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A terrestrial gamma-ray flash and ionospheric ultraviolet emissions powered by lightning

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Science  10 Jan 2020:
Vol. 367, Issue 6474, pp. 183-186
DOI: 10.1126/science.aax3872
  • Fig. 1 Location of the TGF event observed on 10 October 2018.

    (A) Cloud top altitudes (15) are shown according to the color scale to the right of (B). The yellow curve shows the ISS orbit; the red dot marks its position at the onset time of the TGF at 13:01:33.100080 UTC. The white dot marks the most probable TGF location, with white contours outlining the 68% and 95.4% confidence regions. The black curves outline the southern limit of the full field of view of the optical instruments, the white dash-lined box outlines the cropped segment of the image downlinked from the ISS, and the red cross is the location of a coincident lightning event detected by WWLLN (15). (B) The same view zoomed in to the active cloud region. A single thundercloud partially overlaps with the TGF 95% confidence region. (C) The TGF position overlain with a projection of the ASIM camera image in the 337-nm filter; exposure time, 83 ms. The attitude of the ASIM instruments is calibrated to align the WWLLN lightning location with the maximum optical activity of the ASIM image.

  • Fig. 2 Light curves of the event.

    The gamma-flash trigger time is at t = 0, which corresponds to 13:01:33.100080 UTC. (A) Photometer (left axis) and x-ray and gamma-ray (right axis) measurements around the time of the event. LED is the low-energy x-ray detector (50 to 350 keV) and HED the high-energy detector (300 keV to 30 MeV). The UV photometer measures 180 to 235 nm and is multiplied by 100 to show on the same scale as the optical photometers. All three photometers sample at 100 kHz. (B) The same data shown zoomed in further at the time of the TGF.

  • Fig. 3 Our proposed scenario.

    An intra-cloud (IC) lightning event generates a TGF and electromagnetic pulse (EMP). The EMP excites expanding waves of UV emission in the lower ionosphere (elve). TGF and UV emissions are observed by ASIM on the ISS (arrows).

  • Fig. 4 Analysis of the lightning flash.

    (A) The same data as Fig. 2 but on a logarithmic scale and smoothed by a Gaussian filter with width σ = 10 samples. Two additional optical pulses occur 200 to 300 ms after the initial flash. (B) The same data zoomed in to the start of the flash smoothed with σ = 2 samples. Optical emission begins 5 ms prior to UV emission and the TGF.

Supplementary Materials

  • A terrestrial gamma-ray flash and ionospheric ultraviolet emissions powered by lightning

    Torsten Neubert, Nikolai Østgaard, Victor Reglero, Olivier Chanrion, Matthias Heumesser, Krystallia Dimitriadou, Freddy Christiansen, Carl Budtz-Jørgensen, Irfan Kuvvetli, Ib Lundgaard Rasmussen, Andrey Mezentsev, Martino Marisaldi, Kjetil Ullaland, Georgi Genov, Shiming Yang, Pavlo Kochkin, Javier Navarro-Gonzalez, Paul H. Connell, Chris J. Eyles

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Fig. S1
    • Captions for Data S1 to S5
    • References
    Data S1
    ASIM Photometer Data
    The first column is the time of start of the 10-μs photometer samples and the following columns the radiances measured by the 337 nm, UV, 777 nm photometers in in microwatt per square meter (μWm-2).
    Data S2
    ASIM 337 nm Camera Data
    The first and second column give the column and row indices of the 337 nm CCD camera pixels, the 3rd and 4th columns give the longitude and latitude of the corresponding ground projection assuming a source altitude of 12 km and a World Geodetic System 1984. The 5th column gives the pixel radiances (μW m-2 sr-1). The image integration started at 13:01:33.043 UTC and ended at 13:01:33.126 UTC.
    Data S3
    ASIM LED Data
    Time in UTC is given of each photon detected in the LED. Only photons that correspond to energies above ADC channel 140 (70 keV) are included. To reproduce the histograms in Fig. 2, one needs to start the 10 μs-binning from13:01:33.10008 UTC.
    Data S4
    ASIM LED Imaging Data
    The two first columns give the longitude and latitude of the corresponding ground projection assuming a source altitude of 12 km and a World Geodetic System 1984. The last column gives the maximum likelihood for the arrival direction of photons from an assumed point source, using information on the coded mask in front of the pixelated sensors (14).
    Data S5
    ASIM HED Data
    Time in UTC is given of each photon detected in the HED. All ADC channels are included, which corresponds to >300 keV gamma photons. To reproduce the histograms in Fig. 2 one needs to start the 10 μs-binning from 13:01:33.10008 UTC.

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