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When we examine the chirality or observed handedness of the chromospheric andcoronal structures involved in the long-term build-up to eruptive events, wefind that they evolve in very specific ways to form two and only two sets oflarge-scale chiral systems. Each system contains spatially separated componentswith both signs of chirality, the upper portion having negative (positive)chirality and the lower part possessing positive (negative) chirality. Thecomponents within a system are a filament channel (represented partially bysets of chromospheric fibrils), a filament (if present), a filament cavity,sometimes a sigmoid, and always an overlying arcade of coronal loops. When weview these components as parts of large-scale chiral systems, we more clearlysee that it is not the individual components of chiral systems that erupt butrather it is the approximate upper parts of an entire evolving chiral systemthat erupts. We illustrate the typical pattern of build-up to eruptive solarevents first without and then including the chirality in each stage of thebuild-up. We argue that a complete chiral system has one sign of handednessabove the filament spine and the opposite handedness in the barbs and filamentchannel below the filament spine. If the spine has handedness, the observationsfavor its having the handedness of the filament cavity and coronal loops above.As the separate components of a chiral system form, we show that the systemappears to maintain a balance of right-handed and left-handed features, thuspreserving an initial near-zero net helicity. Each individual chiral system mayproduce many successive eruptive events above a single filament channel.

The Build-up to Eruptive Solar Events Viewed as the Development of Chiral Systems