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Flickering gamma-ray flashes, the missing link between gamma glows and TGFs

Nature volume 634, pages 53–56 (2024)Cite this article

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Abstract

Two different hard-radiation phenomena are known to originate from thunderclouds: terrestrial gamma-ray flashes (TGFs)1 and gamma-ray glows2. Both involve an avalanche of electrons accelerated to relativistic energies but are otherwise different. Glows are known to last for one to hundreds of seconds, have moderate intensities and originate from quasi-stationary thundercloud fields2,3,4,5. TGFs exhibit high intensities and have characteristic durations of tens to hundreds of microseconds6,7,8,9. TGFs often show a close association with an emission of strong radio signals10,11,12,13,14,15,16,17 and optical pulses18,19,20,21, which indicates the involvement of lightning leaders in their generation. Here we report unique observations of a different phenomenon, which we call flickering gamma-ray flashes (FGFs). FGFs resemble the usual multi-pulse TGFs22,23,24 but have more pulses and each pulse has a longer duration than ordinary TGFs. FGF durations span from 20 to 250 ms, which reaches the lower boundary of the gamma-ray glow duration. FGFs are radio and optically silent, which makes them distinct from normal TGFs. An FGF starts as an ordinary gamma-ray glow, then suddenly increases exponentially in intensity and turns into an unstable, ‘flickering’ mode with a sequence of pulses. FGFs could be the missing link between the gamma-ray glows and conventional TGFs, whose absence has been puzzling the atmospheric electricity community for two decades.

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Fig. 1: Flickering gamma-ray flashes from 05:01:12.44 ut to 05:01:12.64 ut on 8 July 2023.
Fig. 2: 24 FGFs seen by ALOFT.

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Data availability

All the data used in this study are available from Zenodo at https://doi.org/10.5281/zenodo.11930007 (ref. 39). Descriptions of the data formats have been included in the Supplementary Information.

Code availability

References to software tools and codes for this study are given in the file Data_codes_description.pdf, which has been uploaded to Zenodo at https://doi.org/10.5281/zenodo.11930007 (ref. 39).

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Acknowledgements

This work made use of data from UIB-BGO, iSTORM, FEGS, EFCM, low-frequency and VHF sensors, and the Global Lightning Detection Network. The ALOFT campaign and the UIB-BGO instrument were supported by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013, Grant Agreement No. 320839) and the Research Council of Norway (Contract Nos. 223252/F50 (CoE) and 325582). Some of the simulations were performed on resources provided by UNINETT Sigma2, the National Infrastructure for High Performance Computing and Data Storage in Norway (Project No. NN9526K). Work on ALOFT at the US Naval Research Laboratory is supported by the Office of Naval Research 6.1 funds. In addition, D. Shy is supported by the US Naval Research Laboratory’s Jerome and Isabella Karle Fellowship. The FEGS and EFCM team acknowledge the work of S. Podgorny, D. Corredor and M. Stewart. S.C. and Y.P. were partly supported by the National Science Foundation’s Dynamic and Physical Meteorology Program (Grant No. AGS-2026304). The use of the VHF data was supported by the US National Science Foundation (Grant Nos. 1720600 and 2214044). A. Freeman, R. Bernath, A. Lamoureux and R. Brown of the University of Central Florida assisted with the deployment and maintenance of the VHF interferometer at the Townes Institute Science and Technology Experimentation Facility. The participation of J.A.R., J.L., M.U., O.v.d.V. and J.M. and the fielding of instruments on San Andrés island were supported by the government of Spain (Projects EQC2021-006957-P and PID2022-136348NB-C33 and Grant No. MCIN/AEI/10.13039/501100011033) and the European Regional Development Fund ‘ERDF—A way of making Europe’ by the European Union. M.F. was sponsored by the Royal Society, UK (Grant No. NMG/R1/180252) and the Natural Environment Research Council, UK (Grant Nos. NE/L012669/1 and NE/H024921/1). Significant financial and logistical support for ALOFT was provided by the NASA Earth Science Division. We thank the governments of Mexico, the Bahamas, Colombia, Belize, Guatemala, Honduras, Nicaragua, Panama, the Dominican Republic, Costa Rica, El Salvador, Haiti, Turks & Caicos, Jamaica and the Cayman Islands for approving ER-2 overflights in support of ALOFT. Geostationary Operational Environmental Satellites Mesoscale Domain Sectors in support of ALOFT were enabled by the National Oceanic and Atmospheric Administration. We thank the ER-2 Project Team at NASA Armstrong Flight Research Center and the MacDill Air Force Base for acting as hosts.

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Authors and Affiliations

  1. Department of Physics and Technology, University of Bergen, Bergen, Norway

    N. Østgaard, A. Mezentsev, M. Marisaldi, D. Sarria, N. Lehtinen, K. Ullaland, S. Yang, B. Hasan Qureshi, J. Søndergaard & B. Husa

  2. Astrophysics and Space Science Observatory, National Institute for Astrophysics, Bologna, Italy

    M. Marisaldi

  3. US Naval Research Laboratory, Washington, DC, USA

    J. E. Grove & D. Shy

  4. NASA Marshall Space Flight Center, Huntsville, AL, USA

    M. Quick, T. Lang, C. Schultz & R. Blakeslee

  5. Department of Atmospheric Science, Earth System Science Center, University of Alabama in Huntsville, Huntsville, AL, USA

    H. Christian, D. Walker, M. Bateman & P. Bitzer

  6. Duke University, Durham, NC, USA

    S. Cummer & Y. Pu

  7. Instituto de Ciencias de la Atmosfera y Cambio Climático, UNAM, Mexico City, Mexico

    M. Pazos

  8. New Mexico Institute of Mining and Technology, Socorro, NM, USA

    M. Stanley & P. Krehbiel

  9. NASA Goddard Space Flight Center, Greenbelt, MD, USA

    I. Adams, R. Kroodsma & G. Heymsfield

  10. University of Bath, Bath, UK

    M. Fullekrug

  11. Georgia Institute of Technology, Atlanta, GA, USA

    M. Cohen

  12. Polytechnic University of Catalonia, Barcelona, Spain

    J. Montanya, O. van der Velde, J. A. Roncancio, J. A. Lopez & M. Urbani

  13. Universidad Nacional de Colombia, Bogota, Colombia

    C. Younes & A. Santos

  14. Universities Space Research Association, Huntsville, AL, USA

    D. Mach

Authors
  1. N. Østgaard
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Contributions

N.O. and A.M. led this study. The ALOFT campaign was led by N.O., T.L. M.M. and C.S. The UIB-BGO instrument was provided by N.O., M.M., K.U., S.Y. B.H.Q., J.S. and B.H. and analysed by N.O., M.M., D. Sarria and N.L. The iSTORM data were provided and analysed by J.E.G., D. Shy and D.W. The FEGS data were provided by M.Q. and the EFCM data were provided by H.C. and R.B. Radio data used in this study were provided and analysed by S.C., Y.P. and M.P. and other low-frequency stations were operated by P.B., M.F., M.C., J.M., C.Y., O.v.d.V. J.A.R., J.A.L., M.U. and A.S. The VHF data were provided and analysed by M.S. and P.K. Radar and electric-field data for the entire campaign were provided by I.A., R.K., G.H., R.B., M.B. and D.M.

Corresponding authors

Correspondence to N. Østgaard, A. Mezentsev or M. Marisaldi.

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Extended data figures and tables

Extended Data Fig. 1 Three FGF events with EFCM recordings.

Black lines show FGF light curves of the FGFs, while red lines represent electric field variability as recorded by EFCM. The last pulse of the FGF is marked with a red arrow and the following NBE with a black arrow.

Extended Data Fig. 2 LF signal power during the time window of two FGF events.

Overlaid are the data-derived peak power of lightning pulses at the observed distance for a range of peak currents. For the 2023/07/08 05:01:12 UTC FGF (panel A), the noise level and 922 km distance imply that any current pulses associated with the FGF must be lower than 1 kA equivalent. For the 2023/07/29 21:03:19 UTC FGF (panel B), the noise level and much shorter 75 km distance that any current pulses associated with the FGF must be at least 10 times smaller than 1 kA.

Extended Data Fig. 3 VHF and FA signals during the FGF on July 29, 2023.

A): A 200-millisecond interval of VHF source azimuths with fast antenna data (green) and raw VHF data (cyan). Sources are color-coded according to VHF power ranging from dark blue (weakest) to bright red (strongest). The azimuth location of the ER-2 is marked with a dashed line. B): The BGO data in 100 microsecond bins.

Extended Data Fig. 4 Optical measurements for 22 of the 24 FGFs.

Black and blue curves are the FGFs with bins of cnts/ms and cnts/100μs, respectively. The accumulated optical signals are shown in red (777.4 nm emissions) and blue (337.1 nm emissions). For event #20 and #21 the FEGS instrument was not working. The values in the upper right corner (in red) are the time interval in millisecond shown in each plot. The numbering in the upper left corner is the event ID, which corresponds to dates and times of each event that are given in Extended Data Table 5.

Extended Data Fig. 5 Spectral measurements and fits for two bright FGFs.

A) #2 B) #9. Negative log-likelihood (NLL) values for the spectral fits are given in Extended Data Table 6.

Extended Data Table 1 Specification for the UIB-BGO detectors
Full size table
Extended Data Table 2 Specification for the iSTORM detectors
Full size table
Extended Data Table 3 Specification for FEGS
Full size table
Extended Data Table 4 Specification for EFCM
Full size table
Extended Data Table 5 Date, time and ER-2 location for the 24 FGF events
Full size table
Extended Data Table 6 Parameters for the spectral fit in Extended Data Fig. 5
Full size table
Extended Data Table 7 Estimated maximum peak flux of saturated pulses
Full size table

Supplementary information

Supplementary Data and Codes

Data and codes used in the study.

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Østgaard, N., Mezentsev, A., Marisaldi, M. et al. Flickering gamma-ray flashes, the missing link between gamma glows and TGFs. Nature 634, 53–56 (2024). https://doi.org/10.1038/s41586-024-07893-0

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