Bolt from the blue caught on video

A bolt from the blue [1,2] was observed simultaneously by ground-based video observations, space-based video with the Lightning Imager on the Meteosat Third Generation geostationary satellite (MTG-LI) [3,4], and a low-frequency lightning interferometer during field work at Sutherland, South Africa, January 28th, 2025.The bolt from the blue was initiated by an intra-cloud discharge that connects two charged layers at the edge of a thundercloud. The stepped leader subsequently propagates horizontally away from the cloud. During the development, the lightning leader channel splits into two parts, one which propagates further away horizontally and one which returns towards the cloud but then curves down to Earth where it splits again into two separate strike points on the ground.The ground-based video observations are paralleled by simultaneous space-based video observations with the Lightning Imager on the Meteosat Third Generation geostationary satellite (MTG-LI) with a temporal resolution of 1 ms. The illuminations of individual pixels (events) are summarised into clusters (groups) which measure the spatial extent of the bolt from the blue after correction for the parallax error using cloud top height measurements inferred from the Flexible Combined Imager (FCI) payload on MTG.The electromagnetic emissions of the bolt from the blue are recorded with a low-frequency interferometer on the ground that consists of three radio receivers which are deployed in a triangular array, ~15 km away from the thundercloud. The radio receivers use horizontal electric field sensors (horizontal dipoles) [5] to measure the electromagnetic emissions of the bolt from the blue with 1 us resolution. These waveforms show a sequence of pulses with different shapes which indicate the occurrence of various physical processes during the development of the bolt of the blue.The video observations from the ground and from space are compared to the recordings with the lightning interferometer and the benefits arising from these joint analyses are discussed in detail. References:[1] Krehbiel, P., Riousset, J., Pasko, V. et al. Upward electrical discharges from thunderstorms. Nature Geoscience 1, doi:10.1038/ngeo162, 233–237, 2008.[2] J. Harley, L. Zimmerman, H. Edens, H. Stenbaek-Nielsen, R. Haaland, R. Sonnenfeld, and M. McHarg. High-speed spectra of a bolt from the blue lightning stepped leader. Journal of Geophysical Research, 26(3), doi:10.1029/2020JD033884, 1-10, 2021.[3] A.M. Holzer, et al.: EUMETSAT-ESSL Application Guide on the Use of MTG LI in Severe Convective Storms Nowcasting, ESSL Report 2025-01, https://www.essl.org/cms/essl-testbed, 2025.[4] M. Füllekrug, E. Williams, C. Price, S. Goodman, R. Holzworth, S.-E. Enno, and B. Viticchie, Novel lightning flash densities from space [in “State of the Climate in 2024”, Bulletin of the American Meteorological Society, 106 (8), doi:10.1175/2025BAMSStateoftheClimate.1, S85–S86, 2025.[5] M. Füllekrug, M. Kosch, G. Dingley, X. Bai, and L. Macotela. Six-component electromagnetic wave measurements of sprite-associated lightning. ESS Open Archive, doi:10.22541/essoar.176296584.41929367/v1, 2025. Acknowledgments: The authors wish to thank Sven-Erik Enno from EUMETSAT for assistance with the MTG-LI data retrieval. The MTG-LI data used for this study were kindly provided by EUMETSAT from https://user.eumetsat.int/resources/user-guides/mtg-data-access-guide