TEPA-2018 Proceedings published!
The Thunderstorms and Elementary Particle Acceleration (TEPA-2018) conference was devoted to the 10 Years of Thunderstorm Ground Enhancement (TGE) observations on Mt. Aragats. In the TEPA-2018 Proceedings, 17 reports are collected. Some reports have already been published, while others have been submitted for publication. All are compiled under one cover to provide a comprehensive picture of advances in the high-energy atmospheric physics as reported at the TEPA-2018 conference. This is the 4th publication of TEPA proceedings, which includes results from the previous 7 conferences. TEPA conferences and the proceedings are helping to shape a new scientific direction - High-Energy Atmospheric Physics (HEAP). HEAP is a rather new scientific discipline aimed at classifying and explaining thunderstorm correlated fluxes of electrons and gamma rays. In the Near-Earth space these consist of Terrestrial Gamma Flashes – TGFs; in the troposphere - gamma glows; and on the earth’s surface, Thunderstorm Ground Enhancements - TGEs. All three types of experiments (in space, in the troposphere, and on the earth’s surface) are accompanied by observations of lightning flashes and atmosphere electrification. TGF observations are synchronized with worldwide lightning location networks and by optical observations of lightning flashes by orbiting high-frequency cameras. Gamma glow and TGEs are measured by detecting electric fields on the earth’s surface and high in the atmosphere.
The central engine initiating TGEs is believed to be the Relativistic Runaway Electron Avalanches (RREAs) which accelerate and multiply seed electrons from an ambient population of Cosmic Rays (CRs) in the large-scale strong atmospheric electric fields. These initiate minute-long bursts of radiation and electrons, and sometimes neutrons, with energies up to many tens of MeV. The complementary mechanism, electron energy Modification Of Spectra (MOS), leads to enhancement of gamma radiation from the atmosphere even in weak electric fields. These enhancements can last for a very long time, up to hours. The recent observations of numerous TGFs, TGEs, and gamma glows prove that RREA and MOS are robust and realistic mechanisms for explaining HEAP physics. Models using CERN GEANT4 code and CORSIKA code from Karlsruhe Institute of Technology, now both supplemented by the atmospheric electric field option, are in agreement with in situ measurements of electron and gamma ray energy spectra.
The 7-th edition of TEPA symposia held at Nor Amberd, Republic of Armenia, in September 2018, coincides with 10 years of TGE observations on Mt. Aragats. Nearly 500 TGEs detected at Aragats during the past decade can be widely used for the validation of models aimed at explaining high-energy phenomena in the atmosphere. The ground-based experiments have a huge advantage over the space and atmospheric based ones, because a “beam” of electrons is frequently located directly above the particle detectors, and usually at distances of few tens of meters. Thus, on Aragats, it was possible to measure the RREA avalanches initiated by a single CR electron, estimate the energy spectra of TGE electrons and gamma rays, and perform well synchronized measurements of lightning discharges and particle fluxes. This explained the phenomenon of the abrupt decline of the high-energy part of TGEs and provided clues to the dynamics of atmospheric electric fields.
The problem of thundercloud electrification is one of the most difficult ones in atmospheric physics. The structure of electric fields in the atmosphere still remains hidden from the detailed in situ measurements. A few balloon flights, although providing us with overall knowledge on possible structures and strengths of the atmospheric electric fields, cannot reveal the dynamics of the intracloud electric field. By simultaneously observing the origination and decline of TGEs with atmospheric discharges we can understand how the charge structure of the cloud is changing during a thunderstorm and how lightning itself originates.
Physicists and students from Russia, US, Italy, Japan, and Armenia discussed these and other problems of high-energy physics in the atmosphere through the 4-day long meeting. During a visit to the Mt. Aragats high-altitude research station, the operation of numerous particle detectors, lightning sensors, and field meters were demonstrated, the measurements of which were jointly analyzed to reveal the relationships between atmospheric discharges and particle fluxes.
TEPA proceedings appear also in Repository of the International Nuclear Information System (INIS).
Special thanks to our designer Narine Khachatryan for making the proceedings so attractive!