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  • 1. Schmit, D.
    et al.
    Bryans, P.
    De Pontieu, B.
    McIntosh, S.
    Leenaarts, Jorrit
    Stockholm University, Faculty of Science, Department of Astronomy.
    Carlsson, M.
    OBSERVED VARIABILITY OF THE SOLAR Mg II h SPECTRAL LINE2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 811, no 2, article id 127Article in journal (Refereed)
    Abstract [en]

    The Mg II h&k doublet are two of the primary spectral lines observed by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These lines are tracers of the magnetic and thermal environment that spans from the photosphere to the upper chromosphere. We use a double-Gaussian model to fit the Mg II h profile for a full-Sun mosaic data set taken on 2014 August 24. We use the ensemble of high-quality profile fits to conduct a statistical study on the variability of the line profile as it relates the magnetic structure, dynamics, and center-to-limb viewing angle. The average internetwork profile contains a deeply reversed core and is weakly asymmetric at h2. In the internetwork, we find a strong correlation between h3 wavelength and profile asymmetry as well as h1 width and h2 width. The average reversal depth of the h3 core is inversely related to the magnetic field. Plage and sunspots exhibit many profiles that do not contain a reversal. These profiles also occur infrequently in the internetwork. We see indications of magnetically aligned structures in plage and network in statistics associated with the line core, but these structures are not clear or extended in the internetwork. The center-to-limb variations are compared to predictions of semi-empirical model atmospheres. We measure a pronounced limb darkening in the line core that is not predicted by the model. The aim of this work is to provide a comprehensive measurement baseline and preliminary analysis on the observed structure and formation of the Mg II profiles observed by IRIS.

  • 2. van der Voort, L. Rouppe
    et al.
    De Pontieu, B.
    Scharmer, Göran B.
    Stockholm University, Faculty of Science, Department of Astronomy. The Royal Swedish Academy of Sciences, Sweden.
    de la Cruz Rodríguez, Jaime
    Stockholm University, Faculty of Science, Department of Astronomy.
    Martínez-Sykora, J.
    Nóbrega-Siverio, D.
    Guo, L. J.
    Jafarzadeh, S.
    Pereira, T. M. D.
    Hansteen, V. H.
    Carlsson, M.
    Vissers, Gregal
    Stockholm University, Faculty of Science, Department of Astronomy.
    Intermittent Reconnection and Plasmoids in UV Bursts in the Low Solar Atmosphere2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 851, no 1, article id L6Article in journal (Refereed)
    Abstract [en]

    Magnetic reconnection is thought to drive a wide variety of dynamic phenomena in the solar atmosphere. Yet, the detailed physical mechanisms driving reconnection are difficult to discern in the remote sensing observations that are used to study the solar atmosphere. In this Letter, we exploit the high-resolution instruments Interface Region Imaging Spectrograph and the new CHROMIS Fabry Perot instrument at the Swedish 1-m Solar Telescope (SST) to identify the intermittency of magnetic reconnection and its association with the formation of plasmoids in socalled UV bursts in the low solar atmosphere. The Si IV 1403 angstrom UV burst spectra from the transition region show evidence of highly broadened line profiles with often non-Gaussian and triangular shapes, in addition to signatures of bidirectional flows. Such profiles had previously been linked, in idealized numerical simulations, to magnetic reconnection driven by the plasmoid instability. Simultaneous CHROMIS images in the chromospheric Ca 11 K 3934 angstrom line now provide compelling evidence for the presence of plasmoids by revealing highly dynamic and rapidly moving brightenings that are smaller than 0.12 and that evolve on timescales of the order of seconds. Our interpretation of the observations is supported by detailed comparisons with synthetic observables from advanced numerical simulations of magnetic reconnection and associated plasmoids in the chromosphere. Our results highlight how subarcsecond imaging spectroscopy sensitive to a wide range of temperatures combined with advanced numerical simulations that are realistic enough to compare with observations can directly reveal the small-scale physical processes that drive the wide range of phenomena in the solar atmosphere.

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