Realism of models has two components: sophistication of implemented physics and realism of the overall setup. Current 3D radiation MHD simulations of the coupled solar atmosphere are presenting a compromise on a middle ground. Domains are at best large enough to capture the extent of small active regions, but the commonly adapted use of periodic boundary conditions leads in many setups to an...
Task-based computing is offering a break-through in our capabilities to model astrophysical phenomena, and in particular in the context of solar modeling there are several routes along which we can take advantage of this general methodology. In the context of global modeling of the solar interior, we can utilize the ability to tune resolution as a function of depth, and by engaging very low...
Instrumentation for solar observations always represents a trade-off between spatial resolution, spectral resolution, field-of-view, time-coherence, calibration, and available money. The current state-of-the art for optical and near-infrared wavelengths consists of Fabry-Perot interferometers, and various types of imaging spectrographs.
In this talk I will discuss some aspects of these...
In this talk I will provide a brief overview of the upcoming solar missions focused on the Sun's corona: MUSE and Solar-C/EUVST, scheduled for launch in 2027 and 2028, respectively. The Multi-slit Solar Explorer (MUSE) is a NASA MIDEX mission, composed of a multi-slit EUV spectrograph (in three spectral bands around 171Å, 284Å, and 108Å) and an EUV context imager (in two passbands around 195Å...
Solar magnetic fields are essential ingredients for the energetics and dynamics of the lower solar atmosphere. After emergence, they continually interact with convective flows and with each other. The resulting field line braiding is believed to trigger magnetic reconnection in the chromosphere and above, generating a wide variety of features and contributing to atmospheric heating, both...
In this talk I will look at the scales at which photospheric motions generate waves and changes in the magnetic field topology. I will then discuss how these scales change throughout the solar atmosphere.
Recent observational studies on abundances reveal the need to expand models by considering different fluids and/or species to be constrained with these observations and interpret them. Similarly, radiative MHD models fail to reproduce observations of the coldest parts of the chromosphere and some properties of the Mg II profiles. Mg II is formed where interactions between multiple ionized and...
Solar chromosphere has been at the focus of solar physics studies for decades, but its heating mechanisms are still unknown. Chromospheric plasma is strongly stratified, weakly ionized and not completely collision coupled. In this talk I will overview our recent results of the modeling of solar chromosphere, comparing a more standard single-fluid approach and a more novel multi-fluid approach....
Recent observations performed by space missions (SDO, Hinode) prove the existence of mini-filament eruptions within the solar chromosphere that could be connected to the formation of chromospheric jets and spicules. The growth of the helical kink instability within these structures is responsible of the onset of magnetic reconnection and lead to explosive events occurring ubiquitously in the...
The chromospheric heating terms cannot be inferred directly from observational datasets. Furthermore, even estimating the thermodynamical state of the plasma usually involves complex NLTE inversion calculations. Therefore, it has been very difficult to quantify in which proportion different heating mechanisms could be operating at different locations of the chromosphere.
One of the most...
The MURaM radiation-magnetohydrodynamics code has long been applied to simulate near-surface magnetoconvection, ranging from quiet sun conditions to complex active regions. The code includes the physics required to treat the convection zone, and the solar atmosphere from the photosphere to the corona. Until now, these simulations have been limited to a local-thermodynamic equilibrium treatment...
This study presents a comparison of the high frequency wave power found in
3D numerical MHD models of the solar atmosphere (Bifrost and MURaM)
with real observations of chromospheric lines. We
also discuss the systematics originating from using different
models to calculate the acoustic wave flux in the solar chromosphere.
In particular, we synthesize from the MHD models spectral lines...
The chromosphere is a very dynamic part of the solar atmosphere. With short time scales and small spatial scales at which fundamental physical processes are taking place, it is a challenge to get a clear observational view of the chromosphere. The CRISP and CHROMIS tunable filter instruments at the Swedish 1-m Solar Telescope (SST) on La Palma are capable of fast wavelength sampling while...
Recent magnetohydrodynamic models show that many of the chromospheric features and their dynamics can be reproduced to some degree. The models demonstrate that the overall appearance of synthetic chromosphere depends mostly on the field configuration and the treatment of the small-scale dynamics. In this talk, the properties of these models are presented, as well as their comparison to...
Nowadays, solar spectra are routinely analyzed to understand the physical mechanisms that trigger different physical phenomena. These spectral lines are modeled using approaches of increasing complexity, ranging from a simple Gaussian model to complex non-LTE radiative transfer calculations. In practice, these data are also affected by telescope degradation, may include some instrumental...
Recent observations revealed loop-like structures at very small scales visible in observables that sample transition region (TR) and coronal temperatures. Their formation remains unclear.
We study an example of a bipolar system in realistic magnetohydrodynamic simulations and forward synthesis of spectral lines to investigate how these features occur.
Computations are done using the...
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...
The solar coronal mass ejection (CME) is a global phenomenon that not only disrupts the solar atmosphere but also leads to hazardous space weather events when propagating through the heliosphere. The forecast capability of the CME impacts depends critically on our understanding about the plasma environment of the CME source region, and the physical processes involved when CME interacts with...
The source regions of the solar wind, and their drivers and acceleration mechanisms, remain key topics of study in heliophysics with many open questions. One of the major challenges is to connect heliospheric measurements of the solar wind and solar energetic particles with possible source regions in the solar atmosphere, such as active region outflows and coronal holes, and there are now...
Magnetic Flux Ropes (MFRs) are free-energy-carrying, three-dimensional magnetized plasma structures characterized by twisted magnetic field lines and are widely considered the core structure of Coronal Mass Ejections (CMEs) propagating in the interplanetary space. The way MFRs form remains unclear as different theories predict that either MFRs form during the initiation of the CME or pre-exist...
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...
Understanding the solar atmosphere, which connects to the heliosphere via radiation, the solar wind and coronal mass ejections, and energetic particles is pivotal for establishing the conditions for life and habitability in the solar system. SOLAR-C (EUVST) (EUV High-Throughput Spectroscopic Telescope) is designed to comprehensively understand the energy and mass transfer from the solar...
The 3D extensions to the Standard model of solar flares have been succcessfull in explaining various observed phenomena. Among them, there are (1) hot cores (sigmoids), (2) apparent slipping motion of flare looops, (3) saddle-shaped flare arcades, as well as (4) reconnection of the drifting flux rope with the surrounding corona or itself during the eruption. We review the properties of the 3D...
To understand the trigger of solar flares and eruptions it is necessary to obtain an accurate description of the 3D pre-eruptive coronal magnetic configuration. The latter is not directly observable and one must rely either on static modelling/extrapolation from 2D photospheric measurements, and/or on relatively idealized time-evolution of a magnetic model from numerical simulations. The...
Solar flares are transient yet dramatic events in the atmospheres of the Sun, during which vast amounts of magnetic energy is liberated. This energy is subsequently transported through the solar atmosphere or into the heliosphere, and together with coronal mass ejections flares comprise a fundamental component of space weather. Thus, understanding the physical processes at play in flares is...
Solar flares are amongst the most energetic events in our solar system. Accompanied by intense UV and X-ray emissions, energetic particles and coronal mass ejections can be injected into the interplanetary medium during flares. As these various aspects can have a large impact on solar system bodies and a detrimental effect on human activities, there is a strong interest to gain a deeper...
Solar coronal jets are observed as collimated plasma flows with high velocity along magnetic field lines in a wide wavelength range, from X-rays to EUV. Occasionally these hot jets are closely related to cool surges, which are chromospheric ejections that emerge in the form of unwrinkled threads. Though these phenomena have been studied over the past few decades with different instruments and...
The overall paradigm of flare energy release is well-known. An energy-bearing coronal magnetic field relaxes via magnetic reconnection to a lower energy state, and the energy released is converted and dissipated in the radiation flash that is a solar flare. But what does that energy conversion and energy dissipation involve? There are strong and long-standing pointers to an important role for...
Magnetic reconnection governing energy release in solar flares takes place in the corona; the lower atmosphere responds rapidly to energy transfer from the corona, generating prominent radiation and dynamic signatures that help us infer properties of energy release and transfer. Fine-scale structures embedded in the generally curvilinear-shaped flare ribbons indicate the global organization of...
According to our current understanding, solar flares are driven by magnetic energy stored in the solar corona being rapidly released through a process involving magnetic reconnection. This scenario was originally proposed on the basis of classic observations including radio and hard X-ray emission from non-thermal electrons accompanying rising emission from hot thermal plasma. Over the past...
Coronal mass ejections (CMEs) are the largest scale eruptions of plasmas in the solar corona. Many observations show that pre-eruptive CMEs always appear as bright structures in EUV high-temperature bands and rise slowly when approaching the onset of their eruption. However, the mechanisms behind these phenomena are still puzzling. In this work, we aim to explore these by combining...
Solar active regions are thought to be formed by the emergence of magnetic flux from the deep convection zone and, therefore, it is important to use a large computational domain covering the entire convection zone to understand the physics behind. However, the high acoustic speed makes it difficult to conduct magnetohydrodynamic simulations in such a deep domain. The R2D2 code overcomes this...
Light bridges, as seen in photospheric layers, are irregular, bright, and elongated structures that cross the umbra during the formation and decay of sunspots or pores. They play an important role in our understanding of the evolutionary stages of sunspots as they can indicate the break-up of sunspots in the decay or the formation phases of complex active regions. These structures have been...
Quasi-simultaneous Ellerman bombs and UV bursts have been shown to result from the reconnection of emerging flux with itself when part of the emerging field remains in photospheric heights while the flanks of the retained field rise to chromospheric and coronal heights (Hansteen et al A&A 626, A33, 2019; Ortiz et al A&A 633, A58, 2020). This conclusion was reached using 3D Bifrost numerical...
The Atacama Large Millimeter/submillimeter Array (ALMA) offers new diagnostic capabilities that complement other commonly used diagnostics for exploring our Sun. In particular, ALMA's abilities as an essentially linear thermometer of the chromospheric gas at unprecedented spatial resolution at mm wavelengths and future polarization measurements have great scientific potential. In concert...
Solar flares evolve on multiple scales and cannot be explained or simulated without considering the effects of accelerated particles. The particles reach non--thermal velocities due to the release of magnetic energy through magnetic reconnection, and they are observed through hard X-ray emission and ultraviolet radiation produced in flare ribbons. However, the key processes behind the...
The Sun, being the nearest star, can be used as a reference case for solar-like stars due to the availability of many spatiotemporally resolved solar spectra. Amongst several spectral lines, some of the strongest chromospheric diagnostics are the Ca II H & K lines which can be used to gauge the temperature stratification of the atmosphere as the line core and wings are formed in different...
Solar prominences consist of cool and dense plasma that is suspended in the corona, surrounded by hotter and less dense coronal material. As predecessors of coronal mass ejections, solar prominences are important drivers of space weather, but their exact formation mechanism is still unknown. We use the radiative magnetohydrodynamic code MURaM to simulate the formation and dynamics of...
Prominences are large-scale structures found in the solar corona, characterized by two orders of magnitude larger densities and lower temperatures than their surroundings. On a large scale they are relatively stable structures, closer-up they exhibit intricate and complex dynamics with small-scale structures [1]. Prominences form via thermal instability, an in-situ condensation process that is...
The OI 135.56 nm line and CI 135.58 nm line are weak lines that are covered by NASA's Interface Region Imaging Spectrograph (IRIS) mission which studies how the solar atmosphere is energized. The emission in the OI 135.56 nm line is dominated by a recombination cascade. This line provides powerful diagnostics of unresolved velocity fields in the chromosphere. In this work, we study the...
The Lyman Continuum (LyC; <912Å) forms at the top of the chromosphere, making it a powerful tool for probing the chromospheric plasma during solar flares. SDO/EVE has observed many LyC disk-integrated flares, though this is a largely untapped dataset (aside from Machado et al 2018). Further, SolO/SPICE also provides partial coverage of the LyC (704-790Å), whilst the upcoming Solar-C/EUVST will...
In this contribution I present our first results from global MHD simulations of the Solar convective region using DISPATCH framework. The simulation spans 0.655 - 0.995 of the solar radius, over the entire surface using Cartesian patches, arranged in a Volleyball decomposition.
I present the current status and future outlook.
In this study, we investigate motions in the hot plasma in the above-the-loop-top (ALT) region during the 2017 September 10 X8.2 flare event. We examine the region to the south of the main flare arcade, where there is data from the Interface Region Imaging Spectrograph (IRIS) and the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. We find that there are initial blueshifts of 20–60...
Current models of the solar atmosphere involve a comprehensive set of physics including the treatment of magnetic fields, heat conduction and radiative transfer (RT). Forward models that simulate the different layers of the solar atmosphere self consistently open the door to study the most complicated layers of the atmosphere that are subject to non local thermal equilibrium (NLTE) and non...
Confronting numerical simulations with observational studies
is necessarily based on an underlying theoretical description, which describes the dominant physical processes that are being numerically simulated and observationally analyzed. We consider several generalizations of the well-known fluid model of Braginskii (1965). We use the Landau collisional operator and the moment method of...
Detection of dynamic fibrils (DFs) in coronal images had been a difficult task so far, primarily due to their small size and the lower spatial resolution of the current EUV imagers. In this talk, I will present the first unambiguous detection of DFs in coronal EUV data using high-resolution images from the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter. Using the EUI 174 Å data, we...
Multiwavelength co-temporal observations of solar prominences are still rare, even if many space and ground-based observatories and techniques are available. In April 19, 2018 a quiescent prominence with fine structures was observed with IRIS, ALMA (band 3) and in H$\alpha$ line with Wroclaw MSDP (Multichannel Subtractive Double Pass) spectrograph. Both UV and H$\alpha$ data contains spectra...
Short-lived (100s or less), sub-arcsec to a couple of arcsec sized features of enhanced brightenings in the narrowband images at the $\mathrm{H_{2V}}$ and $\mathrm{K_{2V}}$ positions of the Ca II H&K lines in the quiet Sun are known as bright grains. These bright grains are interpreted as manifestations of acoustic shock waves in the chromosphere. Using simulations, earlier studies have shown...
Magnetic reconnection in the deep solar atmosphere can give rise to enhanced emission in the Balmer hydrogen lines, a phenomenon referred to as Ellerman bombs. Recent high quality Hβ observations indicate that Ellerman bombs are more common than previously thought and it was estimated that at any time about half a million Ellerman bombs are present in the quiet Sun. We performed an extensive...
The internal dynamics of solar prominences have been observed to be highly complex for many decades, many of which also indicate the possibility of turbulence. Prominences represent large-scale, dense condensations suspended against gravity at great heights within the solar atmosphere. Therefore, it is no surprise that the fundamental process of the Rayleigh-Taylor (RT) instability has been...
The solar corona is continuously studied through observations and numerical modelling due to its extreme temperatures. One of the prime candidates in understanding these temperatures is nanoflares, which are small-scale events associated with magnetic reconnection in the solar atmosphere. Observations of small-scale events with nanoflare energies are rare because signatures from non-thermal...
Spicules are one of the most intriguing phenomena of the lower solar atmosphere. In spite of decades of research, they remain mysterious. From our initial work on how solar p-modes may generate spicules (Nat. 2004), through showing the formation of a forest of them using radial MHD simulations (Nat. Phys. 2022), finally we are able to report a more unified theory of spicular physics,...
With the imminent exascale era, many legacy codes face a variety of challenges to become portable to GPU machines, like LUMI. We would like to give an overview on the status of Bifrost physics capabilities supported on GPUs and possible applications. We will share our experiences so far in exploring portability with directives approaches while using different compilers and architectures.
The present work investigates solar coronal dynamics, in particular streamer waves. Recent observations combined with advanced numerical tools allow to gain insight into the nature of the coronal streamers and their oscillations. The numerical model for the streamer waves was constructed with the MPI-AMRVAC code in the framework of 2.5D ideal magnetohydrodynamics. We performed a parameter...
Solar flares are known to accelerate electrons to high energies efficiently. However, how the underlying acceleration mechanisms work remains poorly understood. The angular distribution of the accelerated electrons, the resultant hard X-ray emission, and its polarization and directional anisotropy are key to solving this mystery. The solar PolArization and Directivity X-Ray Experiment (PADRE)...
Solar flares release magnetic energy in reconnection events heating the atmosphere in the process. Solar flares are inherently multi-scale; The entire flare may stretch Mm scales and evolve on timescales of hours, while the reconnection region is far smaller, on the order of particle mean free path, and may have timescales of just a few seconds. The small scales break the fluid description...
