SUMER spectral observations of post-flare supra-arcade inflows

Abstract

On 21 April 2002 a large eruptive flare on the west limb of the Sun developed a bright, very dynamic, post-flare arcade. In TRACE 195 A images, a series of dark, sunward moving flows were seen against the bright extreme ultraviolet (EUV) arcade. SUMER obtained a series of spectra of the dark EUV flows in the lines C ii, Fe xii, and Fe xxi at a fixed position above the limb. These spectra give spatially resolved line-of-sight velocities and emission measures for the arcade plasma over a temperature range 2×104 to 107 K. The flows are dark in all SUMER lines. The UV continuum longward (∼ 1350 A) and shortward (∼ 675 A) of the hydrogen Lyman limit is used to determine whether the dark 195 A inflows are due to regions of low plasma density (plasma voids) or cold absorbing material. There is some evidence of absorption near the front of one of the inflows; however, along most of the dark channels there is no change in continuum ratio and we therefore conclude, as originally suggested by McKenzie and Hudson (1999), that they are plasma voids.