Signature and escape of highly fractionated plasma in an active region

TL;DR

This study investigates the plasma composition and magnetic field evolution in a typical solar active region to understand the origins of highly fractionated plasma and its relation to space weather phenomena.

Contribution

It introduces a novel composition analysis technique combined with magnetic modeling to identify highly fractionated plasma in an active region, suggesting a general process for plasma release.

Findings

Highly fractionated plasma is located near coronal loop footpoints.

Magnetic reconnection at the active region boundary releases this plasma.

The process is likely common in active regions.

Abstract

Accurate forecasting of space weather requires knowledge of the source regions where solar energetic particles (SEP) and eruptive events originate. Recent work has linked several major SEP events in 2014, January, to specific features in the host active region (AR 11944). In particular, plasma composition measurements in and around the footpoints of hot, coronal loops in the core of the active region were able to explain the values later measured in-situ by the Wind spacecraft. Due to important differences in elemental composition between SEPs and the solar wind, the magnitude of the Si/S elemental abundance ratio emerged as a key diagnostic of SEP seed population and solar wind source locations. We seek to understand if the results are typical of other active regions, even if they are not solar wind sources or SEP productive. In this paper, we use a novel composition analysis technique, together with an evolutionary magnetic field model, in a new approach to investigate a typical solar active region (AR 11150), and identify the locations of highly fractionated (high Si/S abundance ratio) plasma. Material confined near the footpoints of coronal loops, as in AR 11944, that in this case have expanded to the AR periphery, show the signature, and can be released from magnetic field opened by reconnection at the AR boundary. Since the fundamental characteristics of closed field loops being opened at the AR boundary is typical of active regions, this process is likely to be general.