Abstract
High electric fields that occur in thunderstorm clouds in the Earth’s atmosphere might accelerate energetic charged particles produced by cosmic rays. Such energetic particles, especially electrons, can cause additional ionization as they are multiplied and thus form avalanche of relativistic electrons. These relativistic electrons emit Bremsstrahlung in the X- or gamma-ray spectral ranges as they lose their kinetic energy via collisions. Thunderstorm ground enhancements (TGEs) of secondary cosmic ray fluxes recorded at the top of a sharp rocky mountain of Lomnický Štít in High Tatras (2634 m, Slovak Republic) are compared with simultaneous measurements of electric field at the mountain top and on its slope at the observatory of Skalnaté Pleso (1780 m). Results of measurements performed from May to September in 2017 and from May to October in 2018 are presented. The cosmic ray flux is measured by Space Environment Viewing and Analysis Network (SEVAN) and by neutron monitor with 1-s resolution. The TGEs that persisted usually several minutes were mainly detected in the SEVAN channel 1 which has the lowest energy threshold, about 7–8 MeV. A statistical analysis shows that these enhancements usually occurred (not only) during large values of vertical, upward-pointing electric fields measured just above the detector. It is shown that the measurement of electric field at Skalnaté Pleso, distant about 1.86 km from the mountain top is also partly correlated with the enhancements and can provide additional useful information about the distance or dimension of charge structure and dynamics of electric field, especially on short time scales. The enhancements usually did not exceed several tens of percent of background values. However, events that exceeded the background values several times were also recorded. The most extreme event exceeded the background values about 215 times. This event was also detected by other SEVAN channels and by the neutron monitor (~ 130% enhancement), which indicates a possibility of photonuclear reactions. The enhancements were often terminated by a nearby lightning.
Highlights
There are two distinct energetic phenomena in the Earth’s atmosphere that generate gamma-rays during thunderstorms: terrestrial gamma-ray flashes (TGFs) andChum et al Earth, Planets and Space (2020) 72:28 glows—often called thunderstorm ground enhancements (TGEs), if observed on the ground (Chilingarian and Mkrtchyan 2012)—are less intense emissions of much longer duration, usually of several minutes
It was shown that the enhancements of secondary cosmic ray flux (TGEs) represented by increases of Nres in Space Environment Viewing and Analysis Network (SEVAN) channel 1 usually occurred during large values of upward-pointing electric field, which means that electrons were accelerated downward
The TGEs were usually () recorded at times when large upward electric fields were measured at the same location
Summary
There are two distinct energetic phenomena in the Earth’s atmosphere that generate gamma-rays during thunderstorms: terrestrial gamma-ray flashes (TGFs) and. The discharge was detected by electric field measurement as a relatively large sudden increase—upward step of PG recorded both at LS and SP (Fig. 4b) at the time of the TGE termination. The peak values in SEVAN channel 1 exceeded the background values about 215 times Several strokes of this complicated discharge were located by EUCLID to the summit of LS (observatory) or to its close vicinity (Fig. 10c).
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