Soft X-ray coronal structure surrounding high-latitude dark filaments observed by Yohkoh

The faint coronal structure existing prior to high-latitude X-ray arcade fo rmation observed by the Yohkoh Soft X-ray Telescope has turned out to be "o verlapped dual arcades" whose inside legs cross with one another, rather th an being a simple bipolar arcade whose top part is sagging due to loading o f the dark filament material, as considered in previous models of dark fila ment suspension. The photospheric magnetic field under the crossed legs is found to be a belt of mixed polarity, extending tens of thousand kilometers , rather than a clean border of the two extended unipolar regions. The magn etic field distribution, as well as the coronal structure above it, are ver y different from the previously assumed situation for dark filaments based on the assumption of a bipolar photospheric magnetic held distribution. The coronal structure found in the region, the "overlapped dual arcades" struc ture, is most likely to be the "separatrix surfaces" in the quadruple photo spheric magnetic source model for the magnetic configuration surrounding a dark-filament, as proposed by one of the present authors in his previous wo rk (Uchida 1980, AAA 28.073.129).