Reconnection microjets in the pre-eruption phase of a prominence/coronal rain complex

Abstract

Coronal rain is known to be one of the highest resolution tracers of the coronal magnetic field. In this work the dynamics of a prominence/coronal rain complex are analysed based on imaging and spectroscopic observations with IRIS. Prior to eruption, the loop-like magnetic field arcade hosting the rain is observed to slowly expand in height. This movement is accompanied by several small (~1 arsec) and short (<20 sec) bursts of plasma perpendicular to the field, captured in the Si IV and Mg II lines. The line profiles are broad and asymmetric with long tails above ~100 km/s. These microjets are accompanied with strong intensity enhancements along the loop in most of the AIA channels, indicating significant energy release. We interpret these microjets as reconnection outflows, produced by component reconnection as the magnetic structure expands transversely. The originally cold conditions of the rain allows in this case a unique high resolution glance at the reconnection dynamics in low beta plasmas