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Fluence Ordering of Solar Energetic Proton Events Using Cosmogenic Radionuclide Data |
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| Authors: | G A Kovaltsov I G Usoskin E W Cliver W F Dietrich A J Tylka |
| Institution: | 1. Ioffe Physical-Technical Institute, St. Petersburg, Russia 2. Sodankyl? Geophysical Observatory (Oulu unit), University of Oulu, Oulu, Finland 3. Department of Physics, University of Oulu, Oulu, Finland 4. Space Vehicles Directorate, Air Force Research Laboratory, Kirtland AFB, Albuquerque, NM, 87117, USA 5. National Solar Observatory, Sunspot, NM, 88349, USA 6. Praxis, Inc., Alexandria, VA, 22303, USA 7. Code 672, NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA |
| Abstract: | While data on the cosmogenic isotopes 14C and 10Be made it possible to evaluate extreme solar proton events (SPEs) in the past, their relation to standard parameters quantifying the SPE strengths, viz. the integrated fluence of protons with energy above 30 MeV, F 30, is ambiguous and strongly depends on the assumed shape of the energy spectrum. Here we propose a new index, the integral fluence of an SPE above 200 MeV, F 200, which is related to the production of the cosmogenic isotopes 14C and 10Be in the Earth atmosphere, independently of the assumptions on the energy spectrum of the event. The F 200 fluence is reconstructed from past cosmogenic isotope data, which provides an assessment of the occurrence probability density function for extreme SPEs. In particular, we evaluate that extreme SPEs with F 200>1010 cm?2 occur no more frequently than once per 10?–?15 kyr. |
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