A statistical analysis of the contemporary (1954-1975) solar flare particle events has been made for the parametersF (integrated, proton fluence in cm-2 in an event with kinetic energy above 10 MeV) andR0 (the characteristic rigidity). These data are compared with the long-term averaged values determined from stable- and radio-nuclide measurements of lunar samples. The analysis shows that the ancient solar flare proton spectrum was harder (higher R0 values) compared to that observed in contemporary flares. A similar analysis can not be made for the mean long-term averaged flux (¯J, cm-2 S-1), since the contemporary averages suffer from an uncertainty due to the statistics of a single event. However, the average flux estimates for time durations 〈T〉 exceeding 103 yr, are free from such uncertainties. The long-term averaged ¯J values obtained over different time scales (104 - 106 yr) suggest a possible periodic variation in solar flare activity, with enhanced flux level during the last 105 yr. The available data rule out the occurrence of giant flares, with proton fluence exceeding 1015 cm-2 during the last million years.
Volume 40 | Issue 5
Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.
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