Transient Inverse-FIP Plasma Composition Evolution within a Solar Flare

Abstract

Understanding elemental abundance variations in the solar corona provides an insight into how matter and energy flow from the chromosphere into the heliosphere. Observed variations depend on the first ionization potential (FIP) of the main elements of the Sun's atmosphere. High-FIP elements (>10 eV) maintain photospheric abundances in the corona, whereas low-FIP elements have enhanced abundances. Conversely, inverse FIP (IFIP) refers to the enhancement of high-FIP or depletion of low-FIP elements. We use spatially resolved spectroscopic observations, specifically the Ar XIV/Ca XIV intensity ratio, from Hinode's Extreme-ultraviolet Imaging Spectrometer to investigate the distribution and evolution of plasma composition within two confined flares in a newly emerging, highly sheared active region. During the decay phase of the first flare, patches above the flare ribbons evolve from the FIP to the IFIP effect, while the flaring loop tops show a stronger FIP effect. The patch and loop compositions then evolve toward the pre-flare basal state. We propose an explanation of how flaring in strands of highly sheared emerging magnetic fields can lead to flare-modulated IFIP plasma composition over coalescing umbrae which are crossed by flare ribbons. Subsurface reconnection between the coalescing umbrae leads to the depletion of low-FIP elements as a result of an increased wave flux from below. This material is evaporated when the flare ribbons cross the umbrae. Our results are consistent with the ponderomotive fractionation model (Laming 2015) for the creation of IFIP-biased plasma.

Can Subphotospheric Magnetic Reconnection Change the Elemental Composition in the Solar Corona?

“…In this paper, magnetic field and continuum observations of the most unusual and complex magnetic field of AR 12673are combined with Hinode/EIS scans to investigate the presence of I-FIP effect plasma. We confirm the findings of Baker et al (2019) and provide evidence in support of the generation of I-FIP effect plasma by subphotospheric reconnection in coalescing sunspot umbrae with strong light bridges (LBs). The paper is organized as follows: Section 2 describes the magnetic field evolution, Section 3 details the Hinode/EIS observations, Section 4 provides our analysis and interpretation of the observations of anomalous plasma composition in the context of the ponderomotive force fractionation model, and in Section 5 we present our conclusions.…”

“…These waves are refracted/ reflected in the chromosphere, leading to a downward oriented ponderomotive force which depletes the low-FIP ions from the chromosphere. The general scenario is consistent with Baker et al (2019). In the specific light bridge scenario (c) proposed in Section 4.4, subphotospheric reconnection launches incompressible (shear) Alfvén waves along the magnetic field lines at the edges of the light bridge.…”

“…Though Ar XIV and Ca XIV have similar contribution functions, it is not immediately apparent what, if any, temperature effects flaring might have on the uncertainties of the I-FIP effect measurements, as large flares can have much higher densities (N) at high temperatures (T) (e.g., Watanabe et al 2010;Graham et al 2011;Simões et al 2015) compared to nonflaring active regions (Doschek et al 2007;Tripathi et al 2008). The Ar XIV/Ca XIV ratio can vary by a factor ∼4 in the log 10 T=6.6-6.9 range (with T in K, see e.g., Doschek & Warren 2017;Baker et al 2019).…”

“…Three Gaussians were fit to the Ar XIV 194.40 Å emission line to remove two unidentified lines in its blue wing. The Ca XIV 193.87 Å line was also fit with three Gaussians to separate the line from nearby Fe X 193.72 Å, Ni XVI 194.05 Å, and 194.10 Å lines (Brown et al 2008;Doschek et al 2015;Baker et al 2019).…”

“…Recently, Katsuda et al (2020) reported the I-FIP effect in four large X-class flares (X17.0, X5.4, X6.2 from AR 10808 and X9.0 from AR 10930) derived from Earth albedo X-ray spectra from the imaging spectrometer on board the Suzaku astronomical satellite. Baker et al (2019) analyzed in detail Hinode/EIS observations of plasma composition during the decay phase of an M-class flare in AR 11429. Patches of I-FIP effect plasma appeared in a highly sheared emerging flux region above sunspot umbrae 10 minutes after the flare peak and disappeared 40 minutes later.…”