Periodicities in Solar Flare Occurrence: Analysis of Cycles 19–23

Abstract

Midrange periodicities in solar flare occurrence have been analyzed with new methods for cycles 19-23. During cycle 23, periodicities of 129 and 33.5 days were in operation. Five episodes of high activity occurred periodically with the 129 day period. The 33.5 day periodicity mainly operated for energetic flares. Results for cycles 19-21 are generally in agreement with previous analyses. For cycle 19, the 51 day periodicity is confirmed to be statistically significant. In the spectrum for cycle 20, two peaks are found at 84 and 129 days. The 129 day periodicity was in operation for eight cycles of 129 days. The 153 day periodicity, which operated during cycle 21, was more effective for modulating occurrence rates of energetic flares than for those of less energetic flares. No statistically significant periodicities are found from occurrence rates of energetic flares (!M1.0) of cycle 22. In the power spectra of major flare occurrence times for the time intervals analyzed by Ozguc and Atac and by Bai, the strongest peaks are found at 73, 76, and 51 days, in agreement with their results, but these periodicities are not statistically significant. It is interesting that the periods of 51, 129, and 153 days are very close to integral multiples of 25.5 days.

Consistent long-term variation in the hemispheric asymmetry of solar rotation

“…2). This recent N-S asymmetry with a higher rotation rate in the north agrees with the results found for ALs, as determined from solar X-ray flares (Zhang et al 2008(Zhang et al , 2011aBai 2003), and with the results found for the rotation of H α filaments (Brajša et al 1997) and lowbrightness regions (Brajša et al 2000), but differs from the rotation found from magnetic flux (Song et al 2011), Doppler velocities (Hathaway et al 1996), and daily radio flux (Heristchi & Mouradian 2009). These differences may be, as discussed above, due to different methods, different time intervals, or real differences in rotation of features anchored at different depths in the solar atmosphere.…”

“…Discrepancies for the same tracers (for various authors) may be due to the time intervals and lengths of data included. Increasing evidence (Balthasar et al 1986;Bai 2003;Brajša et al 2006Brajša et al , 2007Balthasar 2007;Heristchi & Mouradian 2009) suggests that the solar differential rotation changes from cycle to cycle and even within one cycle. Bouwer (1992) claimed that precise rotation periods between 27 and 28 days persist only for a short time, sometimes only for a few solar rotations.…”

The Dynamics of the Solar Magnetic Field: Polarity Reversals, Butterfly Diagram, and Quasi-Biennial Oscillations

“…The most prominently recognized periods are the quasi-biennial oscillations (QBOs) at timescales around 2 yr. This component of the cycle, although weaker than the main component, has been identified in many activity indices (Rao 1973;Valdés-Galicia et al 1996;Bazilevskaya et al 2000;Kudela et al 2002;Bai 2003;Knaack & Stenflo 2005;Vecchio & Carbone 2008, 2009). The QBO origin is still unknown even if it could be related to the dynamo action in the inner solar layers (Benevolenskaya 1998), being also detected in phenomena directly connected with the solar interior.…”

The magnetic field in the solar atmosphere

“…Associated active features, including flares (Bai 2003;Zhang et al 2011) and coronal streamers (Li 2011) as well as superARs (i.e., ARs associated to repeated flaring and mass ejections, cf., Tian et al 2002) were found to be distributed inhomogeneously in solar longitude. They seemingly relate to "active nests" or "active longitudes", which had originally been postulated based on similar trends seen in surface magnetic field observations.…”