Evolution of Plasma Composition in an Eruptive Flux Rope

Abstract

Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs). However, identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer observations of sigmoidal active region (AR) 10977. We analyze the coronal plasma composition in the AR and its evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and a sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical AR coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. Hence, plasma composition observations of AR 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level.

What Determines Active Region Coronal Plasma Composition?

“…The filament channel is seen as the dark feature in the EUV emission (Figure 7 the filament channel has distinctly lower FIP bias values than the rest of the AR. It is likely that this is due to flux cancellation taking place in the lower atmosphere (Baker et al 2022). Postreconnection loops bring photospheric material up into the corona, and plasma mixing leads to an overall lower FIP bias value.…”

“…Traces of high FIP bias are observed along some of the AR loops, indicating plasma starting to mix along loops (Baker et al 2013). Flux cancellation along the AR main polarity inversion line (PIL), along with the associated flux rope formation, leads to lower FIP bias levels (Baker et al 2013(Baker et al , 2022. Lower FIP bias levels were also found in the part of an AR where two failed eruptions occurred (Baker et al 2015).…”

The Eruption of a Magnetic Flux Rope Observed by Solar Orbiter and Parker Solar Probe

“…In addition to the FSI observations of the plasma flows, the SPICE spectrometer took a series of synoptic rasters of the region containing the flux rope (as noted in Section 2, with the field of view shown in Figures 1(a) and (b)). Previous work has shown that plasma composition can be used to determine where in the solar atmosphere a magnetic flux rope has formed, with Baker et al (2022) finding photospheric plasma composition within a flux rope, which they interpreted as evidence for flux rope formation via magnetic flux cancellation in the photosphere. Here, we attempted to estimate the plasma composition in two distinct regions observed by SPICE.…”

The case for solar full-disk spectral diagnostics: Chromosphere to corona

“…Signatures of energy build up leading to flares have been identified in the Doppler-shift and non-thermal broadening changes of coronal spectral lines in Hinode/EIS spectral rasters (Harra et al, 2009;Imada et al, 2014). Baker et al (2022) describe composition changes in a sigmoid prior to eruption as a coronal mass ejection (CME). In IRIS spectra, observations of magnetic flux rope formation exhibit Doppler-shifts and an increase in the non-thermal velocities during the pre-flare phase (Cheng et al, 2015).…”