Long-duration gamma-ray emissions from 2007 and 2008 winter thunderstorms

Abstract

The Gamma-Ray Observation of Winter THunderclouds (GROWTH) experiment, consisting of two radiation-detection subsystems, has been operating since 2006 on the premises of Kashiwazaki-Kariwa nuclear power plant located at the coastal area of Japan Sea. By 2010 February, GROWTH detected 7 long-duration $\gamma$-rays emissions associated with winter thunderstorms. Of them, two events, obtained on 2007 December 13 and 2008 December 25, are reported.On both occasions, all inorganic scintillators (NaI, CsI, and BGO) of the two subsystems detected significant gamma-ray signals lasting for >1 minute. Neither of these two events were associated with any lightning. In both cases, the gamma-ray energy spectra extend to 10 MeV, suggesting that the detected gamma-rays are produced by relativistic electrons via bremsstrahlung. Assuming that the initial photon spectrum at the source is expressed by a power-law function,the observed photons can be interpreted as being radiated from a source located at a distance of 290-560 m for the 2007 event and 110-690 m for the 2008 one, both at 90% confidence level.Employing these photon spectra, the number of relativistic electrons is estimated as 10^9 - 10^{11}. The estimation generally agrees with those calculated based on the relativistic runaway electron avalanche model. A GROWTH photon spectrum, summed over 3 individual events including the present two events and another reported previously, has similar features including a cut-off energy, to an averaged spectrum of terrestrial gamma-ray flashes.

46 pages, 13 figures, accepted for publication in JGR-Atmosphere

References in corpus (3)

• Detection of high-energy gamma rays from winter thunderclouds
• Observation of an energetic radiation burst from mountain-top thunderclouds
• Gamma-Ray Localization of Terrestrial Gamma-Ray Flashes

Cited by in corpus (12)

• Observation of thundercloud-related gamma rays and neutrons in Tibet
• Downward Terrestrial Gamma-ray Flash observed in Winter Thunderstorm
• Gamma Ray Glow Observations at 20-km Altitude
• Termination of Electron Acceleration in Thundercloud by Intra/Inter-cloud Discharge
• Hardening and termination of long-duration gamma rays detected prior to lightning
• Angular distribution of Bremsstrahlung photons and of positrons for calculations of terrestrial gamma-ray flashes and positron beams
• Positron clouds within thunderstorms
• TETRA Observation of Gamma Rays at Ground Level Associated with Nearby Thunderstorms
• The prolonged gamma ray enhancement and the short radiation burst events observed in thunderstorms at Tien Shan
• The emission of energetic electrons from the complex streamer corona adjacent to leader stepping
• Dynamics of positrons during relativistic electron runaway
• Characteristics of temporal variability of long-duration bursts of high-energy radiation associated with thunderclouds on the Tibetan plateau