1,1,2,3,1,1,5,- 1Netherlands Institute for Radio Astronomy (ASTRON), Dwingeloo, The Netherlands
- 2University Groningen, Kapteyn Astronomical Institute, Landleven 12, 9747 AD Groningen, The Netherlands
- 3Interuniversity Institute for High-Energy, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- 4State Key Laboratory of Severe Weather Meteorological Science and Technology, CMA Key Laboratory of Lightning, Chinese Academy of Meteorological Sciences, Beijing, China
- 5University of New Hampshire, Department of Physics and Astronomy, Rochester, United States of America
- 6Department of Electrical and Computer Engineering, Duke University, Durham, NC, USA
We present observations of small-scale discharges, or sparks, within thunderstorms before the initiation of a lightning leader. Using LOFAR A-TRID, which provides exceptional precision and accuracy through near-field beamforming with hundreds of antennas [1], we detected multiple spark-like discharges with varying characteristics. Some show a collective propagation direction, with some speeds as low as 1 x 106 m/s (similar to ultra-slow propagation), and some as fast as 1 x 107 m/s [2, 3]. As these sparks occur in a kilometer sized region adjacent to the initiation region, they could be used to map the extent of high-field regions within thunderstorms. These results suggest that failed initiation events may be infrequent and difficult to detect as they occur in sparse clusters on short spatiotemporal scales. This work will provide an overview of the physical properties of the spark discharges and implications for lightning initiation.
1: Olaf Scholten, Steven A. Cummer, Joseph R Dwyer, et al. A Comprehensive analysis of High Resolution VHF Observations with LOFAR of the Positive Initiating Event for Several Lightning Flashes. ESS Open Archive . December 12, 2025.
2: Sterpka, C., Dwyer, J., Liu, N., Demers, N., Hare, B. M., Scholten, O., & ter Veen, S. (2022). Ultra-slow discharges that precede lightning initiation. Geophysical Research Letters, 49, e2022GL101597. https://doi.org/10.1029/2022GL101597
3: terpka, C., Dwyer, J., Liu, N., Hare, B. M., Scholten, O., Buitink, S., et al. (2021). The spontaneous nature of lightning initiation revealed. Geophysical Research Letters, 48, e2021GL095511. https://doi.org/10.1029/2021GL095511
How to cite: Sterpka, C., Hare, B., Scholten, O., Turekova, P., Lourens, M., Wu, B., Dwyer, J., Liu, N., and Cummer, S.: Small-Scale Discharges in the Thunderstorm Prior to Lightning Initiation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13571, https://doi.org/10.5194/egusphere-egu26-13571, 2026.
