Oak Ridge National Laboratory

Physics Division

Physics Division Seminars

Physics Division Seminars bring us speakers on a variety of physics related subjects. Usually these are held in the Building 6008 large Conference Room, at 3:00 pm on the chosen day, but times and locations may vary. For more information, contact our seminar chairman,

Alfredo Galindo-Uribarri
Tel (Office): (865) 574-6124  (FAX): (865) 574-1268


Fri., July 15, 2011, at 3:00 p.m. (refreshments at 2:40 p.m.)

Thunderstorm ground enhancements (TGEs) evidence of the huge natural accelerators in the thunderclouds

Ashot Chilingarian, Director of Alikhanyan National Laboratory, Yerevan, Armenia
Building 6008 Conference Room

Strong electrical fields inside thunderclouds give rise to fluxes of high energy electrons and, consequently, gamma rays and neutrons. Gamma rays and electrons are currently detected by the facilities of low orbiting satellites and by networks of surface particle detectors. During intensive particle fluxes, coinciding with thunderstorms, series of particle bursts were detected by the particle detectors of Aragats Space Environmental Center (ASEC) on altitude of 3200 m. We classify the thunderstorm ground enhancements (TGEs) in 2 categories, one lasting microseconds, the other lasting up to tens of minutes. Both types of events can occur at the same time, coinciding with large negative electric field between cloud and ground and negative intracloud lightning occurrence. Statistical analysis of the short TGE bursts sample suggests the duration is less than 50 Ás and spatial extension is larger than 1000 m2. Huge enhancements of the particle fluxes (up to 800%) and short extended burst of particle showers point on relativistic runaway electron avalanches (RREA) process in the thunderclouds. The smaller peaks in the secondary cosmic ray fluxes (1-20% enhancements) can be explained without evoking particle multiplication in the avalanche process. We discuss the origin of TGEs and its connection to the terrestrial gamma flashes (TGF), detected by orbiting gamma-ray observatories. Simultaneously detected energy spectra of electrons and gamma rays recovered from largest TGE events detected at Aragats will be presented and discussed as well. Energy spectra are based on large statistics and prolonged up to 100 MeV. Detection of neutrons during TGE events also will be presented and discussed.

Local contact: J. B. Roberto, robertojb@ornl.gov 865-574-4750