Field Line Shrinkage in Flares Observed by the X‐Ray Telescope on Hinode

Abstract

The X-Ray Telescope on Hinode has observed individual loops of plasma moving downward in a manner that is consistent with field line shrinkage in the aftermath of reconnection at higher altitudes. An on-disk B3.8 flare observed on 2007 May 2 has loops that clearly change in shape from cusp-shaped to more rounded. In addition, bright loops are observed that decrease in altitude with a speed of approximately 5 km s-1, and fainter, higher loop structures shrink with a velocity of 48 km s-1. A C2.1 flare observed on 2006 December 17 also has loops that change shape. Many bright features are seen to be moving downward in this event, and we estimate their speed to be around 2-4 km s-1. We measure the shrinkage in both of these events, and find that it is 17%-27%, which is consistent with theoretical predictions.