01 Apr 2022
01 Apr 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Continental Thunderstorm Ground Enhancement observed at an exceptionally low altitude

Ivana Kolmašová1,2, Ondřej Santolík1,2, Jakub Šlegl3,4, Jana Popová1, Zbyněk Sokol1, Petr Zacharov1, Ondřej Ploc3, Gerhard Diendorfer5, Ronald Langer6,3, Radek Lán1, and Igor Strhárský6 Ivana Kolmašová et al.
  • 1Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czechia
  • 2Faculty of Mathematics and Physics, Charles University, Prague, Czechia
  • 3Nuclear Physics Institute of the Czech Academy of Sciences, Husinec‑Rez, Czechia
  • 4Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czechia
  • 5Department of ALDIS, OVE Service GmbH, Vienna, Austria
  • 6Institute of Experimental Physics, Slovak Academy of Sciences, Kosice, Slovakia

Abstract. Two long-lasting Thunderstorm Ground Enhancement (TGE) events were registered at the Milešovka meteorological observatory in Czechia (50.55N, 13.93E, altitude 837 m) on 23 April 2018, during linearly organized thunderstorms. Two intervals of increased photon counts were detected by a plastic scintillator, respectively lasting 70 and 25 minutes, and reaching 31 % and 48 % above the background radiation levels. Using numerical simulations, we verified that the observed increases of count rates are consistent with the energy spectrum of previously observed TGEs. We investigated the relevant data from a suite of meteorological instruments, a Ka-band cloud radar, an electric field mill, and a broadband electromagnetic receiver, all placed at the Milešovka observatory, in order to analyze the context in which these unique continental TGEs occurred at an exceptionally low altitude. The onset of the TGEs preceded the onset of precipitation by 10 and 3 minutes, respectively, for the two events. Both this delayed rain arrival and a lower energy threshold of 6.5 MeV for registered particles clearly exclude the detection the decay products of the radon progeny washout during the TGE intervals. At the same time, the European lightning detection network EUCLID detected numerous predominantly negative intracloud lightning discharges at distances closer than 5 km from the particle detector, while the occurrence of cloud-to-ground discharges was suppressed. The cloud radar recorded presence of graupel below the melting level and the composition of hydrometeors suggested good conditions for cloud electrification. The observed variations of the near surface electric field were unusual, with very brief negative electric field excursions reaching -20 kV in a quick succession. At the same time, sub-microsecond unipolar pulses emitted by close corona discharges saturated the broadband magnetic loop antenna. All these measurements indicate that a strong lower positive charge region was present inside the thundercloud. The bottom thundercloud dipole was probably responsible for acceleration of the seed electrons in the air. These seed electrons might originate not only in the secondary cosmic ray particles but could also come from a high concentration of radon in the air collected during the propagation of the convective system above the uranium-rich soils before the thunderstorms overpassed the Milešovka observatory.

Ivana Kolmašová et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-125', Ashot Chilingarian, 05 Apr 2022
    • AC1: 'Reply on RC1', Ivana Kolmasova, 21 Apr 2022
      • RC2: 'Reply on AC1', Ashot Chilingarian, 21 Apr 2022
  • EC1: 'Comment on acp-2022-125', Heini Wernli, 21 Apr 2022
  • RC3: 'Comment on acp-2022-125', Martino Marisaldi, 06 May 2022
    • AC2: 'Reply on RC3', Ivana Kolmasova, 21 May 2022

Ivana Kolmašová et al.

Ivana Kolmašová et al.


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Short summary
Gamma ray radiation related to thunderstorms was previously observed at the high-altitude mountain observatories or on the western coast of Japan, being usually terminated by lightning discharges. We show unusual observations of gamma rays at an altitude below 1000 m, coinciding with peculiar rapid variations of the vertical electric field, which are linked to inverted intracloud lightning discharges. This indicates that a strong lower positive charge region was present inside the thundercloud.