title: Detection of high-energy gamma rays from winter thunderclouds.
abstract: A report is made on a comprehensive observation of a burstlike gamma-ray emission from thunderclouds on the Sea of Japan, during strong thunderstorms on 6 January 2007. The detected emission, lasting for approximately 40 sec, preceded cloud-to-ground lightning discharges. The burst spectrum, extending to 10 MeV, can be interpreted as consisting of bremsstrahlung photons originating from relativistic electrons. This ground-based observation provides the first clear evidence that strong electric fields in thunderclouds can continuously accelerate electrons beyond 10 MeV prior to lightning discharges.
authors.affiliation: Cosmic Radiation Laboratory, Riken, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Tsuchiya
authors.forename: T
authors.initials: T
authors.lastname: Enoto
authors.forename: S
authors.initials: S
authors.lastname: Yamada
authors.forename: T
authors.initials: T
authors.lastname: Yuasa
authors.forename: M
authors.initials: M
authors.lastname: Kawaharada
authors.forename: T
authors.initials: T
authors.lastname: Kitaguchi
authors.forename: M
authors.initials: M
authors.lastname: Kokubun
authors.forename: H
authors.initials: H
authors.lastname: Kato
authors.forename: M
authors.initials: M
authors.lastname: Okano
authors.forename: S
authors.initials: S
authors.lastname: Nakamura
authors.forename: K
authors.initials: K
authors.lastname: Makishima