Evolution of the Ratio of Mg II Intensities During Solar Flares

Abstract

The Mg II k \& h line intensity ratios can be used to probe the characteristics of the plasma in the solar atmosphere. In this study, using the observations recorded by the Interface Region Imaging Spectrometer (IRIS), we study the variation of the Mg II k \& h intensity ratio for three flares belonging to X-class, M-class, and C-class, throughout their evolution. We also study the k-to-h intensity ratio as a function of magnetic flux density obtained from the line-of-sight magnetograms recorded by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Our results reveal that while the intensity ratios are independent of magnetic flux density, they show significant changes during the evolution of the C-class and M-class flares. The intensity ratios start to increase at the start of the flare and peak during the impulsive phase before the flare peak and decrease rapidly thereafter. The values of the ratios fall even below the pre-flare level during the peak and decline phases of the flare. These results are important in light of the heating and cooling of localized plasma and provide further constraints on the understanding of flare physics.

arXiv commentAccepted for publication in ApJ

References in corpus (17)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• The Interface Region Imaging Spectrograph (IRIS)
• The formation of IRIS diagnostics II. The formation of the Mg II h&k lines in the solar atmosphere
• The formation of IRIS diagnostics I. A quintessential model atom of Mg II and general formation properties of the Mg II h&k lines
• The formation of IRIS diagnostics. III. Near-ultraviolet Spectra and Images
• The Radiated Energy Budget of Chromospheric Plasma in a Major Solar Flare Deduced From Multi-Wavelength Observations
• The Formation of IRIS diagnostics. IV. The Mg II triplet lines as a new diagnostic for lower chromospheric heating
• Identifying typical Mg II flare spectra using machine learning
• IRIS Observations of the Mg II h & k Lines During a Solar Flare
• Solar Flare Ribbon Fronts I: Constraining flare energy deposition with IRIS spectroscopy
• Modelling of Mg II lines in solar prominences
• Exploring mutual information between IRIS spectral lines. II. Calculating the most probable response in all spectral windows
• Flare Ribbons Approach Observed by the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory
• On the Bright Loop Top Emission in Post Eruption Arcades
• Irreversible Rapid Changes of Magnetic Field Associated with the 2012 October 23 Circular Near-limb X1.8 Flare
• Solar radio burst associated with the falling bright EUV blob