Solar Disappearing Filament Inside a Coronal Hole

Abstract

Based on Yohkoh/SXT, SOHO/EIT images and movies, as well as on Hα, He I 10830 Å heliograms and other relevant data, we analyze an event of 1999 December 28, which is interesting in at least two aspects. (1) A major horseshoe-shaped Hα filament appeared to be located within a large transequatorial coronal hole (CH) in the eastern hemisphere. (2) This filament subsequently disappeared, with its eruption combined with a number of dynamic phenomena, including large-scale ones. The probable location of the filament inside the CH was confirmed in detail by calculations of the open field regions and, for the first time, the quasi-separatrix layers in the global solar magnetic field. The filament eruption was accompanied by significant evolution of the soft X-ray and EUV-emitting structures inside the CH as well as by a coronal mass ejection. The analysis indicates that CHs need not have the simple and uniform structure normally assumed and can sometimes contain local areas with low-altitude closed magnetic fields. It demonstrates also that the erupting filament inside the CH was a part of a much more global, evolving magnetic structure associated with activity extending through at least the entire eastern half of the disk.