Editing Solar flare (section)

== Frequency ==
The frequency of occurrence of solar flares varies with the 11-year [[solar cycle]]. It can typically range from several per day during [[solar maximum|solar maxima]] to less than one every week during [[solar minimum|solar minima]]. Additionally, more powerful flares are less frequent than weaker ones. For example, [[#Classification|X10-class]] (severe) flares occur on average about eight times per cycle, whereas M1-class (minor) flares occur on average about 2000 times per cycle.<ref name="SWPCscales">{{cite web |title=NOAA Space Weather Scales |url=https://www.swpc.noaa.gov/noaa-scales-explanation |publisher=NOAA/NWS Space Weather Prediction Center |access-date=20 November 2021}}</ref>

[[Erich Rieger]] discovered with coworkers in 1984, an approximately 154 day period in the occurrence of [[gamma-ray]] emitting solar flares at least since the [[solar cycle 19]].<ref>{{Cite journal|title=A 154-day periodicity in the occurrence of hard solar flares?|year=1984|last1=Rieger|first1=E.|last2=Share|first2=G. H.|last3=Forrest|first3=D. J.|last4=Kanbach|first4=G.|last5=Reppin|first5=C.|last6=Chupp|first6=E. L.|journal=Nature|volume=312|issue=5995|pages=623–625|doi=10.1038/312623a0 |bibcode=1984Natur.312..623R|s2cid=4348672}}</ref> The period has since been confirmed in most heliophysics data and the [[interplanetary magnetic field]] and is commonly known as the [[Erich Rieger#Rieger period|''Rieger period'']]. The period's [[resonance]] [[harmonics]] also have been reported from most data types in the [[heliosphere]].

The [[frequency distribution]]s of various flare phenomena can be characterized by [[power-law distribution]]s. For example, the peak fluxes of radio, extreme ultraviolet, and hard and soft X-ray emissions; total energies; and flare durations (see {{slink|#Duration}}) have been found to follow power-law distributions.<ref>{{cite journal |last1=Kurochka |first1=L. N. |title=Energy distribution of 15,000 solar flares |journal=Astronomicheskii Zhurnal |date=April 1987 |volume=64 |page=443 |bibcode=1987AZh....64..443K}}</ref><ref>{{cite journal |last1=Crosby |first1=Norma B. |last2=Aschwanden |first2=Markus J. |last3=Dennis |first3=Brian R. |title=Frequency distributions and correlations of solar X-ray flare parameters |journal=Solar Physics |date=February 1993 |volume=143 |issue=2 |pages=275–299 |doi=10.1007/BF00646488 |bibcode=1993SoPh..143..275C}}</ref><ref>{{cite journal |last1=Li |first1=Y. P. |last2=Gan |first2=W. Q. |last3=Feng |first3=L. |title=Statistical analyses on thermal aspects of solar flares |journal=The Astrophysical Journal |date=March 2012 |volume=747 |issue=2 |pages=133 |doi=10.1088/0004-637X/747/2/133 |bibcode=2012ApJ...747..133L}}</ref><ref>{{cite book |last1=Aschwanden |first1=Markus J. |title=Self-Organized Criticality in Astrophysics: The Statistics of Nonlinear Processes in the Universe |date=2011 |publisher=Springer |location=Berlin, Heidelberg |doi=10.1007/978-3-642-15001-2 |isbn=978-3-642-15001-2 |url=https://link.springer.com/book/10.1007/978-3-642-15001-2 |url-access=subscription}}</ref>{{rp|23–28}}