The composition of the solar corona and the solar wind often differs from that of the solar photosphere, typically with a relative enrichment of elements with low first ionization potential (FIP…

The Smithsonian Institution, through its Smithsonian Astrophysical Observatory division, has been awarded a $524,986 grant by the National Aeronautics and Space Administration Shared Services Center. The grant will fund research to analyze coordinated spectroscopic observations from NASA's Interface Region Imaging Spectrograph and Hinode/EUV Imaging Spectrometer instruments of solar active regions over at least one week. The research aims to measure the low first ionization potential effect in active regions at high spatial and temporal resolution to determine how elemental fractionation observed in the outer solar atmosphere correlates with plasma properties in the lower atmosphere over the course of active region evolution. The results will provide novel observational constraints on modeling of chemical fractionation processes in the solar outer atmosphere and address science goals of the IRIS and Hinode missions regarding mass and energy flows. No set-aside designation was used for this award made under the grant's April 1, 2021 effective date and March 31, 2025 period of performance.

The composition of the solar corona and the solar wind often differs from that of the solar photosphere, typically with a relative enrichment of elements with low first ionization potential (FIP effect). This chemical fractionation is poorly understood but IT can provide crucial clues about the physical processes at work in the solar outer atmosphere: surely originating in the chromosphere where the first ionization occurs, and linked to the coronal heating mechanism, but carrying its signature throughout the many layers and magnetic structuring of the corona and into the solar wind. The variation of the chemical fractionation, both in space and in time, can therefore be used as a tracer of the mass and energy flow throughout the solar atmosphere. Studies of temporal variations of the elemental abundances using skylab data hinted at a systematic increase of low-FIP elements enhancement (up to almost an order of magnitude) in an active region (AR) over about 7 days [1]. Only a couple of more recent studies have investigated the temporal variations of FIP in ARS and suggested a more complex relationship with AR age [2,3], warranting more extensive analyses. We propose to use current spectroscopic observations with iris and hinode/EIS, covering from the chromosphere to the transition region (TR) and the corona, to measure the FIP effect in ARS at high spatial resolution, with cadence of a few hours (or higher), and over at least a week, in order to cover a significant portion of the AR evolution. We will combine coronal spectra with TR and chromospheric spectra to reveal possible correlations between the chemical fractionation observed in the outer solar atmosphere with plasma properties in the lower atmosphere (e.g., non-thermal broadening). A large number of coordinated hinode-iris observations suitable for this type of study are publicly available, including for instance the iris-hinode observing plan 307, which has already yielded limb-to-limb monitoring (several hours a day) of several ARS. We will analyze the optically thin EIS spectral data using FIP diagnostics based on single line fits (as in [2,3]), and also by using a new inversion method [4], which infers the plasma emission measure and velocity distribution as a function of temperature. We will modify this inversion algorithm to include element abundances as one of the inverted parameters, and consistently derive coronal abundances (together with the thermal distribution, the velocity, and non-thermal broadening) for a large set of AR spectral observations. We will also apply IRIS2 inversions to the optically thick MG II h & k lines, a novel database based on machine and deep learning techniques that allows the inference of the thermodynamic conditions of the lower atmosphere from iris spectra by taking into account non- LTE conditions in the chromosphere [5]. These unique measurements and application of state-of-the-art inversion codes will allow US to derive chemical fractionation and connect IT to observables such as flows, thermal and non-thermal broadening throughout the solar atmosphere, as a function of the AR evolution and center to limb variations. These results will determine whether or how these variations are related to conditions in the chromosphere, where the FIP effect is thought to originate, and, in turn, will provide novel and much-needed observational constraints on modeling and theory of chemical fractionation [6] than so far available. Our investigation will provide unique constraints on chemical fractionation and address some of the main goals of the iris and hinode missions, such as understanding the mass and energy flows in the solar outer atmosphere. The elemental abundance of solar wind streams is also the best-known discriminator between various states of the wind consequently, the proposed study is also of great interest in in-situ observations such as solar orbiter and PSP.