First observation of significant long-lasting Thunderstorm Ground Enhancements on the Milešovka peak (altitude 837 m) in Czechia

0542842 - ÚFA 2022 DE eng A - Abstrakt
Kolmašová, Ivana - Santolík, Ondřej - Ploc, Ondřej - Langer, Ronald - Popová, Jana - Sokol, Zbyněk - Zacharov, Petr, jr. - Šlegl, Jakub - Diendorfer, G. - Strhárský, I. - Lán, Radek - Kákona, Martin
First observation of significant long-lasting Thunderstorm Ground Enhancements on the Milešovka peak (altitude 837 m) in Czechia.
EGU General Assembly 2021 (vEGU21: Gather Online). Göttingen: European Geosciences Union, 2021.
[EGU General Assembly Conference 2021. 19.04.2021-30.04.2021, online]
Institucionální podpora: RVO:68378289 ; RVO:61389005
Klíčová slova: cosmic rays * particle detector SEVAN * Thunderstorm Ground Enhancements (TGE) * thunderstorm clouds
Obor OECD: Fluids and plasma physics (including surface physics); Fluids and plasma physics (including surface physics) (UJF-V)
https://meetingorganizer.copernicus.org/EGU21/EGU21-3141.html

Bursts of gamma rays observed on the Earth’s surface – so called Thunderstorm Ground
Enhancements (TGE) were detected by a plastic scintillator (disassembled from the particle
detector SEVAN) located in the observatory building on the Milešovka peak (50.6N, 13.9E, altitude
837 m) in Czechia. The TGEs observed during two thunderstorms on 23 April 2018 respectively
lasted 65 and 15 minutes and exceeded the background radiation levels by 30 and 40 percent.
The first storm was a part of an evolving squall line which crossed the Milešovka peak. The second
storm was probably a supercell, which moved near Milešovka but did not hit its top. Both storms
caused heavy precipitation and strong wind gusts. The onset of the TGEs preceded the onset of
precipitation by approximately 8 minutes. During the increases of TGE radiation, the European
lightning detection network EUCLID detected numerous predominantly negative intracloud
lightning discharges at distances closer than 5 km from the particle detector.
To understand the conditions for the TGE observation we investigated the data collected during
the enhancements by a Ka-band cloud radar, an electric field mill, and a broadband
electromagnetic receiver installed in the Milešovka peak observatory. Using the cloud radar
measurements, we estimated the vertical extent of the thunderclouds. The cloud base was found
at about 500 m above the observatory. Estimated heights of the cloud tops for the two storms
were 12 and 8 km, respectively, indicating that the storm center of the second storm was not
directly above the cloud radar. The updraft velocities reached 10 m/s. A composition of
hydrometeors suggested good conditions for cloud electrification.
We have found that the increases of TGE radiation corresponded to the large negative electric
fields (up to – 20 kV/m) measured by the electric field mill rather than to individual discharges. We
also identified numerous microsecond-scale pulses in the broadband magnetic field records,
which can be attributed to corona-type discharges occurring near the receiving antenna in high
local electric fields below the thunderstorm.
Based on our analysis we assume that observed TGEs corresponded to the bremsstrahlung
generated during collisions of electrons accelerated in the thunderstorm electric field with the air
molecules. Because of a very small number of cloud-to-ground lighting discharges we hypothesize
that the electrons might have been accelerated by a strong lower positive charge center at the
bottom of the thundercloud. As the TGE radiation increases were unusually long, we speculate
that their later part might have been assigned to the radon progeny which was lifted to the
atmosphere by a near-surface electric field and returned back to the ground with the rain
precipitation
Trvalý link: http://hdl.handle.net/11104/0320192