On Flare Predictability Based on Sunspot Group Evolution

Abstract

The forecast method introduced by Korsós et al. (2014) is generalised from the horizontal magnetic gradient (G M ), defined between two opposite polarity spots, to all spots within an appropriately defined region close to the magnetic neutral line of an active region. This novel approach is not limited to searching for the largest G M of two single spots as in previous methods. Instead, the preflare conditions of the evolution of spot groups is captured by the introduction of the weighted horizontal magnetic gradient, or W G M . This new proxy enables the potential of forecasting flares stronger than M5. The improved capability includes (i) the prediction of flare onset time and (ii) an assessment whether a flare is followed by another event within about 18 hours. The prediction of onset time is found to be more accurate here. A linear relationship is established between the duration of converging motion and the time elapsed from the moment of closest position to that of the flare onset of opposite polarity spot groups. The other promising relationship is between the maximum of the W G M prior to flaring and the value of W G M at the moment of the initial flare onset in the case of multipleflaring. We found that when the W G M decreases by about 54%, then there is no second flare. If, however, when the W G M decreases less than 42%, then there will be likely a follow-up flare stronger than M5. This new capability may be useful for an automated flare prediction tool.

Applying the Weighted Horizontal Magnetic Gradient Method to a Simulated Flaring Active Region

“…We investigate the preflare behavior of the simulated 3D δ-type sunspot with the tool put forward by Korsós et al (2015). Namely, they introduced the weighted horizontal magnetic gradient proxy (denoted as WG M ) between two opposite magnetic polarity umbrae in a δ-spot and demonstrated that the WG M could be successfully applied to identifying preflare patterns above the M5 energetic flare class.…”

ON THE STATE OF A SOLAR ACTIVE REGION BEFORE FLARES AND CMEs

“…An accurate variation of probability should include simultaneous parallel methods (and parameters) for which the two proxies suggested above may be helpful, among (or complementary to) other methods. In the future, we would like to automate the identification of the weighted horizontal magnetic gradient applied by Korsós et al (2015a). Therefore, here we have tried to find more reliable forecast parameters that could narrow down the identification of larger intensity flaring ARs with an associated fast CME.…”

“…This behavior is promising for flare-forecast perspectives because, when G M starts to decrease after a pronouced maximum, this pattern may be considered to be a warning signal of eruption(s). Later, the method of Paper I was further developed and the weighted horizontal magnetic gradient, or WG M (Korsós et al 2015a), was introduced. This new proxy enables the potential to forecast flares stronger than M5.…”

“…The improved capability includes (i) the prediction of flare onset time and (ii) an assessment of whether a flare will be followed by another event within about 18 hr. In the future, we would like to automate the method outlined in Korsós et al (2015a). Driven by this desire, therefore, in this paper we seek to find even more reliable precursors for identifying with high probability ARs with the potential for flare/CME activities.…”

“…It is our aim that only ARs passing a certain set of evaluation criteria would be further investigated, analyzed, and followed by such automated methods (e.g., WG M or other) in the not too distant future. In what follows, we discuss only flaring ARs, because flaring and non-flaring ARs were tested separately on a large sample by Korsós et al (2015a). We found differences in the behavior of the separation, between the area-weighted centers of opposite polarities, of flaring and non-flaring ARs.…”