Periodicities Near 160 Minutes in Flare Occurrence

Abstract

The 160.01-min periodicity was originally found from line-of-sight velocities of the photosphere, and Kotov and Tsap reported a detection of the same periodicity in flare occurrence times. Intrigued by this, I analyze occurrence times of flares of cycles 19-23 to investigate periodicities in the neighborhood of 160 min, cycle by cycle. The 160.01-min periodicity is not detected from any cycle. However, a 160.69 min periodicity is detected in the spectrum for cycle 19, and a 160.32-min periodicity is detected in the power spectrum for major flares of cycle 21. The 160.32-min periodicity did not influence the occurrence rate of flares with X-ray classes below M3.0. Among major flares, the amplitude of modulation increases with increasing X-ray class.