Thunderstorm Atmosphere Research Articles

Preliminary Results of Searches for Long-Term Microwave Radiation of a Thunderstorm Atmosphere at a Wavelength of 1.35 cm

Preliminary Results of Searches for Long-Term Microwave Radiation of a Thunderstorm Atmosphere at a Wavelength of 1.35 cm

Relativistic runaway electron avalanche

Discussed are the genesis of the concept of the relativistic runaway electron avalanche (RREA) and its mechanism as an analog of the Townsend’s avalanche, but capable of developing, unlike the latter, in weak thundercloud electric fields. Thanks to this, it was possible to overcome difficulties while interpreting results of observations of penetrating emission enhancements in thunderstorm atmospheres. The main inelastic interactions of high-energy electrons with atomic particles participating in the avalanche development are described; in terms of the drag forces, the essence of the runaway process is discussed; and methods of RREA numerical simulation are described. In approximate historical sequence, results of calculations of the spatial and temporal scales of the avalanche enhancement are analyzed and contemporary data on avalanche macroscopic characteristics are given, which is required for numerical simulations of the runaway electrons in the fluid approximation. As an extension to the relativistic range of the mechanism of the classical cathode-directed streamer, relativistic positive feedback is discussed, by means of which a generation of the RREA series, as a self-sustained process, is supported. Laboratory experiments on RREA modeling are described, in one of which the initial stage of the avalanche was produced. The historical background of the issue is often more interesting than the results obtained. I P Pavlov (1849–1936), 1904 Nobel Prize winner in Physiology and Medicine

Fluorescence Excited in a Thunderstorm Atmosphere by Relativistic Runaway Electron Avalanches

Fluorescence Excited in a Thunderstorm Atmosphere by Relativistic Runaway Electron Avalanches

Autonomous station for recording radiation in a thunderstorm atmosphere at the Tien Shan high mountain cosmic-ray station

During the past decades, considerable attention has been paid to the search and registration of electromagnetic radiation accompanying lightning discharges in the atmosphere when studying processes occurring in thunderclouds. Such studies are of interest for understanding the mechanisms of lightning generation and its further development, leading to the generation of an avalanche of charged particles accelerated by an electric field, the hard bremsstrahlung of which is registered by the detectors. In this work we consider a compact measuring system, which was created at the Tien Shan High-Mountain Scientific Station for registering radiation during thunderstorm activity. A feature of the system is complete autonomy, when all its components (detectors, recording electronics, battery) are placed inside a solid metal casing, which plays the role of an electromagnetic screen and does not have any connections to external cable lines. This allows one to record radiation directly inside the thundercloud. Examples of gamma-radiation detection using a NaI crystal scintillation detector, as well as the detection of charged particles by a special detector, which is a stack of two flat scintillation detectors of a large area and a rubber filter placed between them, are considered.

The critical avalanche of runaway electrons

The x-ray and gamma-ray flashes observed in the Earth atmosphere during a thunderstorm are usually associated with the generation of runaway electrons (RE) in atmospheric electric fields. It is supposed that runaway electron avalanches initiated by cosmic rays play the main role in high-altitude discharges observed in a thunderstorm atmosphere. We have performed three-dimensional numerical calculations to investigate the mechanism of the development of a critical avalanche and to determine its parameters. It has been shown that the number of electrons in a critical avalanche occurring in air under conditions characteristic of thunderstorm discharges can reach a value of the order of 1018.

The SEVAN Worldwide network of particle detectors: 10 years of operation

The Space Environment Viewing and Analysis Network (SEVAN) aims to improve the fundamental research on particle acceleration in the vicinity of the sun, on space weather effects and on high-energy physics in the atmosphere and lightning initiation. This new type of a particle detector setup simultaneously measures fluxes of most species of secondary cosmic rays, thus being a powerful integrated device for exploration of solar modulation effects and electron acceleration in the thunderstorm atmosphere. The SEVAN modules are operating at the Aragats Space Environmental Center (ASEC) in Armenia, in Croatia, Bulgaria, Slovakia, the Czech Republic (from 2017) and in India. In this paper, we present the most interesting results of the SEVAN network operation during the last decade. We present this review on the occasion of the 10th anniversary of the International Heliophysical Year in 2007.

Strong variations of gamma-ray and atmospheric electric field during various meteorological conditions by observations in Yakutsk and Tiksi

The results of a study strong increase in gamma-ray background in the surface layer of the atmosphere during precipitation and near thunderstorms in Yakutsk (based on the Cosmic Ray Spectrometer of the Institute of Cosmic Rays of the Siberian Branch of the Russian Academy of Sciences) and Tiksi (Polar Geospace Observatory of the IKFIA SB RAS) are present in this paper. Scintillation detectors based on NaI (Tl) crystals with a size of 63mm x 63mm are used to register gammaray . The range of measured energies is 20-1900 keV. Detectors are closed from the sides and from below with lead (5 cm) and placed in thermoboxes having a glass window. Both of the detectors are located on the roof of buildings in Yakutsk and Tiksi. Also, synchronous registration of variations of the atmospheric electric field, (electrostatic fluxmeters Boltek EFM-100) and main meteorological parameters of the atmosphere (ultrasonic weather station AMK-04). An explicit relationship was found between the increase in the background gamma-ray and heavy rainfall. The energy spectra of the gamma background are obtained under “good” weather conditions and during heavy precipitation and near thunderstorms. The carried out researches allow to consider that the increase of the gamma background is connected, first of all, with the emission of radon and its daughter products from the ground and, to a lesser extent, with bremsstrahlung of charged particles in strong electric fields of a thunderstorm atmosphere.

Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches

The spectrum and spatiotemporal evolution of the fluorescence of an atmospheric discharge developing in the regime of relativistic runaway electron avalanche (RREA) generation have been calculated without involving the relativistic feedback. The discharges generating narrow bipolar pulses, along with the discharges responsible for terrestrial gamma-ray flashes, are shown to be relatively dark. Nevertheless, the fluorescence excited by a discharge involving RREAs can be recorded with cameras used to record high-altitude optical phenomena. A possible connection between a certain class of optical phenomena observed at the tops of thunderclouds and RREA emission is pointed out.

A method of determining basic thunderstorm field parameters from variations of cosmic ray muons detected by a horizontal array

An array of scintillators tightly packed in the horizontal plane and designed for recording secondary particles produced by cosmic rays is capable of probing the angular dependence of intensity disturbances caused by electric fields of a thunderstorm atmosphere. The basic parameters of thunderstorm activity are estimated using a specific example of variation in intensity in different ranges of energy release in the detectors. These parameters include the characteristic radius of the active region (5 km), its total charge (30 C), the accumulated electric field energy (6 GJ), and the potential difference in the stratosphere above the active thunderstorm region (375 MV).

Mount Aragats as a stable electron accelerator for atmospheric high-energy physics research

Observation of the numerous thunderstorm ground enhancements (TGEs), i.e., enhanced fluxes of electrons, gamma rays, and neutrons detected by particle detectors located on the Earth's surface and related to the strong thunderstorms above it, helped to establish a new scientific topic---high-energy physics in the atmosphere. Relativistic runaway electron avalanches (RREAs) are believed to be a central engine initiating high-energy processes in thunderstorm atmospheres. RREAs observed on Mount Aragats in Armenia during the strongest thunderstorms and simultaneous measurements of TGE electron and gamma-ray energy spectra proved that RREAs are a robust and realistic mechanism for electron acceleration. TGE research facilitates investigations of the long-standing lightning initiation problem. For the last 5 years we were experimenting with the ``beams'' of ``electron accelerators'' operating in the thunderclouds above the Aragats research station. Thunderstorms are very frequent above Aragats, peaking in May--June, and almost all of them are accompanied with enhanced particle fluxes. The station is located on a plateau at an altitude 3200 asl near a large lake. Numerous particle detectors and field meters are located in three experimental halls as well as outdoors; the facilities are operated all year round. All relevant information is being gathered, including data on particle fluxes, fields, lightning occurrences, and meteorological conditions. By the example of the huge thunderstorm that took place at Mount Aragats on August 28, 2015, we show that simultaneous detection of all the relevant data allowed us to reveal the temporal pattern of the storm development and to investigate the atmospheric discharges and particle fluxes.

Atmospheric discharges and particle fluxes

AbstractFluxes of the electrons, gamma rays, and neutrons observed by particle detectors located on the Earth's surface during thunderstorms originate so‐called Thunderstorm Ground Enhancements (TGEs). The relativistic runaway electron avalanches giving rise to TGEs originate in the thundercloud's lower dipole between the main negatively charged region in the middle of the thundercloud and transient lower positively charged region. Acceleration of electrons in the upper dipole between main negative and main positive charge regions leads to initiation of the terrestrial gamma flashes (TGFs) intensive researched during the last two decades by orbiting gamma ray observatories. TGFs are exceptionally intense, submillisecond bursts of electromagnetic radiation directed to the open space from the thunderstorm atmosphere. Unlike visible lightning, TGF beams do not create a hot plasma channel and optical flash; hence, in the literature they got name “dark lightning.” We investigate the TGEs development in 1 min and 1 s time series of particle detector count rates. Synchronized time series of the near‐surface electric field and lightning occurrences allows interconnecting two atmospheric phenomena. Registration of the Extensive Air Showers allows approaching problems of relation of the lightning occurrences and particle fluxes.

Comprehensive study of energetic particle processes in thunderclouds

In the course of an experiment studying variations of cosmic rays during thunderstorms at the Baksan Neutrino Observatory evidence has been obtained in favor of existence of a new type of large-scale electric discharge in thunderstorm atmosphere: a slow runaway electron breakdown in the near-threshold regime. Continuous glow of the stratosphere region above thunderclouds is discovered, correlating with anomalous disturbances in intensity of secondary cosmic rays detected on the ground.

Erratum to: “Fundamental processes capable of accounting for the neutron flux enhancements in a thunderstorm atmosphere”

Erratum to: “Fundamental processes capable of accounting for the neutron flux enhancements in a thunderstorm atmosphere”

On the origin of the particle fluxes from the thunderclouds: Energy spectra analysis

Simultaneous measurements of the gamma ray differential energy spectra, electric field disturbances, and meteorological conditions provided by experimental facilities located at Mt. Aragats in Armenia allows to establish the model of particle acceleration and propagation in thunderstorm atmosphere. We present comparisons of measured and modeled thunderstorm ground enhancements (TGEs). The origin of the majority of TGEs is the MOS process —the modification of energy spectra of cosmic ray electrons in the atmospheric electric fields. The gamma ray differential energy spectra are well described by the power law function with indexes in the range for the electric field strengths 0.8−1.5 kV/cm at altitudes of 3400−5000 m a.s.l. The good agreement of the characteristics of experimental and simulated TGEs gives hope to estimate the intracloud electric field by the observed parameters of TGE gamma ray energy spectra.

Erratum to: “On Amplifications of Photonuclear Neutron Flux in Thunderstorm Atmosphere and Possibility of Detecting Them”

The reliability of communications reporting observations of neutron flux enhancements in thunderstorm atmosphere is analyzed. The analysis is motivated by the fact that the employed gas-discharge counters on the basis of reactions 3He(n, p)3H and 10B(n; 4He, γ)7Li detect not only neutrons but any penetrating radiations. Photonuclear reactions are capable of accounting for the possible amplifications of neutron flux in thunder-storm atmosphere since in correlation with thunderstorms γ-ray flashes were repeatedly observed with spectra extending high above the threshold of photonuclear reactions in air. By numerical simulations, it was demonstrated that γ-ray pulses detected in thunderstorm atmosphere are capable of generating photonuclear neutrons in numbers sufficient to be detected even at sea level.

Electrode Layer in the Electric Field of Deep Convective Cloudiness

UDC 551.51; 551.594.2 We study variations in the light-ion concentration and space charge density in the atmospheric surface layer during the passage of deep convective clouds. Analysis of the experimental data for 2006–2012 shows matched variations in the positive and negative ion conductivities and both an increase and a decrease (down to zero) in the light-ion concentration at that time. An approach in which the electric field is the external driving force is proposed to describe the properties of the nonstationary electrode layer of the surface atmosphere during thunderstorms. It is shown that the transport of aeroions in the thunderstorm atmosphere is realized by both turbulent flows of air and electric forces, the latter playing a major role. The dynamics of changes in the electrode layer parameters as a function of the field variations has been identified.

Fundamental processes capable of accounting for the neutron flux enhancements in a thunderstorm atmosphere

Elementary processes capable of producing neutrons in a thunderstorm atmosphere are analyzed. The efficiency of nuclear fusion 2H(2H, n)3He, photonuclear reactions (γ, Xn), electrodisintegration reactions A(e −,n) −1 , and reactions e −(p +, n)ν e opposite to the β-decay is evaluated. It is shown that an unrealistically strong electric field is required for the nuclear fusion to be responsible for the neutron production in the lightning channel. The generation of neutrons in a thunderstorm atmosphere is connected with photonuclear (γ, Xn) and, at a much lower degree, electrodisintegration reactions, the relativistic runaway electron avalanches being primary parent processes.

Numerical analysis of 2010 high‐mountain (Tien‐Shan) experiment on observations of thunderstorm‐related low‐energy neutron emissions

AbstractThe high‐mountain experiment in a thunderstorm atmosphere, in which “extraordinary high flux of low‐energy neutrons” was detected, is analyzed. Due to the lack of data on the radiation source, we do not analyze directly measured absolute count rates. Instead, we address the experimental configuration, namely, simultaneous measurements by shielded and unshielded helium counters, which allow a comparison of relative count rates and, thus, verifying the species of the detected radiation. Results of Monte Carlo simulations of neutron transport executed without aprioristic assumptions, using only data on the experimental configuration, have raised strong doubts as to whether the detected increases of the count rates can be attributed to neutrons. Results of simulations allowing for the neutron transport in atmosphere from distant (100–500 m) photoneutron source with spectrum in the range 0–20.1 MeV produced by relativistic runaway electron avalanche bremsstrahlung demonstrate that ratios R of the count rates of shielded and unshielded counters below 1 keV are manyfold higher than the ratios Rexp ≈ 0.34–1.06 of the measured count rates. In the total range 0–20.1 MeV, the R magnitudes vary from 0.14 to 0.84 depending on the distance to the neutron source. Results of simulations of γ rays transport executed without aprioristic assumptions demonstrate that, most likely, hard γ rays with energies ϵγ > 1 MeV were detected. We note that in thunderstorm environment, a selection is required of neutrons and γ rays, for which the time‐of‐flight technique is the most adequate.

Thunderstorm ground enhancements: Gamma ray differential energy spectra

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 NaI 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 ($\ensuremath{\gamma}\ensuremath{\sim}\ensuremath{-}2$); 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 NaI 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.

Erratum to: “On Amplifications of Photonuclear Neutron Flux in Thunderstorm Atmosphere and Possibility of Detecting Them”

Erratum to: “On Amplifications of Photonuclear Neutron Flux in Thunderstorm Atmosphere and Possibility of Detecting Them”