Article
Astronomy & Astrophysics
C. D. Johnston, A. W. Hood, I De Moortel, P. Pagano, T. A. Howson
Summary: The paper demonstrates the efficient formulation of the TRAC method for multi-dimensional MHD simulations, which does not rely on field line tracing but uses local cutoff temperatures instead of global cutoff temperatures. This approach successfully preserves the properties of the original TRAC method, including the conservation of total radiative losses and heating in the MHD formulation. Results from 2D MHD simulations show the versatility and robustness of the method in multi-dimensional magnetic fields.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
M. Pelekhata, K. Murawski, S. Poedts
Summary: In this paper, the two-fluid modeling of Alfven and magnetoacoustic waves in the partially ionized solar chromosphere is reexamined. Numerical simulations show that large-amplitude wave pulses can significantly increase the chromospheric temperature and result in faster plasma outflows.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Yajie Chen, Hardi Peter, Damien Przybylski, Hui Tian, Jiale Zhang
Summary: This study investigates Doppler shifts in a 3D radiation magnetohydrodynamic (MHD) model of the quiet Sun and compares them to observed properties. The model successfully reproduces the observed change of average net Doppler shifts from redshifted to blueshifted from the transition region into the corona.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
M. Skan, S. Danilovic, J. Leenaarts, F. Calvo, M. Rempel
Summary: Recent observations have found loop-like structures at small scales in the transition region and coronal temperatures, with unclear formation mechanism. This study investigates the occurrence of these features using realistic magnetohydrodynamic simulations and forward synthesis of spectral lines.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
R. Keppens, B. Popescu Braileanu, Y. Zhou, W. Ruan, C. Xia, Y. Guo, N. Claes, F. Bacchini
Summary: This article introduces the recent developments in the open-source MPI-AMRVAC code and demonstrates its application in astrophysics. Testing different schemes and modules showcases the flexibility and reliability of the code, while providing reproducible tests of all functionalities.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Yu-Hao Zhou, Wen-Zhi Ruan, Chun Xia, Rony Keppens
Summary: The study aims to extend the adaptive conduction method to fully multidimensional magnetohydrodynamic settings for realistic applications in solar atmosphere simulations. Two strategies are proposed and demonstrated in 2D simulations, showing promising results in addressing the underestimated chromospheric evaporation due to poor spatial resolution in the transition region.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Mats Carlsson, Lyndsay Fletcher, Joel Allred, Petr Heinzel, Jana Kasparova, Adam Kowalski, Mihalis Mathioudakis, Aaron Reid, Paulo J. A. Simoes
Summary: The aim of this study is to provide realistic simulations of a flaring loop, with a focus on the detailed treatment of the chromospheric energy balance. By comparing existing and upcoming observations with synthetic observables from the simulations, the complex interactions in a flaring chromosphere can be elucidated.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Abbas Raboonik, Paul S. Cally
Summary: A 2.5D numerical model of magnetoacoustic-Alfven linear mode conversions in the partially ionized low solar atmosphere induced by the Hall effect is surveyed. It is found that the Hall effect has a significant impact on the conversion between magnetoacoustic and Alfven waves, especially in the low chromosphere.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Yuji Kotani, T. T. Ishii, D. Yamasaki, K. Otsuji, K. Ichimoto, A. Asai, K. Shibata
Summary: This study investigates the thermal properties of small flares in the quiet Sun through imaging spectroscopic and imaging observations. The results show that more than half of the small flares exhibit a redshift and line center brightening in the Ha line, and the differential emission measure analysis confirms the consistency with the scaling law. The temporal evolution of temperature and density suggests that chromospheric evaporations/condensations play a significant role in the thermal properties of small flares, similar to large flares.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
A. Prasad, S. Kumar, A. C. Sterling, R. L. Moore, G. Aulanier, R. Bhattacharyya, Q. Hu
Summary: In this study, a magnetohydrodynamic simulation of active region NOAA 12241 was performed to understand the formation and evolution of a magnetic flux rope during the onset of an M6.9 flare. The simulation supports the development of the magnetic flux rope through tether-cutting magnetic reconnection inside the sheared coronal arcade. The eruptive nature of the magnetic flux rope is attributed to its formation in a torus-unstable region and runaway tether-cutting reconnection.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
M. K. Druett, J. Leenaarts, M. Carlsson, M. Szydlarski
Summary: This study examines the movements of mass elements within dense fibrils in order to understand the processes of fibril creation and destruction. The results show the main process of fibrilar loading and suggest additional plausible scenarios.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Physics, Multidisciplinary
Chaowei Jiang, Jun Chen, Aiying Duan, Xinkai Bian, Xinyi Wang, Jiaying Li, Peng Zou, Xueshang Feng
Summary: This study reveals the formation and evolution of MFRs during CME eruptions, as well as the impact of magnetic reconnection on MFRs through MHD simulations. The findings show that MFR gradually separates from the ambient field through reconnection via QSL, and experiences reconnection within the MFR in the later stages of the eruption, leading to a decrease in toroidal magnetic flux.
FRONTIERS IN PHYSICS
(2021)
Article
Physics, Multidisciplinary
Zhenjun Zhou, Chaowei Jiang, Xiaoyu Yu, Yuming Wang, Yongqiang Hao, Jun Cui
Summary: Solar eruptions display rotation of filaments, which can be caused by either external shear-field torque or internal magnetic twist relaxation. It is difficult to determine the dominant contribution from direct observations. In this study, a full MHD simulation of solar eruption was used to investigate the mechanism of magnetic flux rope rotation. The simulation suggests that the external shear-field torque plays a major role in the counterclockwise rotation, while the Lorentz torque inside the flux rope has a negative effect on it.
FRONTIERS IN PHYSICS
(2023)
Article
Astronomy & Astrophysics
M. Cecere, A. Costa, T. Van Doorsselaere
Summary: The study aims to investigate the characteristics of gyrosynchrotron (GS) radiation in fast sausage modes, specifically the intensity, modulation depth, and mean modulation depth as a function of frequency and line of sight (LOS). By solving the ideal 2.5D magnetohydrodynamics (MHD) equations for a straight coronal loop with chromosphere and typical flaring plasma parameters, the wavelet transform of density and GS emission was analyzed under different radio frequencies and spatial resolutions. The results showed that fast fundamental sausage modes with a first harmonic mode can be reproduced in radio emission, and the modulation depth was found to increase with higher radio frequencies and larger LOS angles.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Rebecca A. Robinson, Mats Carlsson
Summary: Numerical models can provide context to observations of nanoflare-scale reconnection events and help determine the details of these events. Detecting and understanding the mechanisms behind small-scale reconnection events is crucial for studying solar activity.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
J. Reid, P. J. Cargill, C. D. Johnston, A. W. Hood
Summary: A method is presented to use heating input determined by a 3D MHD model for coronal heating in field-aligned 1D hydrodynamic models. The method yields results of temperature and density variations along field lines, but asymmetries in plasma flow caused by the heating function can be observed.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
C. D. Johnston, A. W. Hood, I De Moortel, P. Pagano, T. A. Howson
Summary: The paper demonstrates the efficient formulation of the TRAC method for multi-dimensional MHD simulations, which does not rely on field line tracing but uses local cutoff temperatures instead of global cutoff temperatures. This approach successfully preserves the properties of the original TRAC method, including the conservation of total radiative losses and heating in the MHD formulation. Results from 2D MHD simulations show the versatility and robustness of the method in multi-dimensional magnetic fields.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
T. A. Howson, I. De Moortel, D. I. Pontin
Summary: The study shows that the magnetic Kelvin-Helmholtz instability can trigger magnetic reconnection and enhance the dissipation rate of energy stored in the magnetic field in the solar corona. Magnetic reconnection tends to occur along the boundaries of Kelvin-Helmholtz vortices, and the rate decreases with a reduction in the growth rate of KHI.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
L. E. Fyfe, T. A. Howson, I. De Moortel, V. Pant, T. Van Doorsselaere
Summary: Studies have found that the ratio between non-thermal line widths and root mean squared wave amplitudes varies across different simulations due to factors such as line-of-sight angles, velocity magnitudes, wave interference, and exposure time. Therefore, the widely used method for estimating wave energy is not robust.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Bart De Pontieu, Paola Testa, Juan Martinez-Sykora, Patrick Antolin, Konstantinos Karampelas, Viggo Hansteen, Matthias Rempel, Mark C. M. Cheung, Fabio Reale, Sanja Danilovic, Paolo Pagano, Vanessa Polito, Ineke De Moortel, Daniel Nobrega-Siverio, Tom Van Doorsselaere, Antonino Petralia, Mahboubeh Asgari-Targhi, Paul Boerner, Mats Carlsson, Georgios Chintzoglou, Adrian Daw, Edward DeLuca, Leon Golub, Takuma Matsumoto, Ignacio Ugarte-Urra, Scott W. McIntosh
Summary: The Multi-slit Solar Explorer (MUSE) is a proposed mission that aims to provide unprecedented spectral and imaging diagnostics of the solar corona. MUSE will use its innovative multi-slit design to obtain spectra in multiple spectral bands simultaneously, allowing for the study of the dynamic evolution of the coronal plasma. The mission will shed light on the mechanisms behind coronal heating.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
F. Moreno-Insertis, D. Nobrega-Siverio, E. R. Priest, A. W. Hood
Summary: This study aims to calculate a set of theoretical self-similar solutions to the nonlinear diffusion equation with cylindrical symmetry, which can be used as tests for MHD codes incorporating ambipolar diffusion. The theoretical solutions are obtained using mathematical methods and are validated using the Bifrost code. The results show that the Bifrost code can reproduce the theoretical solutions with sufficient accuracy and can be used to test the performance of MHD codes.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
T. A. Howson, I De Moortel
Summary: This study investigates the atmospheric response to coronal heating driven by random velocity fields with different characteristic time scales and amplitudes. The results reveal that direct current (DC) driving leads to greater energy injection and higher temperatures compared to alternating current (AC) driving. AC driving results in more frequent but shorter duration energy release events, leading to asymmetric temperature profiles. Higher velocity driving is associated with larger currents, higher temperatures, and a larger corona volume. The majority of heating is associated with small energy release events.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
D. J. Pascoe, T. Van Doorsselaere, I De Moortel
Summary: We study the use of propagating kink waves as a diagnostic technique. The transverse structuring of the plasma can be inferred by the frequency-dependent wave damping. However, the classical model significantly overestimates the damping rate in coronal loops with low density contrast ratios.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
D. J. Pascoe, I De Moortel, P. Pagano, T. A. Howson
Summary: This study considers the behavior of Alfven waves propagating in a medium with random density perturbations. The interaction between the Alfven waves and the medium generates reflections most efficiently when their wavelength is comparable to the spatial scale of the density perturbations. This leads to the generation of quasi-periodic oscillations, and the periods of oscillation are no longer solely associated with the driver. Multiple wave reflections cause oscillatory power to be retained at low altitudes, increasing opportunities for heating at those locations.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
I. De Moortel, T. A. Howson
Summary: The long-standing question of why the Sun's atmosphere is much hotter than its surface is investigated in this study, along with the potential role of magnetohydrodynamic waves. Through 3D MHD simulations, the researchers found that wave heating associated with resonant driving can balance radiative losses in the coronal loop, while nonresonant driving or higher density loops lead to cooling.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
J. Reid, J. Threlfall, A. W. Hood
Summary: Straightened cylindrical models of coronal loops have been commonly used to study heating processes, but the influence of geometric curvature on the heating has not been thoroughly examined. This study compares the heating and associated mechanisms in straightened models with those in curved loops. The analysis reveals bursty and aperiodic nanoflares resulting from processes initially triggered by magnetic reconnection, which are evenly distributed throughout the corona with a slight bias away from the footpoints. The independent occurrence of nanoflare-like events at separate sites along individual strands is an interesting finding.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
G. Cozzo, J. Reid, P. Pagano, F. Reale, A. W. Hood
Summary: In this study, we used three-dimensional MHD simulations to explore the interaction of magnetic flux tubes in a stratified atmosphere. Our results show that avalanches can occur in realistic conditions and can result in the release of magnetic energy as a result of photospheric motions.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Simon Daley-Yates, Moira M. Jardine, Craig D. Johnston
Summary: Recent observations have found asymmetries in the H alpha line of rapidly rotating cool dwarfs, indicating the presence of clumps of cool, dense plasma in the stars' coronae. These clumps may persist for a long time or be dynamically ejected from the star. Magnetohydrodynamic simulations of a young, rapidly rotating Sun have shown that excess surface heating triggers the formation of these condensations, which exhibit quasi-periodic behavior and fall back towards the surface. These simulations also suggest that coronal rain may be common in solar-like stars, but appear on larger scales in rapid rotators.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Physics, Multidisciplinary
Thomas Howson, Ineke De Moortel
Summary: Recent studies have shown that coronal wave heating can balance radiative losses in low-density loops undergoing resonant absorption, phase mixing, and the Kelvin-Helmholtz instability. Broadband and multi-directional drivers with resonant and non-resonant frequencies were considered. Three-dimensional magnetohydrodynamic simulations were used to impose continuous velocity drivers on the footpoints of a dense coronal loop. The results indicated that the energy dissipation rates from the wave drivers are sufficient to balance average energy losses, but the loop core still cools due to local insufficiency in wave heating rates.