Numerical simulations based on 3D MHD models have been used create and sustain a hot upper atmosphere of the Sun for various solar features, e.g. quiet Sun, bright points, or active regions. These models provide self-consistent explanations for quite a range of observational features e.g. for Ellerman bombs or UV bursts. They allow to follow the changes of the magnetic field, e.g. while field...
The High-Resolution Coronal Imager (Hi-C) instrument has been launched twice from White Sands Missile Range, each time capturing the highest resolution coronal images ever obtained, first in the 193 Angstrom passband and then in the 171 Angstrom passband. These two rocket flights, which collectively have yielded only 10 minutes of data, have generated over 80 refereed publications. In this...
Chaotic photospheric motions progressively shuffle and braid the magnetic field confining plasma in coronal loops. The stressed field can suddenly lose equilibrium and develop instabilities, candidate to release magnetic energy into heat. There is long experience in modeling impulsive energy releases in coronal loops, from a purely hydrodynamic approach (e..g.,Reale+2000,Testa&Reale2020), to a...
The dynamical evolution of the solar magnetic field(s) is a key ingredient in understanding the ubiquitous observed activity in the Sun. A fundamental process, which is responsible for this dynamical evolution, is the emergence of magnetic flux from the solar interior to the outer solar atmosphere. The cost of running realistic numerical models is no longer prohibitive in studying the rising...
The Sun’s atmosphere is powered by the complex convective motions which continuously churn the solar surface and stress the atmospheric magnetic field. However, describing the specifics of the resulting energy cycle, including the processes which ultimately drive energy dissipation and atmospheric heating remains a significant challenge. With this in mind, the community is continuously...
The MUSE instrument will provide information on intensity and flows in the corona with unprecedented spatial and temporal resolutions. High-resolution 3D MHD models of coronal loops are thus timely and crucial to investigate the connection between heating events and resulting spectral diagnostics.
We carried out high-resolution simulations of a straightened coronal loop that is...
Coronal Bright Points (CBPs) are ubiquitous structures in the solar atmosphere composed of hot small-scale loops observed in EUV or X-Rays. They are key elements to understand the heating of the corona; nonetheless, basic questions regarding their energization, heating mechanisms, the chromosphere underneath, or the effects of
flux emergence in these structures remain open.
We have used...
In recent years, a renaissance has occurred for wave heating mechanisms,
because of the plethora of wave observations in the corona since 10-20 years. This renewed interest in wave heating modelling has brought models from the 1D and cartoon level to full 3D wave heating models. It has been realised that the waves naturally induce the formation of small scales through turbulence, leading to...
The solar corona is shaped and mysteriously heated to millions of degrees by the Sun’s magnetic field. It has long been hypothesised that the heating results from a myriad of tiny magnetic energy outbursts called nanoflares, driven by the fundamental process of magnetic reconnection. This theory recently received significant support through the observational discovery of nanojets - very fast...
High-resolution, high-cadence EUV observations over the past decade have led to the discovery of a decay-less regime of kink oscillations in coronal loops. The means of excitation and sustaining such oscillations over many wave periods against energy dissipation mechanisms such as phase mixing and turbulence is still an unknown. Therefore, identifying the true nature of these decay-less...
I will discuss how high resolution current and future observations of the solar atmosphere (e.g., with IRIS, SDO, Hinode, MUSE and EUVST), help us advance our understanding of the role of different physical processes -- including, e.g., braiding, Alfven waves, accelerated particles resulting from magnetic reconnection -- in heating the solar corona.. In particular I will focus on the synergy...
Relaxation of braided coronal magnetic fields through reconnection is thought to be a source of energy to heat plasma in active region coronal loops. However, observations of active region coronal heating associated with untangling of magnetic braids remain sparse. One reason for this paucity could be the lack of coronal observations with sufficiently high spatial and temporal resolution to...
It remains unclear which physical processes are responsible for the dramatic increase with height of the temperature in stellar atmospheres, known as the chromospheric ($\sim$10,000 K) and coronal (several million K) heating problems. Statistical studies of sun-like stars reveal that chromospheric and coronal emissions are correlated on a global scale, constraining, in principle, theoretical...
The majority of the Sun is covered by a system of relatively weak magnetic fields called the Quiet Sun (QS) which, despite being far weaker than active regions, plays an important role in energizing the solar atmosphere. With new generations of simulations and instrumentation, it is becoming feasible to understand the dynamics of the QS with more precision than before. Using Bifrost, we have...
I will present recent additions to -- and applications of -- our open-source MPI-AMRVAC software (http://amrvac.org), designed to solve generic partial differential equations on any-dimensional, block grid-adaptive mesh hierarchies [2018, ApJS 234, 30 ; 2021, CaMWa 81, 316]. The MPI-AMRVAC 3.0 release is ready to go, and features various modules of direct interest to solar physicists, such as...
A major coronal heating theory based on magnetic reconnection relies on the existence of braided magnetic field structures in the corona, where numerical simulations of stress-induced reconnection in braided loop-like structures have shown to invariably lead to low-amplitude transverse MHD waves. In this small-angle reconnection scenario, the reconnected magnetic field lines are driven...
Data-constrained magnetohydrodynamics (MHD) simulations initialised with magnetic field extrapolations based on photospheric magnetograms have been quite successful in capturing many aspects of energetic events in the solar corona, like flare reconnections and coronal mass ejections. On the other hand, radiative-MHD codes like Bifrost initialised with analytical inputs have provided very...
The EVE Sun-as-a-star Doppler information has produced a surprising
result: hot active-region loops sustain steady flows on the order
of 100 km/s. The flows only occur at the higher temperatures (lines
of Mg XII and Fe XIV, for example), making the observation very
differential and redundant. Both of the EVE spectrographs (MEGS-A and
MEGS-B) show the effect. The flows are invariably in...
