Observational Evidence of the Kink Instability in Solar Filament Eruptions and Sigmoids

Two lines of observational evidence are used to infer that the MHD helical kink instability is associated with solar eruptions. The sense of twist and writhe are determined in images of 7 erupting filaments obtained at 10830 Å, 1600 Å, 195 Å and 171 Å. In every case the sense of twist is the same as the sense of writhe, as required for a kink. From images in the soft X-ray and EUV spectrum, measurements of the height/width ratio of 623 sigmoids show a mean value of 5.47, which is the ratio expected for kinked flux ropes.