Coronal Sigmoids and Chromospheric Filaments - A relation?
Abstract
Sigmoids are forward (S-shaped) or inverse (Z-shaped) features on the Sun that are seen at coronal heights in X-ray or high temperature extreme ultraviolet (EUV) wavelengths. The sharpest and brightest of them are highly eruptive. They usually deform or disappear via coronal mass ejections. This makes it important to understand X-ray sigmoids because of their relevance for space-weather forecasting purposes. Chromospheric filaments are generally observed as absorption features in H$\alpha$ wavelengths. In this work, we observe chromospheric filaments lying under the sigmoids in order to correlate the chiralities of the two features. We expect that if the formation mechanisms of filaments and sigmoids are similar then they should have same chirality. We have conducted a joint survey of the sigmoids and the underlying filaments between 2007 and 2017. We use Hinode soft and hard X-ray data for sigmoid images and GONG H$\alpha$ data for the filaments. We find a total of 84 sigmoids with filaments within the said time period. Among these we have 41 forward and 43 inverse sigmoids. In the 41 forward sigmoids, 8 (20%) filaments are dextral, 21 (50%) are sinistral and 12 (30%) ambiguous. In the inverse sigmoids, 16 filaments (37%) are dextral, 13 (30%) sinistral and 14 (33%) ambiguous. It is evident from this analysis that there is no clear correspondence between filament chirality and the sigmoid handedness. This result warrants further investigation. We therefore perform calculations of magnetic helicity in the photospheric regions that encloses the footprints of sigmoids and filaments to primarily obtain the sign of their helicities. For many of the cases mentioned above, we use SHARP (Space-weather HMI Active Region Patch) vector magnetograms to serve as the photospheric boundary condition to which we apply the linear force-free magnetic helicity and energy formulations of Georgoulis \& LaBonte (2007). We will report on the findings of this study during the 43rd COSPAR General Assembly. References Georgoulis, M. K. \& LaBonte, B. J., ApJ, 2007, 671, 1034
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1765V