Comparison of Solar Fine Structure Observed Simultaneously in Ly-α and Mg II h

Abstract

The Chromospheric Lyman Alpha Spectropolarimeter (CLASP) observed the Sun in H I Lyman-α during a suborbital rocket flight on September 3, 2015. The Interface Region Imaging Telescope (IRIS) coordinated with the CLASP observations and recorded nearly simultaneous and co-spatial observations in the Mg II h&k lines. The Mg II h and Ly-α lines are important transitions, energetically and diagnostically, in the chromosphere. The canonical solar atmosphere model predicts that these lines form in close proximity to each other and so we expect that the line profiles will exhibit similar variability. In this analysis, we present these coordinated observations and discuss how the two profiles compare over a region of quiet sun at viewing angles that approach the limb. In addition to the observations, we synthesize both line profiles using a 3D radiation-MHD simulation. In the observations, we find that the peak width and the peak intensities are well correlated between the lines. For the simulation, we do not find the same relationship. We have attempted to mitigate the instrumental differences between IRIS and CLASP and to reproduce the instrumental factors in the synthetic profiles. The model indicates that formation heights of the lines differ in a somewhat regular fashion related to magnetic geometry. This variation explains to some degree the lack of correlation, observed and synthesized, between Mg II and Ly-α. Our analysis will aid in the definition of future observatories that aim to link dynamics in the chromosphere and transition region.

arXiv commentAccepted by ApJ

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• Three-dimensional modeling of chromospheric spectral lines in a simulated active region
• The Response of the Lyman-Alpha Line in Different Flare Heating Models
• The dynamic chromosphere: pushing the boundaries of observations and models
• SunnyNet: A neural network approach to 3D non-LTE radiative transfer
• Effects of the chromospheric Lyα line profile shape on the determination of the solar wind HI outflow velocity using the Doppler dimming technique
• Spicules in IRIS Mg II Observations: Automated Identification
• Irregular grids for 3D NLTE radiative transfer in stellar atmospheres