Observation of thundercloud-related gamma rays and neutrons in Tibet

Abstract

During the 2010 rainy season in Yangbajing (4300 m above sea level) in Tibet, China, a long-duration count enhancement associated with thunderclouds was detected by a solar-neutron telescope and neutron monitors installed at the Yangbajing Comic Ray Observatory. The event, lasting for $40 min , was observed on July 22, 2010. The solar-neutron telescope detected significant -ray signals with energies >40 MeV in the event. Such a prolonged high-energy event has never been observed in association with thunderclouds, clearly suggesting that electron acceleration lasts for 40 min in thunderclouds. In addition, Monte Carlo simulations showed that >10 MeV rays largely contribute to the neutron monitor signals, while >1 keV neutrons produced via a photonuclear reaction contribute relatively less to the signals. This result suggests that enhancements of neutron monitors during thunderstorms are not necessarily clear evidence for neutron production, as previously thought.

Relativistic electron avalanches as a thunderstorm discharge competing with lightning

“…Because gamma-ray glows persist for seconds to minutes 30,31 , most of the discharge current resulting from runaway electrons will come from the drifting ions and not the low-energy electrons or runaway electrons 16 . In the runaway electron avalanche region, energy spectra for each particle type for the best-fit RREA model.…”

“…There is an uncertainty in the glow discharge rate of about 30% due to uncertainties of the mass distribution of the plane (see above subsection). While we measured the glow for only 4 s, it is reasonable to assume the glow was active for much longer since groups on the ground measure glows for several minutes 31,43 . From the rest of our glow measurements, we know that glows are occurring near active storm cells at least 8% of the time.…”

Effect of near-earth thunderstorms electric field on the intensity of ground cosmic ray positrons/electrons in Tibet

“…The intensity enhancements of ground cosmic rays have been detected by high altitude experiments, such as the Carpet air shower array [10,11], EAS-TOP [12], ASEC [13][14][15][16][17] and ASγ [18]. Their results indicated that the increases were associated with the electric field and the RREA process could be responsible for huge TGEs.…”

Remarks on recent results on neutron production during thunderstorms

“…Recently, three papers were published [1][2][3] on measuring the sizable neutron fluxes that were registered during thunderstorms. All three measurements were done at high altitudes 1 with neutron monitors [4] and thermal neutron counters.…”

“…The Tien-Shan group reports large fluxes of thermal neutrons correlated with atmospheric discharges; the Aragats and Tibet groups do not relate the neutron flux to lightning occurrences, but rather to photonuclear reactions of the bremsstrahlung gamma rays born in the relativistic runaway electron avalanches (RREA) [5] (also referred to as runaway breakdown [6]) in the thunderstorm atmospheres. However, the Tibet group assumes that gamma rays directly initiate NM counts by photonuclear reactions with lead producer of NM [3]; the Aragats group accepts the photonuclear reaction of the RREA gamma rays with the atmosphere as a source of neutrons [1].…”