A.L. Shepetov

Intensive X-ray emission bursts during thunderstorms

Abstract The intensive X-ray emission during thunderstorms was studied at a height of 3340 m above sea level. For the first time, short-time (1–5 min) bursts of X-ray emission were observed. The bursts are highly correlated over a wide space region (about 0.5 km). The main component of X-ray emission in bursts has energies between 50–80 keV. The observed bursts could be attributed to the bremsstrahlung determined by the runaway breakdown (RB) effect in the thunderclouds electric field. Ground-based observations of RB open a wide range of opportunities for the studies of fundamental processes in thunderstorms.

Effective growth of a number of cosmic ray electrons inside thundercloud

Abstract Significant enhancement of secondary cosmic ray electrons inside electrically charged clouds is established. The effect is observed in a quiet phase of thunderstorm—in the absence of lightning, rainfall and bursts of X-ray emission. The observations are fulfilled in Tien-Shan Mountains at the modernized thunderstorm–cosmic ray (TCR) installation [Phys. Lett. A 275 (2002) 90; J. Phys. G 28 (2) (2002) 251].

The influence of background radiation on the events registered in a neutron monitor at mountain heights

We have made an experimental check of an influence caused by external background of slow thermal neutrons on the temporal distribution of the signals from the standard NM64 supermonitor used as a detector of hadron component of extensive air showers with the energy above 1015 eV. Special attention in our study was paid to the possible connection of this background with the anomalously (up to a few milliseconds) delayed signals from the neutron monitor which were detected when the shower cores passed in its close vicinity. It has been found that in spite of the long, up to tens of milliseconds, presence of thermal neutrons nearby the shower axis, these external neutrons do not have any effect on the temporal behaviour of the neutrons diffusing inside the monitor as well as on the distribution of gamma-radiation accompanying the absorption of the latter.

Bursts of gamma-rays, electrons and low-energy neutrons during thunderstorms at the Tien-Shan

New data of the last measurement season held at the Tien-Shan complex for investigation gamma-radiation, accelerated electrons and low-energy neutrons during thunderstorms are presented. The flux of gamma-radiation in the energy range of 40 – 1200 keV shows a strict correlation with instantaneous intensity of atmospheric discharge. Its energy spectra measured for the first time with riches statistics and improved resolution typically have an absolute intensity about 50 – 100 quanta·cm−2·s−1, and demonstrate considerable evolution in the course of discharge. The signals from an avalanche of accelerated electrons have been directly observed inside thunderclouds. A lower energy estimation for these electrons is about 10 MeV. For the first time, during electric discharge moments in thunderstorms, there were found considerable intensity enhancements of the neutron intensity in the range of thermal energies: up to 100 – 200 standard deviations, or 3 – 8 times above the background, so the observed neutron flux reaches the values of (20 – 40) · 103 m−2 · min−1.

Measurements of the energy spectrum of lightning gamma emission on the Tien-Shan Cosmic Ray Station

The results of gamma emission observations obtained during thunderstorms at Tien-Shan Mountain Cosmic Ray Station are presented. The energy spectrum radiation of the stepped leader gamma radiation is measured. The experimental results are in an agreement with the runaway breakdown mechanism.

Observation of the intercloud discharge induced by an extensive air shower in a thunderstorm atmosphere

The observational evidence of RB-EAS discharge in a thunderstorm atmosphere is presented. After RB-EAS discharge we name a discharge of a special type developing due to the runaway breakdown (RB) mechanism while an extensive atmosphere shower (EAS) passes through a thundercloud electric field. The observations were fulfilled at the Tien-Shan Mountain Cosmic Ray Station. The widely spread system of scintillation detectors, the special EAS trigger array and the HF radio interferometer were used for measurements.