Sabrina L. Savage, David E. McKenzie, Katharine K. Reeves
Following the eruption of a filament from a flaring active region,
sunward-flowing voids are often seen above developing post-eruption arcades.
First discovered using the soft X-ray telescope aboard Yohkoh, these
supra-arcade downflows (SADs) are now an expected observation of high-cadence
extreme ultra-violet (EUV) and soft X-ray coronal imagers and spectrographs
(e.g, TRACE, SOHO/SUMER, Hinode/XRT, SDO/AIA) as well as white-light
coronagraphs (SOHO/LASCO). Observations made prior to the operation of AIA
suggest that SADs are the cross-sections of flux tubes retracting from a
reconnection site high in the corona. The full disk field of view of AIA
ensures that a high percentage of flares are observed, and the high temperature
imaging afforded by AIA's 131 and 94 A channels coupled with the fast temporal
cadence allows for unprecedented scrutiny of the voids. For a flare occurring
on 2011 October 22, we provide evidence showing that SADs, instead of being
flux tube cross-sections, are actually wakes created by the retraction of thin
loops. We discuss the implications of this new interpretation of SADs on
previous parameter estimations and reconnection theory.
View original:
http://arxiv.org/abs/1112.3088
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