Transient inverse-FIP plasma composition evolution within a confined solar flare
2019
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.
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