Self-organization in the Corona and Flare Precursors

Abstract

Exploding loop systems producing X-ray flares often, but not always, bifurcate into a long-living, well-organized system of multithreaded loop arcades resembling solenoidal slinkies. The subject of this chapter is to look into the physical conditions that cause or prevent this process. We shall see that the X-class flares that bifurcate into long-living slinky arcades have different signatures than those which do not produce such structures. The most striking difference is that, in all cases of slinky formation, a high-energy proton (HEP) flux becomes significantly enhanced 10–40 h before the flare occurs. No such effect was found prior to the “non-slinky” flares. This fact is found to be associated with the difference between energy production by a given active region and the amount of energy required to bring the entire system into the form of self-organized loop arcades . One of the important features is that post-flare coronal slinky formation is preceded by scale-invariant structure formation in the underlying chromosphere/transition region. The observed regularities may serve as long-term precursors of strong flares and may help to study predictability of system behavior, and in particular, flare occurrence. We shall also discuss some aspects of recurrence of coronal microflares and flares which have signatures consistent with spatial and temporal plasma echoes .