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Science 18 February 2005:
Vol. 307. no. 5712, pp. 1085 - 1088
DOI: 10.1126/science.1107466
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Reports

Terrestrial Gamma-Ray Flashes Observed up to 20 MeV

David M. Smith,1* Liliana I. Lopez,2 R. P. Lin,3 Christopher P. Barrington-Leigh4

Terrestrial gamma-ray flashes (TGFs) from Earth's upper atmosphere have been detected with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite. The gamma-ray spectra typically extend up to 10 to 20 megaelectron volts (MeV); a simple bremsstrahlung model suggests that most of the electrons that produce the gamma rays have energies on the order of 20 to 40 MeV. RHESSI detects 10 to 20 TGFs per month, corresponding to ~50 per day globally, perhaps many more if they are beamed. Both the frequency of occurrence and maximum photon energy are more than an order of magnitude higher than previously known for these events.

1 Physics Department and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA.
2 Astronomy Department and Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94720, USA.
3 Physics Department and Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94720, USA.
4 University of British Columbia, 2329 West Mall Vancouver, BC V6T 1Z4 Canada.

* To whom correspondence should be addressed. E-mail: dsmith{at}scipp.ucsc.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)