The occurrence of powerful flares stronger than X10 class in Solar Cycles

TL;DR

This study analyzes the occurrence patterns of the most powerful solar flares (>X10 class) over solar cycles using satellite data and sunspot numbers, revealing correlations that could help predict future extreme flares.

Contribution

It introduces a heuristic model linking sunspot activity and flare occurrence, proposing a method to forecast extreme solar flares in upcoming cycles.

Findings

ES-flares mostly occur in late cycle phases and low-latitude regions.

Occurrence of ES-flares correlates with mean sunspot number and its deviation.

Prediction suggests about 2 ES-flares in solar cycle 25 after 2027.

Abstract

Solar flares stronger than X10 (S-flares, >X10) are the highest class flares which significantly impact on the Sun's evolution and space weather. Based on observations of Geostationary Orbiting Environmental Satellites (GOES) at soft X-ray (SXR) wavelength and the daily sunspot numbers (DSNs) since 1975, we obtained some interesting and heuristic conclusions: (1) Both S-flares and the more powerful extremely strong flares (ES-flares, >X14.3) mostly occur in the late phases of solar cycles and low-latitude regions on the solar disk; (2) Similar to X-class flares, the occurrence of S-flares in each solar cycle is somewhat random, but the occurrence of ES-flares seems to be dominated by the mean DSN (Vm) and its root-mean-square deviation during the valley phase (Vd) before the cycle: the ES-flare number is strongly correlated with Vd, and the occurrence time of the first ES-flare is anti-correlated with Vd and Vm. These facts indicate that the higher the Vm and Vd, the stronger the solar cycle, the more the ES-flares and the earlier they occurred. We proposed that the Sun may have a low-latitude active zone (LAZ), and most ES-flares are generated from the interaction between LAZ and the newly emerging active regions. The correlations and the linear regression functions may provide an useful method to predict the occurrence of ES-flares in an upcoming solar cycle, which derives that solar cycle 25 will have about 2 ES-flares after the spring of 2027.