The magnetic helicity sign of filament chirality

A solar prominence has either dextral or sinistral chirality depending on its axial field direction. We determine the magnetic helicity sign of filaments using high-resolution observations performed by Transition Region And Coronal Explorer. At EUV wavelengths, filaments sometimes appear as mixtures of bright threads and dark threads. This characteristic has enabled us to discern overlying threads and underlying ones and to determine the sign of magnetic helicity based on the assumption that the helicity sign of two crossing thread segments is the same as that of the filament. Our results support the notion that dextral filaments have negative magnetic and that sinistral filaments have positive helicity.