Evolution of Transient Inverse FIP Composition in a Solar Flare

Elemental abundance variations of solar and stellar coronae have mainly been linked to the surface temperatures of stars. Recent spatially resolved observations provided by Hinode/EIS combined with SDO/AIA and HMI indicate that magnetic activity has a role to play, too. Coronae of solar-type stars are over-abundant in elements which have low first ionisation potential (FIP), while cooler M dwarfs, which have large starspots and produce giant flares, have coronae which are under-abundant in such elements (inverse FIP or IFIP abundance). Using Hinode/EIS data, we analyze the spatial and temporal evolution of elemental abundances in a solar flare in a newly emerging, highly sheared active region (NOAA11429). We find overall FIP-effect dominated composition in the emerging active region, but we also find anomalous (IFIP) composition plasma in localized patches. During the decay phase of the flare, patches above the flare ribbons evolve from FIP to IFIP abundances, while the flaring loop tops show an enhanced FIP composition. The patch and loop compositions then evolve toward the pre-flare state. We propose an explanation of how sub-photospheric reconnection can result in IFIP plasma composition over coalescing umbrae. On the basis of the magnetic field evolution, we argue that subsurface reconnection between the coalescing umbrae leads to the depletion of low-FIP elements as a result of an increased fast-mode 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-composition plasma. IFIP composition may be more frequent or even the dominant composition signature on M-stars with a high filling factor of starspots and giant flares.