Supra-arcade downflows

Supra-arcade downflows (SADs) are sunward-traveling plasma voids that are sometimes observed in the Sun's outer atmosphere, or corona, during solar flares.

[1] SADs are byproducts of the magnetic reconnection process that drives solar flares, but their precise cause remains unknown.

SADs are typically observed using soft X-ray and Extreme Ultraviolet (EUV) telescopes that cover a wavelength range of roughly 10 to 1500 Angstroms (Å) and are sensitive to the high-temperature (100,000 to 10,000,000 K) coronal plasma through which the downflows move.

[1] Observations soon followed from the Transition Region and Coronal Explorer (TRACE, 1998–2010), an EUV imaging satellite, and the spectroscopic SUMER instrument on board the Solar and Heliospheric Observatory (SOHO, 1995–2016).

[3][4] More recently, studies on SADs have used data from the X-Ray Telescope (XRT) onboard Hinode (2006—present) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO, 2010—present).

[1][7] This interpretation was later revised to suggest that SADs are instead wakes behind much smaller retracting loops (SADLs),[8] rather than cross sections of the flux tubes themselves.

Solar flare observed by TRACE 195 Å on 2002 April 21. SADs can be seen at center frame–note the dark "tadpoles" descending toward the bright coronal loop arcade.
SADs observed by SDO AIA 131 Å on 2011 Oct 2.