much weaker correlation between SM and lightning density (average r = 0.12), likely due to stronger monsoonal advection and orographic lifting.
• Vertical wind shear (VWS) shows modest to weak correlations with lightning density, with a slight negative correlation in the Southeast (r = -0.16 seasonally for high-thunderday pixels), consistent with air-mass thunderstorms in low-shear environments.
• Year-over-year changes in SM are significantly associated with lightning density changes in 2 out of 5 years, while CAPE changes are significant in 4 out of 5 years, indicating CAPE's stronger influence on interannual lightning variability.
• Lightning density (LD, total strokes) correlates more strongly with SM and CAPE than weighted lightning density (LDw, intensity per storm), suggesting SM is more tied to the frequency of thunderstorm occurrences than the intensity of individual storms.

Contributions

• Provides a baseline reference for coupled land and atmosphere feedbacks between terrestrial lightning, its precursors, and its effects across CONUS.
• Bridges the land-atmosphere gap in lightning studies by systematically investigating the role of soil moisture alongside atmospheric covariates.
• Highlights significant regional differences in land-atmosphere coupling for lightning, particularly contrasting the humid Southeast with the arid Southwest.
• Demonstrates seasonal lead-lag relationships between soil moisture and lightning, suggesting soil moisture anomalies can precede lightning anomalies.
• Emphasizes the distinction between total lightning occurrence and lightning intensity in their relationships with land-atmosphere variables.

Funding

• The authors gratefully acknowledge the use of multiple open-access data sets that enabled this research, specifically mentioning Kaplan and Lau for providing the global gridded lightning climatology data set.
• Open Access funding enabled and organized by Projekt DEAL.

Citation

@article{Eisenacher2025Lightning,
  author = {Eisenacher, Steffen and Fluhrer, Anke and Bliefernicht, Jan and Gianotti, Daniel J. Short and Kunstmann, Harald and Jagdhuber, Thomas},
  title = {Lightning Density and Its Coupled Covariates Within the Continental United States},
  journal = {Earth and Space Science},
  year = {2025},
  doi = {10.1029/2025ea004207},
  url = {https://doi.org/10.1029/2025ea004207}
}