After having published the first thunderstorm ground enhancements (TGEs) catalog to explain long-lasting TGEs, we address here problems pertaining to TGE evolution (shape) and atmospheric conditions ...supporting the origination of the relativistic runaway electron avalanches. We also address the question of radon progeny gamma radiation and its contribution to overall TGE flux. We demonstrate that by using detectors with different energy thresholds we can identify and reliably separate both mechanisms of TGE origination. An analysis of measured energy spectra of TGEs reveals contributions of both processes to the TGE temporal evolution and shape. We also confirm the model of radon progeny radiation during a thunderstorm.
Abstract
The shape and evolution of the energy spectra of the
thunderstorm ground enhancement (TGE) electrons and gamma rays shed
light on the origin of TGEs, on the relationship between
modification ...of the cosmic ray electron energy spectra (MOS) and
relativistic runaway electron avalanche (RREA) processes, on the
energy of the seed electrons, and on the strength and elongation of
an atmospheric electric field. The network of large NaI
spectrometers on slopes of Mt. Aragats 24/7 monitored secondary
particle fluxes from 2013 until now, highly contributed to the
understanding of the ways how RREAs are developed in the
atmosphere. In 2022 we enlarge the NaI network with 2 remote
detectors located at altitudes 2000 and 1700 m, and 13 and 16 km
apart from the Aragats station to investigate the horizontal profile
of the atmospheric electric field. We found, that the previously
estimated values of the regions in the atmosphere, where RREA
emerges, were highly underestimated. In the present report, we
describe the NaI particle detector's network and present the first
results of the experiment demonstrating that the particle fluxes
from the atmospheric electron accelerators can cover large areas on
the earth's (up to tens of km
2
).
To identify the role of the gamma radiation from radon progenies in long-lasting thunderstorm ground enhancement (TGE) flux, the differential energy spectrum is measured with various spectrometers, ...including precise spectrometer of ORTEC firm built with 3"×3" inches sodium iodide NaI(Tl) crystal; full width at half maximum (FWHM) ∼7.7% at 0.6 MeV. The measurements demonstrate that radon progeny radiation significantly contributes to the count rate enhancements measured in the winter of 2018–2019 in the energy range below 3 MeV. However, performed Monte Carlo simulations and observation of long-lasting TGEs with plastic scintillators of various thicknesses and energy thresholds show that TGEs originate in the intracloud electric fields. Radon progenies (mostly Bi214 spectral lines) contribute to count rate in the low-energy domain.
Natural gamma radiation (NGR), one of the major geophysical parameters directly connected with cloud electrification and lightning initiation, is highly enhanced during thunderstorms. At low energies ...below 3 MeV, the enhancement of NGR is due to natural isotope radiation, and for energies up to 50 MeV, it is due to the operation of the newly discovered electron accelerators in the thunderclouds. For the first time, we present a comprehensive model of the enhanced fluxes of radiation incident on the earth's surface during thunderstorms. In addition to the already explained minute-long fluxes of high-energy electrons and gamma rays from relativistic runaway electron avalanches (RREA), we clarify also the origin of hour-long isotropic fluxes of low-energy gamma rays from the Rn-222 progenies. Also, as a direct evidence of RREA, we present photographs of optical emission during the development of electron-gamma ray cascades in the atmosphere. Natural radioactivity is a source of continuous exposure of human beings to radiation. Radiation protection of living organisms requires an understanding of all sources and possible ways of enhancement of the radiation levels that can double for several hours in the energy domain of hundreds of keV. Therefore individual irradiation doses can be exceeded during thunderstorms. The models used for the forecasting of thunderstorms and other severe atmospheric phenomena need an accurate account of the ionizing radiation in the atmosphere. The airglows can influence the operation of optical, fluorescence, and atmospheric Cherenkov telescopes and fluorescence detectors.
In 2011, a network of five thallium-doped sodium iodide (Nal(Tl)) detectors was installed on Aragats Space Environmental Center (ASEC) and was included into ASEC detectors system. Along with ...monitoring of different species of secondary cosmic rays, ASEC detectors register several thunderstorm ground enhancements (TGEs). NaI(Tl) detector integration in the ASEC detector system is of great importance for the study of thunderstorm phenomena for the reason that NaI(Tl) detectors have a higher efficiency of gamma rays detection compared with plastic ones. In this article, the design and characteristics of NaI(Tl) detectors are described. Simulations of detector response are performed. Comparison of simulation results with experimental data showed good agreement between simulations and experimentally observed distributions for analog-to-digital converter (ADC) channels (codes) of NaI(Tl) detectors at two depths of the atmosphere, thus, indicating the correctness of the detector׳s response determination. A procedure for reconstruction of gamma energy spectrum was developed and approximation of the energy spectrum of recorded TGE event was carried out by a power function under the assumption that the recorded fluxes consist mainly of gamma quanta.
An unprecedented thunderstorm ground enhancement (TGE) event was recorded on May 23, 2023, at Aragats Mountain, the highest peak in Armenia. This event showcased a maximum flux intensity surpassing 3 ...million particles per minute per square meter for energies above 0.4 MeV. Distinctly, the fluence of the event was measured at approximately ≈700 particles/cm2. The comprehensive instrumentation at the Aragats research station, including a suite of spectrometers and detectors, enabled precise cross-correlation of measurements. The electron flux at energies exceeding 10 MeV was observed at roughly ≈55,000 particles per minute per square meter. Additional measurements, including cloud base heights and corona discharge detections, validated the intensity of the electric field, reaching approximately 2.1 kV/cm at elevations 50–100 m above ground level. Our observations confirm that TGE is a universal and significant atmospheric event, contributing a substantial flux of high-energy electrons to the global electrical circuit. Integrating such TGE phenomena into Earth's numerical models is imperative, considering their impact on aviation and aerospace operation safety.
The Aragats Space-Environmental Center provides monitoring of different species of secondary cosmic rays at two altitudes and with different energy thresholds. One-minute data is available on-line ...from
http://crdlx5.yerphi.am/DVIN/index2.php. We present description of the main monitors along with data acquisition electronics. Also we demonstrate the sensitivity of the different species of secondary cosmic ray flux to geophysical conditions, taking as examples the extremely violent events of October–November 2003. We introduce correlation analysis of the different components of registered time-series as a new tool for the classification of the geoeffective (events on earth affected by solar activity) events and for the forecasting of the severity of the upcoming geomagnetic storm.
For lightning research, we monitor particle fluxes from thunderclouds, the so-called thunderstorm ground enhancements (TGEs) initiated by runaway electrons, and extensive air showers (EASs) ...originating from high-energy protons or fully stripped nuclei that enter the Earth's atmosphere. We also monitor the near-surface electric field and atmospheric discharges using a network of electric field mills.
The Aragats “electron accelerator” produced several TGEs and lightning events in the spring of 2015. Using 1-s time series, we investigated the relationship between lightning and particle fluxes. Lightning flashes often terminated the particle flux; in particular, during some TGEs, lightning events would terminate the particle flux thrice after successive recovery. It was postulated that a lightning terminates a particle flux mostly in the beginning of a TGE or in its decay phase; however, we observed two events (19 October 2013 and 20 April 2015) when the huge particle flux was terminated just at the peak of its development. We discuss the possibility of a huge EAS facilitating lightning leader to find its path to the ground.
The shape and evolution of the energy spectra of the thunderstorm ground enhancement (TGE) electrons and gamma rays shed light on the origin of TGEs, on the relationship of modification of the energy ...spectra (MOS) and relativistic runaway electron avalanche processes, on the nature of the seed particles, and on the strength and elongation of an atmospheric electric field. However, till now the measurements of energy spectra of TGE electrons and gamma rays have been rather scarce. For the first time, we present differential energy spectra of gamma rays in the wide energy range 4-100 MeV for five TGE events detected in 2012-2013 at Aragats. We use the special technique of electron/gamma ray fraction determination to select TGE events with very small contamination of electrons. The network of large Nal spectrometers located 3200 m above sea level measured energy spectra of gamma rays. The power law indices of "small" TGEs are rather close to the background cosmic gamma ray spectrum ( gamma ~ -2); thus, we may deduce that these small events are due to MOS of cosmic ray electrons in the electric field of a thundercloud. Larger TGEs measured by the Nal network and the two largest TGE events earlier recovered from energy releases in a 60-cm-thick scintillator have much steeper energy spectra typical for the avalanche process in atmosphere. The classification of TGEs according to intensity and gamma ray spectral index pointed toward two main mechanisms of the TGE gamma ray origin: the runaway process and modification of electron energy spectra in the thunderstorm atmospheres.
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