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...
Coronal flare emission is commonly observed to decay on timescales longer than one-dimensional flare loop models typically predict. This discrepancy is most apparent during the gradual phase, where emission from impulsively driven models decays over minutes, in contrast to the hour or more often observed. Magnetic reconnection is invoked as the energy source of a flare, but should deposit...
Due to the magnetic connectivity between the flaring current sheet and magnetic footpoints, flare ribbon behavior must reflect current sheet processes at flare onset. In recent years, attention has turned to the role of the tearing mode instability in breaking down the current sheet at flare onset. The instability allows energy release to accelerate via the reconnection of progressively...
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...
For over a decade, the Bifrost code has established itself as a capable tool for simulating stellar atmospheres. Many scientific projects benefitted from Bifrost's detailed numerical models of the chromosphere and corona in the quiet Sun. Although it is a very optimized code, its time integration method, which uses global time stepping, makes it prohibitively expensive to run an experiment...
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...
Studies of the solar chromosphere are an important component of our understanding of heating and energy transfer in the solar atmosphere $-$ however, the predominance of non-equilibrium and non-LTE physics there complicates numerical simulation of this region. In contrast, the millimeter continuum serves as a "linear thermometer" of the chromosphere, allowing it to serve as a crucial...
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...
Solar eruptive phenomena are often associated with a variety of radio bursts observed from metric to kilometric wavelengths. Type II and type III bursts are both generated via the plasma emission mechanism, when beams of relativistic electrons interact with ambient plasma producing radio emissions at the local plasma frequency or its first harmonic. Here, we analyze a unique multi-spacecraft...
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...
Prominence oscillations are commonly known for their use in prominence seismology when the plasma and magnetic field properties are derived from the oscillatory properties such as periods, damping, and times. However, how the oscillations are induced in those dense and cold structures remains unclear. Observations from SDO/AIA, SMART showed the activations with the incoming waves, which could...
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 heating of the outer layers of the solar atmosphere is still far from being completely understood. In this sense, in the last few years we have witnessed a huge step forward in our understanding from both a theoretical and an observational perspective. This has been possible due to the inclusion of new physics in the former and the deployment of new observing facilities that has opened...
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...
Lower atmospheric lines show peculiar profiles at the leading edge of ribbons during flares. In particular, increased absorption of the BBSO/GST HeI 10830 A line (e.g. Xu2016), as well as broad and centrally reversed profiles in the MgII and CII spectra observed by the IRIS satellite (e.g. Panos2018) have been reported. In this work, we aim to understand the physical origin of the IRIS ribbon...
Solar jets are observed as collimated plasma beams over a large range of temperatures and wavelengths. They have been observed in H and optical lines for more than 50 years and called surges. The term "jet" comes from X-ray observations after the launch of the Yohkoh satellite in 1991. They are the means of transporting energy through the heliosphere and participate to the corona...
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...
