Solar Flare Build-Up and Release

Abstract

Flares and coronal mass ejections should follow a pattern of build-up and release, with the build-up phase understood as the gradual addition of stress to the coronal magnetic field. Recently Hudson (Mon. Not. Roy. Astron. Soc.491, 4435, 2020) presented observational evidence for this pattern in two isolated active regions from 1997 and 2006, finding a correlation between the waiting time after the event, and the event magnitude. In this article we systematically search for related evidence in the largest 14 active regions of Solar Cycle 24, chosen as those with peak sunspot area exceeding 1000 millionths of the solar hemisphere (MSH). The smallest of these regions, NOAA 12673, produced the exceptional flares SOL2017-09-06 and SOL2017-09-10. None of these regions showed significant correlations of waiting times and flare magnitudes, although two hinted at such an interval-size relationship. Correlations thus appear to be non-existent or intermittent, depending on presently unknown conditions.

A Statistical Search for a Uniform Trigger Threshold in Solar Flares from Individual Active Regions

“…Crosscorrelations between the size of a flare and the subsequent (preceding) waiting time, henceforth termed forward (backward) cross-correlations, are a key differentiator between the stress-relax and avalanche descriptions: the latter predicts no size-waiting-time cross-correlations (Jensen 1998). Forward and backward correlations are broadly absent from solar flares data sets (Biesecker 1994;Crosby et al 1998;Hudson et al 1998;Wheatland 2000a;Hudson 2020), with the exception of strong forward cross-correlations found in two active regions (Hudson 2019).…”

Deciphering Solar Magnetic Activity. The Solar Cycle Clock

“…Such clustering timescales are consistent with the period of a Rossby wave propagating in the solar tachocline . Hudson (2020) has also tried to explain clustering, but in terms of a "waiting time" relaxation oscillator, but he also notably remarked that there is a "last best flare" for each solar cycle (Hudson, 2018), as has Chapman et al (2020). Similarly, the first X-flare (or flare cluster) of a cycle also seems to happen within a rotation or two of the terminator.…”

“…We also use longerterm synoptic ground-based solar observations, including the Penticton 10.7cm radio flux 4 (Tapping, 2013); and the NGDC composite Coronal Green Line (Fe xiv) data 5 (Rybansky et al, 1994). Sunspot number data is from the Solar Information Data Center (SIDC; SILSO World Data Center, 1960-2020Vanlommel et al, 2005), and sunspot area from the combined Royal Greenwich Observatory/ United States Air Force record, originally compiled and maintained by NASA's Marshall Space Flight Center 6 (Hathaway, 2015).…”

Editorial: Towards Future Research on Space Weather Drivers

“…The TC contains three articles that directly address this topic. On one hand, one of them includes a fundamental investigation of the physical processes associated with solar flare precursors (Hudson, 2020), and, on the other, the remaining two are applied investigations toward forecasting applications (Morales and Santos, 2020;Cinto et al, 2020). Following the previous studies, Hudson (2020) systematically searched for the evidence of a build-up and release pattern of flare-CME behavior in the 14 largest active regions of Solar Cycle 24.…”

“…On one hand, one of them includes a fundamental investigation of the physical processes associated with solar flare precursors (Hudson, 2020), and, on the other, the remaining two are applied investigations toward forecasting applications (Morales and Santos, 2020;Cinto et al, 2020). Following the previous studies, Hudson (2020) systematically searched for the evidence of a build-up and release pattern of flare-CME behavior in the 14 largest active regions of Solar Cycle 24. The research by Morales and Santos (2020) revisited the Lu and Hamilton avalanche model for solar flares in order to explore its predicting capabilities for large events.…”