Volume 592, August 2016
|Number of page(s)||13|
|Published online||15 August 2016|
Effects of flare definitions on the statistics of derived flare distributions
1 Solar-Terrestrial Center of Excellence, SIDC, Royal Observatory of Belgium, 1180 Brussels, Belgium
2 NASA Goddard Space Flight Center, Greenbelt, Maryland MD 20771, USA
3 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
4 NOAA National Centers for Environmental Information, Boulder, Colorado, USA
5 School of Computer Science and Statistics, Trinity College Dublin, O’Reilly Institute, Dublin 2, Ireland
Received: 14 January 2016
Accepted: 10 May 2016
The statistical examination of solar flares is crucial to revealing their global characteristics and behaviour. Such examinations can tackle large-scale science questions or give context to detailed single-event studies. However, they are often performed using standard but basic flare detection algorithms relying on arbitrary thresholds. This arbitrariness may lead to important scientific conclusions being drawn from results caused by subjective choices in algorithms rather than the true nature of the Sun. In this paper, we explore the effect of the arbitrary thresholds used in the Geostationary Operational Environmental Satellite (GOES) event list and Large Yield RAdiometer (LYRA) Flare Finder algorithms. We find that there is a small but significant relationship between the power law exponent of the GOES flare peak flux frequency distribution and the flare start thresholds of the algorithms. We also find that the power law exponents of these distributions are not stable, but appear to steepen with increasing peak flux. This implies that the observed flare size distribution may not be a power law at all. We show that depending on the true value of the exponent of the flare size distribution, this deviation from a power law may be due to flares missed by the flare detection algorithms. However, it is not possible determine the true exponent from GOES/XRS observations. Additionally we find that the PROBA2/LYRA flare size distributions are artificially steep and clearly non-power law. We show that this is consistent with an insufficient degradation correction. This means that PROBA2/LYRA should not be used for flare statistics or energetics unless degradation is adequately accounted for. However, it can be used to study variations over shorter timescales and for space weather monitoring.
Key words: methods: statistical / methods: data analysis / Sun: flares / Sun: X-rays, gamma rays / Sun: corona
© ESO, 2016
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