Report from the ISSI Team #477 “Radiation Belt Physics From Top To Bottom: Combining Multipoint Satellite Observations And Data Assimilative Models To Determine The Interplay Between Sources And Losses” led by led by J.-F. Ripoll (CEA, France), G. D. Reeves (Los Alamos National Laboratory, USA) & D. L. Turner (Applied Physics Laboratory, USA)
Lightning superbolts are the most powerful and rare lightning events with intense optical emission, first identified from space by the Vela satellites at the end of the 70s. Recently, radio frequency superbolts were geographically localized by the very low frequency (VLF) ground stations of the World-Wide Lightning Location Network (WWLLN). Interestingly, the distribution of superbolt locations and occurrence times was not equivalent to that of ordinary lightning: instead, superbolts were found to occur over oceans and seas at a much higher rate, and more often in winter [Holzworth et al., 2019].
In our new study just published in Nature Communications (Ripoll et al. 2021), we show for the first time superbolt very low frequency (VLF) electromagnetic (EM) power density in space from the measurements of the NASA Van Allen Probes mission. We combine space and ground-based measurements of superbolt from CEA, WWLLN, and Météorage ground-based stations in a unique manner to follow electromagnetic superbolt signals from Earth to space over thousands of kilometers. We succeed to widely characterize their VLF electric and magnetic wave power density in space and on Earth, to compute ground-space transmitted power ratio, and to extract various statistical electromagnetic properties of lightning superbolts never before reported.
We find superbolts transmit 10-1000 times more powerful very low frequency waves into space than typical strokes, revealing their extreme nature in space. We conclude that superbolts exhibit several properties that differ from ordinary lightning (Ripoll et al., 2020), other than their geographic and seasonal distribution, deepening the mystery associated with these extreme events. They have, for instance, a more symmetric first ground-wave peak due to a longer rise time, larger peak current, weaker decay of electromagnetic power density in space with distance, and a power mostly confined in the very low frequency range. Reasons are not yet established. Our study should guide modelling and understanding of lightning electrodynamics, atmospheric discharges, and wave transmission from Earth to space, with applications in remote sensing, and wave modeling in space for radiation belt physics. Simultaneous optical and electromagnetic observations should be critical to help reveal more mysteries of superbolts.
Image showing wave power in space: electromagnetic (EM) signature of a 1.2 MJ superbolt measured from the Van Allen Probes. (a) burst mode electric field power spectral density (PSD in V2/m2/Hz) versus time, (b) the evolution of the measured electric field power and estimated wave power of WWLLN-detected lightning strokes in the time window (green circles #2-#10 and superbolt with red contour).
The studies on lightning (Ripoll et al., 2020) and on superbolts (Ripoll et al., 2021) electromagnetic power have been conducted by scientists from CEA in France, the University of Colorado, the Los Alamos National Laboratory, the university of Iowa, the University of Minnesota, and the Météorage Company.
References
Ripoll, J.‐F., Farges, T., Malaspina, D. M., Lay, E. H., Cunningham, G. S., Hospodarsky, G. B., et al. (2020). Analysis of electric and magnetic lightning‐generated wave amplitudes measured by the Van Allen Probes. Geophysical Research Letters, 47, e2020GL087503. https://doi.org/ 10.1029/2020GL087503
Holzworth, R. H., McCarthy, M. P., Brundell, J. B., Jacobson, A. R., & Rodger, C. J. (2019). Global distribution of superbolts. Journal of Geophysical Research: Atmospheres, 124, 9996–10,005, https://agupubs.onlinelibrary.wiley.com/doi/10.1029/JC082i018p02566