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Continuum Enhancements, Line Profiles, and Magnetic Field Evolution during Consecutive Flares

Papers from SWICo members

Zuccarello, Francesca; Guglielmino, Salvo L.; Capparelli, Vincenzo; Mathioudakis, Mihalis; Keys, Peter H.; Criscuoli, Serena; Falco, Mariachiara; Murabito, Mariarita

The occurrence of very energetic solar flares can give rise to Space Weather phenomena impacting on the circum-terrestrial environment.It is well known that, during solar flares, magnetic energy can be converted into electromagnetic radiation from radio waves to γ-rays. Enhancements in the continuum at visible wavelengths, as well as continuum enhancements in the FUV and NUV passbands, give rise to the so-called white-light (WL) flares. Moreover, the strong energy release taking place during these events can lead to the rearrangement of the magnetic field at the photospheric level, causing morphological changes in sunspots.

Left: Map showing the details of the δ-spot hosting the flares (the arrow indicates the WL ribbon). The blue, orange, and green circles indicate the IRIS slit positions used to determine the line profiles shown on the Right for Si IV 140.28 nm (top row) and C II 133.575 nm (bottom row). In each row, the line profiles for successive times are overplotted on the relevant spectrograms. The dashed vertical lines indicate the position of the line center, while the blue, orange, and green circles show the slit positions relative to the profiles indicated with the same colors.

In this paper, we describe the results of the analysis performed using data acquired by satellite instruments (Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Hinode/Solar Optical Telescope) and ground-based telescopes (Rapid Oscillations in the Solar Atmosphere (ROSA)/Dunn Solar Telescope) during two consecutive C7.0 and X1.6 flares (accompanied by an eruption) that occurred in active region NOAA 12205 on 2014 November 7. The analysis shows the presence of continuum enhancements during the evolution of the events, observed both in ROSA images and in IRIS spectra. We also investigate the role played by the evolution of the δ sunspots in the flare triggering, as well as the changes in the penumbrae surrounding these sunspots as a further consequence of these flares.

Publication: Zuccarello F., Guglielmino S. L., Capparelli V., Mathioudakis M., Keys P. H., Criscuoli S., Falco M., et al., 2020, ApJ, 889, 65. doi:10.3847/1538-4357/ab621f

Can superflares occur on our Sun?

Papers from SWICo members


Paolo Romano, Abouazza Emhamdi, Ayman Kordi

Two strong homologous white light flares of X-GOES class occurred on the Sun on Sept. 06, 2017, providing a rare exceptional opportunity to study the mechanisms responsible for the formation of the magnetic field configurations suitable for the manifestation of such yet enigmatic eruptive events and their effects in the lower layers of the solar atmosphere.

Using photospheric vector magnetograms, taken before the beginning of the two X-class events, as boundary conditions to reconstruct the non−linear coronal magnetic field configuration, we identified two related 3D null points located at low heights above the photosphere (i.e. in very low corona). These null points are most likely responsible for the triggering of the two strong X-GOES class flares. We deduced that their formation at such low altitudes may plausibly be ascribed to the peculiar photospheric horizontal motions of the main magnetic structures of the hosting Active Region NOAA 12673.

These events can be adopted as a hint for a possible interpretation of the activity of young G-type stars, recently reported by the Kepler mission, and can shed light on the probability that superflares occur on our Sun.

Publication: Two Strong White-Light Solar Flares in AR NOAA 12673 as Potential Clues for Stellar Superflares, Solar Physics, 294, 4, 2019