Solar Physics and Plasma Physics: Topics and Advances

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: 31 August 2024 | Viewed by 10213

Special Issue Editors

Department of Physics and Chemistry, University of Palermo, 90127 Palermo, Italy
Interests: x-ray; solar physics; solar activity; hydrodynamics; magnetohydrodynamics; plasma physics; space physics; astronomy; astronomy & astrophysics astrophysics
Department of Physics and Chemistry, University of Palermo, 90127 Palermo, Italy
Interests: solar physics; space weather; magnetohydrodynamics; numerical simulations

Special Issue Information

Dear Colleagues,

The outer solar atmosphere, called the corona, is mysteriously at a million degrees and, therefore, it is a natural laboratory to study highly ionized plasma. Images taken in high energy bands from satellite missions reveal a strongly structured and dynamic environment where the bright plasma is confined and heated by the magnetic field. We see steadily bright active regions but also highly transient and explosive events, such as flares. There are also solar regions where the magnetic field opens toward the interplanetary space and releases the solar wind and other transient massive outflows, such as jets, solar eruptions and coronal mass ejections. These end up interacting with the circumterrestrial medium and, therefore, directly with human activities.

Mass acceleration and energy transport and release, both in closed and open magnetic structures, are challenging because they involve processes at different temporal and spatial scales at once; this is a state-of-the-art issue.

Dr. Fabio Reale
Dr. Paolo Pagano
Guest Editors

Manuscript Submission Information

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Keywords

  • Magnetic reconnection and particle acceleration
  • Magnetohydrodynamics of coronal plasma
  • MHD turbulence, waves and instabilities
  • Coronal loops and heating
  • Coronal flares, eruptions and ejections
  • Plasma MHD to kinetic scales

Published Papers (5 papers)

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Research

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25 pages, 4088 KiB  
Article
Asymmetric Twisting of Coronal Loops
Symmetry 2023, 15(3), 627; https://doi.org/10.3390/sym15030627 - 02 Mar 2023
Cited by 1 | Viewed by 805
Abstract
The bright solar corona entirely consists of closed magnetic loops rooted in the photosphere. Photospheric motions are important drivers of magnetic stressing, which eventually leads to energy release into heat. These motions are chaotic and obviously different from one footpoint to the other, [...] Read more.
The bright solar corona entirely consists of closed magnetic loops rooted in the photosphere. Photospheric motions are important drivers of magnetic stressing, which eventually leads to energy release into heat. These motions are chaotic and obviously different from one footpoint to the other, and in fact, there is strong evidence that loops are finely stranded. One may also expect strong transient variations along the field lines, but at a glance, coronal loops ever appear more or less uniformly bright from one footpoint to the other. We aim to understand how much coronal loops can preserve their own symmetry against asymmetric boundary motions that are expected to occur at loop footpoints. We investigate this issue by time-dependent 2.5D MHD modelling of a coronal loop, including its rooting and beta-variation in the photosphere. We assume that the magnetic flux tube is stressed by footpoint rotation but also that the rotation has a different pattern from one footpoint to the other. In this way, we force strong asymmetries because we expect independent evolution along different magnetic strands. We found that until the Alfvén crossing-travel time relative to the entire loop length is much lower than the twisting period, the loop’s evolution depends only on the relative velocity between the boundaries, and the symmetry is efficiently preserved. We conclude that the very high Alfvén velocities that characterise the coronal environment can explain why coronal loops can maintain a very high degree of symmetry even when they are subjected to asymmetric photospheric motions for a long time. Full article
(This article belongs to the Special Issue Solar Physics and Plasma Physics: Topics and Advances)
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13 pages, 1682 KiB  
Article
Temperature and Thermal Energy of a Coronal Mass Ejection
Symmetry 2022, 14(3), 468; https://doi.org/10.3390/sym14030468 - 25 Feb 2022
Cited by 4 | Viewed by 1429
Abstract
Due to the scarcity of UV–EUV observations of coronal mass ejections (CMEs) far from the Sun (i.e., at heliocentric distances larger than 1.5 Rsun) our understanding of the thermodynamic evolution of these solar phenomena is still very limited. This [...] Read more.
Due to the scarcity of UV–EUV observations of coronal mass ejections (CMEs) far from the Sun (i.e., at heliocentric distances larger than 1.5 Rsun) our understanding of the thermodynamic evolution of these solar phenomena is still very limited. This work focuses on the analysis of a slow CME observed at the same time and in the same coronal locations in visible light (VL) by the MLSO Mark IV polarimeter and in the UV Lyman-α by the SOHO UVCS spectrometer. The eruption was observed at two different heliocentric distances (1.6 and 1.9 Rsun), making this work a test case for possible future multi-slit observations of solar eruptions. The analysis of combined VL and UV data allows the determination of 2D maps of the plasma electron density and also the plasma electron temperature, thus allowing the quantification of the distribution of the thermal energy density. The results show that the higher temperatures in the CME front are due to simple adiabatic compression of pre-CME plasma, while the CME core has a higher temperature with respect to the surrounding CME void and front. Despite the expected adiabatic cooling, the CME core temperatures increased between 1.6 and 1.9 Rsun from 2.4 MK up to 3.2 MK, thus indicating the presence of plasma heating processes occurring during the CME expansion. The 2D distribution of thermal energy also shows a low level of symmetry with respect to the CME propagation axis, possibly related with the CME interaction with nearby coronal structures. This work demonstrates the potential of UV and VL data combination and also of possible future multi-slit spectroscopic observations of CMEs. Full article
(This article belongs to the Special Issue Solar Physics and Plasma Physics: Topics and Advances)
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9 pages, 314 KiB  
Article
Energetic Particle Superdiffusion in Solar System Plasmas: Which Fractional Transport Equation?
Symmetry 2021, 13(12), 2368; https://doi.org/10.3390/sym13122368 - 08 Dec 2021
Cited by 5 | Viewed by 2762
Abstract
Superdiffusive transport of energetic particles in the solar system and in other plasma environments is often inferred; while this can be described in terms of Lévy walks, a corresponding transport differential equation still calls for investigation. Here, we propose that superdiffusive transport can [...] Read more.
Superdiffusive transport of energetic particles in the solar system and in other plasma environments is often inferred; while this can be described in terms of Lévy walks, a corresponding transport differential equation still calls for investigation. Here, we propose that superdiffusive transport can be described by means of a transport equation for pitch-angle scattering where the time derivative is fractional rather than integer. We show that this simply leads to superdiffusion in the direction parallel to the magnetic field, and we discuss some advantages with respect to approaches based on transport equations with symmetric spatial fractional derivates. Full article
(This article belongs to the Special Issue Solar Physics and Plasma Physics: Topics and Advances)
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15 pages, 803 KiB  
Article
Solar Ultraviolet Bursts in the Joint Footpoints of Multiple Transition Region Loops
Symmetry 2021, 13(8), 1390; https://doi.org/10.3390/sym13081390 - 31 Jul 2021
Cited by 1 | Viewed by 1452
Abstract
Solar Ultraviolet bursts (UBs) associated with flux emergence are expected to help understand the physical processes of the flux emergence itself. In the present study, we analyse imaging and spectroscopic observations of a special group of UBs (including twelve of them) occurring in [...] Read more.
Solar Ultraviolet bursts (UBs) associated with flux emergence are expected to help understand the physical processes of the flux emergence itself. In the present study, we analyse imaging and spectroscopic observations of a special group of UBs (including twelve of them) occurring in the joint footpoint regions of multiple transition region loops above the flux emerging regions. Consistent with previous studies of common UBs, we found that the spectral characteristics of this group of UBs are varied. Our results show that the responses of UBs in Ni ii, NUV continuum, Mg ii h and O i are originated from locations differ from that emits Si iv. The imaging data show that UBs have connections with the dynamics in the transition region loops. Brightenings starting from UB-regions and propagating along loops can be seen in SJ 1400/1330 Å and AIA 304 Å images and the corresponding time-space images. The apparent velocities are tens of kilometers per second in AIA 304 Å. For symmetry, the brightenings can propagate from the UB-regions towards opposite directions with similar apparent velocities in some cases. Given that these UBs are magnetic reconnection phenomena, we suggest that the propagating brightenings are the signals of the plasma flows resulted from heatings in the UB-regions. Full article
(This article belongs to the Special Issue Solar Physics and Plasma Physics: Topics and Advances)
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Review

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23 pages, 3002 KiB  
Review
How Transverse Waves Drive Turbulence in the Solar Corona
Symmetry 2022, 14(2), 384; https://doi.org/10.3390/sym14020384 - 15 Feb 2022
Cited by 4 | Viewed by 2211
Abstract
Oscillatory power is pervasive throughout the solar corona, and magnetohydrodynamic (MHD) waves may carry a significant energy flux throughout the Sun’s atmosphere. As a result, over much of the past century, these waves have attracted great interest in the context of the coronal [...] Read more.
Oscillatory power is pervasive throughout the solar corona, and magnetohydrodynamic (MHD) waves may carry a significant energy flux throughout the Sun’s atmosphere. As a result, over much of the past century, these waves have attracted great interest in the context of the coronal heating problem. They are a potential source of the energy required to maintain the high-temperature plasma and may accelerate the fast solar wind. Despite many observations of coronal waves, large uncertainties inhibit reliable estimates of their exact energy flux, and as such, it remains unclear whether they can contribute significantly to the coronal energy budget. A related issue concerns whether the wave energy can be dissipated over sufficiently short time scales to balance the atmospheric losses. For typical coronal parameters, energy dissipation rates are very low and, thus, any heating model must efficiently generate very small-length scales. As such, MHD turbulence is a promising plasma phenomenon for dissipating large quantities of energy quickly and over a large volume. In recent years, with advances in computational and observational power, much research has highlighted how MHD waves can drive complex turbulent behaviour in the solar corona. In this review, we present recent results that illuminate the energetics of these oscillatory processes and discuss how transverse waves may cause instability and turbulence in the Sun’s atmosphere. Full article
(This article belongs to the Special Issue Solar Physics and Plasma Physics: Topics and Advances)
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