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Interferometric imaging of intensely radiating negative leaders

O. Scholten, B. M. Hare, J. Dwyer, N. Liu, C. Sterpka, I. Kolmašová, O. Santolík, R. Lán, L. Uhlíř, S. Buitink, T. Huege, A. Nelles, and S. ter Veen
Phys. Rev. D 105, 062007 – Published 25 March 2022
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  • INTRODUCTION
  • METHODS
  • DATA ANALYSIS
  • SUMMARY AND DISCUSSION
  • ACKNOWLEDGMENTS
  • APPENDICES
    • References

    Abstract

    The common phenomenon of lightning still harbors many secrets and only recently a new propagation mode was observed for negative leaders. While propagating in this “intensely radiating negative leader” (IRNL) mode a negative leader emits 100 times more very-high frequency (VHF) and broadband radiation than a more normal negative leader. We have reported that this mode occurs soon after initiation of all lightning flashes we have mapped as well as sometimes long thereafter. Because of the profuse emission of VHF the leader structure is very difficult to image. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily built for radio-astronomy observations. For this reason, as part of the present work, we have refined our time resolved interferometric 3-dimensional (TRI-D) imaging to take into account the antenna function. The images from the TRI-D imager show that during an IRNL there is an ionization front with a diameter in excess of 500 m where strong corona bursts occur. This is very different from what is seen for a normal negative leader where the corona bursts happen at the tip, an area of typically 10 m in diameter. The observed massive ionization wave supports the idea that this mode is indicative of a dense charge pocket.

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    • Received 7 October 2021
    • Accepted 22 February 2022

    DOI:https://doi.org/10.1103/PhysRevD.105.062007

    © 2022 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Atmospheric science
    Nonlinear DynamicsInterdisciplinary PhysicsGeneral Physics

    Authors & Affiliations

    O. Scholten1,2,3, B. M. Hare1, J. Dwyer4, N. Liu4, C. Sterpka4, I. Kolmašová5,6, O. Santolík5,6, R. Lán5, L. Uhlíř5, S. Buitink7,8, T. Huege9,8, A. Nelles10,11, and S. ter Veen12

    • 1University Groningen, Kapteyn Astronomical Institute, Landleven 12, 9747 AD Groningen, Netherlands
    • 2University of Groningen, KVI Center for Advanced Radiation Technology, 9747 AA Groningen, Netherlands
    • 3Interuniversity Institute for High-Energy, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
    • 4Department of Physics and Astronomy, University of New Hampshire, Durham, New Hampshire 03824, USA
    • 5Department of Space Physics, Institute of Atmospheric Physics of the Czech Academy of Sciences, 141 00 Prague, Czech Republic
    • 6Faculty of Mathematics and Physics, Charles University, 121 16 Prague, Czech Republic
    • 7Department of Astrophysics/IMAPP, Radboud University Nijmegen, 6525 AJ Nijmegen, Netherlands
    • 8Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
    • 9Institute for Astroparticle Physics, Karlsruhe Institute of Technology(KIT), P.O. Box 3640, 76021 Karlsruhe, Germany
    • 10Erlangen Center for Astroparticle Physics, Friedrich-Alexander-Univeristät Erlangen-Nürnberg, 91058 Erlangen, Germany
    • 11DESY, Platanenallee 6, 15738 Zeuthen, Germany
    • 12Netherlands Institute for Radio Astronomy (ASTRON), 7991 PD Dwingeloo, Netherlands

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    Issue

    Vol. 105, Iss. 6 — 15 March 2022

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    Images

    • Figure 1
      Figure 1

      TRI-D image for a simulation with a cloud of point sources as discussed in the text. The topmost panel shows the time trace. The panels below show different projections of the imaged sources.

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    • Figure 2
      Figure 2

      Image made with the impulsive imager of the first 15 milliseconds of flash A. The topmost panel shows the recorded signal in the broadband antenna, rebinned over 0.2  μs. The lime-green (cyan) colored rectangles indicate the tesseract (4 dimensional cube) imaged with TRI-D and displayed in Fig. 3 (Fig. 4) respectively.

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    • Figure 3
      Figure 3

      The left two panels show two TRI-D images of the initial part of the first IRNL seen in flash A (see Fig. 2, lime-green colored tesseract). For comparison the TRI-D image of a normal negative leader, propagating over a distance of about 0.5 km in 5 ms, is shown on the right. The broadband time trace is not shown as at this time period there are several other leaders propagating.

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    • Figure 4
      Figure 4

      Northern filament that emerges from the first IRNL (see Fig. 2). The black dots label the most recent 0.1 ms strong sources, the arrows the two starting negative leaders.

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    • Figure 5
      Figure 5

      An enlargement of the section around t=276  ms of flash B where strong signals were measured in the broadband antenna as shown in the top panel. The lime-green colored rectangles give the projections of the tesseract used for imaging the IRNL in Fig. 6, the plum colored ones that for the normal negative leader of Fig. 6. The yellow and cyan arcs show where the IRNL mode stops and negative leaders start to emerge.

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    • Figure 6
      Figure 6

      The TRI-D image of the early part of the IRNL for flash B is shown on the left. The imaged area is shown by the lime-green-colored tesseract in Fig. 5. The TRI-D image of a normal negative leader (indicated by the plum-colored tesseract in Fig. 5) is shown on the right to show the contrast. Note that the right-hand panels have a significantly smaller spatial scale than the left-hand panels.

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