RoCS scientists publications January 2021

1. Excitation and evolution of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere

Journal: Astronomy and Astrophysics

1^st Author:  Petra Kohutova

Position: Postdoc

Co-authors from RoCS: 

• Andrius Popovas

Short summary by the author

We have analysed excitation and evolution of coronal oscillations in the Bifrost enhanced network simulation. We have combined forward modelling of EUV emission with 3D magnetic field tracing to do this. We have found that coronal oscillations are abundant in Bifrost simulations, and that the wave regimes in the simulation match those seen in real solar observations. We conclude that the self-consistent simulations can be used as a laboratory for studying oscillation excitation, evolution and damping in realistic solar atmosphere.

2. Signatures of ubiquitous magnetic reconnection in the deep atmosphere of sunspot penumbrae

Journal: Astronomy and Astrophysics

1^st Author: Luc Rouppe van der Voort

Position: Professor

Co-authors from RoCS: 

• Jayant Joshi
• Vasco Manuel de Jorge Henriques
• Souvik Bose

Short summary by the author

We used high-quality observations from the Swedish 1-m Solar Telescope on La Palma to show that magnetic reconnection is a very common process in the penumbra of sunspots. We observed large numbers of so-called Ellerman Bombs in the penumbra of several different sunspots. Ellerman Bombs are markers of magnetic reconnection in the low solar atmosphere and were known to exist in the sunspot penumbra, but not in the large numbers that we report here. These new observations are of great interest for new and upcoming 4-m class telescopes such as the American DKIST and European Solar Telescope (EST) since these penumbral Ellerman Bombs may represent the smallest observable reconnection events on the Sun. 

3. Downflowing umbral flashes as an evidence of standing waves in sunspot umbrae

Journal: Astronomy and Astrophysics

1^st Author: T. Felipe, Instituto de Astrofísica de Canarias

Position: Researcher

Co-authors from RoCS: 

• Vasco Manuel de Jorge Henriques

Short summary by the author

The mesmerizing umbral flashes, periodic 3-min strong brightenings of the darkest region of sunspots, have recently been shown to harbour strong downflows (km per second) by RoCS scientists. In this work, in a collaboration with scientists from the Canary Islands and from Stockholm, we have found that resonant cavities, like those present in a musical instrument, will naturally lead to strong downflows in the upper layers of sunspots' atmospheres as part of the brightening process. This result is a piece of the puzzle that has been missing and is a surprising outcome from simulations that beautifully meets recent surprising observations. It provides us with fundamental understanding of umbral flash formation and the remarkable physics of sunspots.

4.Spicules and downflows in the solar chromosphere

Journal: Astronomy and Astrophysics

1^st Author: Souvik Bose

Position: Doctoral Research Fellow

Co-authors from RoCS: 

• Jayant Joshi
• Vasco Manuel de Jorge Henriques
• Luc Rouppe van der Voort

Short summary by the author

Plasma downflows in the solar atmosphere are abundant, especially in the solar transition region and the lower solar corona. Despite their abundance higher up in the Sun’s atmosphere, it has been hard to find their signatures in the deeper layers such as the chromosphere. In this study, we targeted an enhanced network region with the Swedish 1-m Solar Telescope on La Palma that shows ample occurrences of rapid downflows, in the chromospheric H-alpha spectral line, in the form of spicules. These spicular downflowing features have been characterized for the first time in conjunction with the well-known rapid blue-shifted and red-shifted excursions (RBEs and RREs), and have been termed as downflowing RREs.  Contrary to the traditional RREs, the downflowing RREs are associated with chromospheric field-aligned downflows moving toward the strong magnetic field regions with an oppositely directed plane-of-sky motion. These observations are interesting because they could well be the chromospheric counterparts of the transition region downflows and can help us to investigate the mass and energy cycling process between the chromosphere and the corona.