Observations of Reconnecting Flare Loops with the Atmospheric Imaging Assembly (AIA)

TL;DR

This paper presents new AIA observations of supra-arcade downflows in solar flares, providing evidence for magnetic reconnection and revealing their dynamics at larger heights, challenging simple 2D models.

Contribution

It offers novel measurements of downflows at greater heights and analyzes their properties, advancing understanding of magnetic reconnection in solar flares.

Findings

Downflows originate at larger heights than previously observed.

Initial velocities (~144 km/s) are below expected Alfvén speeds.

No brightening of downflows over time, contradicting chromospheric evaporation models.

Abstract

Perhaps the most compelling evidence for the role of magnetic reconnection in solar flares comes from the supra-arcade downflows that have been observed above many post-flare loop arcades. These downflows are thought to be related to highly non-potential field lines that have reconnected and are propagating away from the current sheet. We present new observations of supra-arcade downflows taken with the Atmospheric Imagining Assembly (AIA) on the \textit{Solar Dynamics Observatory} (\textit{SDO}). The morphology and dynamics of the downflows observed with AIA provide new evidence for the role of magnetic reconnection in solar flares. With these new observations we are able to measure downflows originating at much larger heights than in previous studies. We find, however, that the initial velocities measured here ($\sim$144\,km s$^{-1}$) are well below the Alfv{\'e}n speed expected in the lower corona, and consistent with previous results. We also find no evidence that the downflows brighten with time, as would be expected from chromospheric evaporation. These observations suggest that simple two-dimensional models cannot explain the detailed observations of solar flares.