arXiv subjects

Mats Carlsson

Publications and source records attributed to Mats Carlsson.

At least 19 recordsLinked to original sources

arXiv2026

Investigating white-light flare mechanisms via the Paschen jump using high-resolution continuum observations from the Swedish 1-m Solar Telescope

The continuum is understood to contain a large portion of the energy emitted by a solar flare. The optical continuum, known as white light (WL), is particularly relevant since it may be observed by ground-based instruments. We measured the WL enhancements short- and longward of the Paschen jump in order to gain insights into the possible mechanism(s) behind the creation of these increases in our two case studies. We took measurements from the Swedish 1-m Solar Telescope of the pseudo-continuum around the Ca II 8542 {\AA} line as well as the true continuum around the K I 7699 {\AA} and the Fe I 6173 {\AA} line, providing us with observations on both sides of the Paschen jump. We observe WL enhancements of over 40% against the dark (pen-) umbral background in both flares. The WL excess in flare 1 is co-temporal with the derivative of the GOES soft X-ray and hard X-ray (HXR) measurements from the Advanced Space-based Solar Observatory (ASO-S), and the flare is compatible with the Neupert effect. For flare 2, a preceding smaller flare may be the cause of the temporal discrepancy. Signatures of chromospheric evaporation and condensation are found in the WL area for both flares. The ratio of intensities blueward and redward of the Paschen jump in flare 1 is below one for most WL pixels. This is in disagreement with the accepted WL formation mechanisms. We believe this is a consequence of the Ca II 8542 {\AA} pseudo-continuum being affected by line wing opacity changes. The co-temporality of WL and HXR enhancements suggests that the WL emission enhancements in flare 1 (and parts of flare 2) are a result of direct electron precipitation. We conclude that more reliable continuum measurements free of any nearby line influence are necessary in order to obtain conclusive evidence for the formation mechanism(s) behind optical continuum enhancements from such analysis as presented in this work.

astro-ph.SR↗

arXiv2026

Characterization of white-light enhancements under umbral conditions in one-dimensional simulations of solar flares

Solar flares with signatures in the optical continuum (white light, WL) pose a challenge to the standard flare model and to solar flare simulations. In particular, simulations are so far not able to convincingly reproduce observed WL enhancements. We investigate the effect of different electron beams on an umbral atmosphere and what the differences and similarities to the quiet-Sun response are. We characterized WL emission in one-dimensional simulations of solar flares using the radiation hydrodynamics code RADYN. We used a similar setup as the F-CHROMA grid, but with a starting atmosphere describing umbral conditions. We investigated the influence of different temporal profiles of an electron beam on this umbral atmosphere. Our simulations show maximum WL increases between 40 and 335%, which is comparable to observed values. The reduced umbral background is the main reason for these large increases. We identify hydrogen recombination in an optically thin chromosphere as the dominant process responsible for the increases, with the radiation from the heated photosphere becoming substantial in the later stages due to the longer timescale of the cooling of the photosphere compared to hydrogen recombination in the chromosphere. Shorter, more intense beams (i.e., beams with a higher maximum energy flux) lead to a faster and more dramatic atmospheric evolution. Such beams also cause larger WL enhancements due to a higher electron density in the relevant layers. Both the Balmer ratio and the Paschen ratio are substantially higher in our simulations compared to simulations with a quiet-Sun atmosphere. The detectability and amplitude of WL enhancements depends on the spectral and temporal structure of the electron beam as well as the underlying background radiation. The combination of a short, intense beam and an umbral atmosphere provides an excellent seed for substantial WL enhancements.

astro-ph.SR↗

arXiv2026

Chromospheric dynamics and the O I 135.6~nm spectral line

The O I 135.6 nm spectral line is formed in the chromosphere at the same heights as the Mg II h&k line cores are formed. As the O I line is optically thin, it represents a possibility for measuring the non-thermal velocities in this region without the complications added by optically thick radiative transfer. Numerical models have hitherto strained to reproduce Mg II core line widths, challenging current understanding of chromospheric energetics and dynamics. We aim to construct numerical models, varying physical and numerical parameters in order to asses which of these is most important in setting the Mg II core intensity and width. A set of numerical models of varying resolution, size, magnetic topology and strength are considered and used to synthesize O I line emission and to investigate the constraints that observations of this line place on chromospheric dynamics and densities. We find that, for quiet Sun, while non-thermal motions undeniably provide a source of Doppler broadening and chromospheric mass loading, the average strength of the photospheric magnetic field is the most important parameter in setting the Mg II core width to values within 5 km/s of observed values. Furthermore, for plage, we identify non-equilibrium hydrogen ionization and three dimensional radiative transfer as important ingredients in understanding chromospheric diagnostics and deciphering chromospheric structure.

astro-ph.SR↗

arXiv2026

Chromosphere of the quiet sun: II. Atmospheric response to small-scale magnetic flux emergence

Coupling between the photosphere, chromosphere and corona in the quiet Sun (QS) is governed by a complex interplay between magnetic structuring, heating, mass loading, and radiative cooling. Constraining how this balance responds to variations in small-scale magnetic flux remains limited. We investigate how chromospheric heating and its thermodynamic coupling to higher atmospheric layers vary as a function of small-scale magnetic flux emergence. We performed a parametric set of 3D radiative-MHD simulations with the Bifrost code, starting from a weakly magnetised QS reference model and injecting horizontal magnetic flux of increasing amplitude into the sub-surface convection zone. The resulting chromospheric dynamics, heating, mass loading, and coronal response were analysed. Chromospheric temperatures and mechanical heating rise monotonically with increasing magnetic-field strength. Although the fractional contribution of shocks decreases, reconnecting current sheets keeps maintaining about 50%. In contrast, the temperature at the base of the corona exhibits a non-monotonic response, reaching a maximum at intermediate magnetic amplitudes and decreasing for the strongest-field case. We show that stronger magnetic-field strength increases chromospheric heating, which increases the coronal-base density through efficient mass loading, and amplifies radiative losses. These density-driven radiative losses dominate the coronal energy balance and thus lead to reduced coronal-base temperatures despite increased heating. Our results demonstrate the sensitivity of chromospheric structure and dynamics to small-scale flux emergence, and its key role in regulating coronal thermodynamics. This result illustrates the chromosphere-s role as a thermodynamic gatekeeper, and further warrants future investigations of atmospheric models relevant to global solar-wind models and space-weather forecasts.

astro-ph.SR↗

arXiv2025

Shock-induced magnetic reconnection driving Ellerman bomb emission and a spicule

The mechanism that forms dynamic type II spicules has remained elusive for many years. Their dynamical behaviour has long been linked to magnetic reconnection, yet no conclusive evidence has been provided. However, one recent observational study found signs of reconnection, as traced by Ellerman bombs (EBs), at the footpoints of many spicules. The triggering of EBs is generally linked to reconnection due to flux emergence and convective motions in the photosphere. We aim to explore whether we can connect EBs to type II spicules, and to what extent we can use EBs as an observational proxy to probe reconnection in this dynamic. We also aim to provide further insight into the mechanisms that trigger EBs. We used a simulation run with the radiative magnetohydrodynamics code Bifrost to track spicules and study the physical processes behind their formation. To detect EBs and classify the spicules, we synthesised the H-alpha line using the multilevel radiative transfer code RH1.5D. We also traced shocks and current sheets to decipher the origin of EBs and spicules. We selected one type II spicule with a strong EB near its footpoint and studied their formation in detail. A magnetoacoustic shock advects the magnetic field lines towards an oppositely directed ambient field, creating a current sheet. The current sheet accelerates dense plasma via a whiplash effect generated by reconnection into the inclined ambient field, launching the spicule. Several EB profiles trace shock- and magnetic-reconnection-induced dynamics during this process at the spicule footpoint. We present a new EB triggering mechanism in which a shock-induced current sheet reconnects, triggering an EB in the lower solar atmosphere. The shock-induced current sheet generates the launch of a type II spicule via reconnection outflows. These results provide a physical origin for the observed connection between EBs and spicules.

astro-ph.SR↗

arXiv2025

Predicted white-light solar flare emission from the F-CHROMA grid of models

Much of a solar flare's energy is thought to be released in the continuum. The optical continuum (white light) is of special interest due to the ability to observe it from the ground. We aim to investigate the prevalence of white-light (WL) emissions in simulations of purely electron beam-driven solar flares, what determines the occurrence of these enhancements, and the underlying causes. We utilized the F-CHROMA grid of flare simulations created using the radiative hydrodynamics code RADYN. We probed the spectral index, total energy, and low-energy cutoff to draw conclusions about their relationships to the white-light intensity. Furthermore, we calculated the 6684 {\AA} continuum intensities, the Balmer, and the Paschen ratios. Finally, we analyzed two particular cases, one with high 6684 {\AA} intensity and one with a large Balmer ratio, to determine the dominant mechanisms in these simulations. 33 of the 84 flares included in the F-CHROMA grid show white-light intensity enhancements that exceed 0.1% relative to the pre-flare level. We conclude that, with the parameters presented in the F-CHROMA grid, purely electron beam-driven simulations of solar flares are not able to reproduce observed WL enhancements, as the maximum enhancements in the grid are below 4%. The total energy (which is correlated with the maximum beam flux) is the main factor for deciding whether excess white-light emissions will be detectable. There is a linear relationship between the Balmer (and Paschen) ratio and the relative continuum increase. Both case studies show that during the time of maximum WL excess, hydrogen ionization and subsequent recombination in an optically thin medium is the dominant mechanism for WL continuum emission enhancements. Increased H$^-$ emission in the photosphere as a result of radiative backwarming becomes dominant during the declining phase of WL emissions in both case studies.

astro-ph.SR↗

arXiv2025

Chromosphere of the quiet sun -- I. Shock and current-sheet dynamics and heating

The solar chromosphere is a crucial interface between the solar interior and its interplanetary environment, regulating how energy is locally deposited into heat and transported into the upper atmospheric layers. Despite significant progress, the dominant processes responsible for chromospheric heating remain debated, particularly under quiet-Sun (QS) conditions. We aim to disentangle and quantify the respective roles of shocks and current sheets (CS) in QS chromospheric modeling. We use a simulation performed with the radiation-magnetohydrodynamics code Bifrost. In order to identify shocks and CS events across space and time, we develop and apply physics-based criteria, allowing us to describe their dynamics and evaluate their contributions to both dissipative (viscous and ohmic) and mechanical (including compressive work) heating. Shocks are found to dominate the energy deposition in the lower chromosphere (up to $59\%$ of the mechanical heating), while CS become the primary contributor in the upper chromosphere, as both plasma $\beta$ and Mach number $Ma$ drop. Overall, $66\%$ of the mechanical chromospheric heating is powered by the combined action of shocks and CS. These results support a multi-process view of the chromospheric heating in the QS, dominated by shocks, CS, and non-steep gradient dynamics. In addition to viscous and ohmic dissipation, compressive heating can play a major role locally in the model, particularly in chromospheric shock structures, where it offsets non-reversibly cooling from expansion and radiation, and therefore constitutes a key heating contribution to consider in the energy budget. This study further highlights the need for next-generation observations to resolve the intermittent and small-scale nature of chromospheric dynamics, in order to bring new constraints on the coupling between the different layers of the solar atmosphere.

astro-ph.SR↗

arXiv2025

Avalanches in Magnetohydrodynamical simulations

Scale invariance is a hallmark of many natural systems, including solar flares, where energy release spans a vast range of scales. Recent computational advances, at the level of both algorithmics and hardware, have enabled high-resolution magnetohydrodynamical (MHD) simulations to span multiple scales, offering new insights into magnetic energy dissipation processes. Here, we study scale invariance of magnetic energy dissipation in two distinct MHD simulations. Current sheets are identified and analyzed over time. Results demonstrate that dissipative events exhibit scale invariance, with power-law distributions characterizing their energy dissipation and lifetimes. Remarkably, these distributions are consistent across the two simulations, despite differing numerical and physical setups, suggesting universality in the process of magnetic energy dissipation. Comparisons between the evolution of dissipation regions reveals distinct growth behaviors in high plasma-beta regions (convective zone) and low plasma-beta regions (atmosphere). The latter display spatiotemporal dynamics similar to those of avalanche models, suggesting self-organized criticality and a common universality class.

astro-ph.SR↗

arXiv2024

Constraining the inner boundaries of COCONUT through plasma \b{eta} and Alfv\'en speed

Space weather modelling has been gaining importance due to our increasing dependency on technology sensitive to space weather effects, such as satellite services, air traffic and power grids. Improving the reliability, accuracy and numerical performance of space weather modelling tools, including global coronal models, is essential to develop timely and accurate forecasts and to help partly mitigate the space weather threat. Global corona models, however, require accurate boundary conditions, for the formulations of which we have very limited observational data. Unsuitable boundary condition prescriptions may lead to inconsistent features in the solution flow field and spoil the code's accuracy and performance. In this paper, we develop an adjustment to the inner boundary condition of the COCONUT global corona model to better capture the dynamics over and around the regions of stronger magnetic fields by constraining the plasma \b{eta} and the Alfv\'en speed. Using data from solar observations and solar atmospheric modelling codes such as Bifrost, we find that the baseline homogeneous boundary condition formulations for pressure and density do not capture the plasma conditions physically accurately. We develop a method to adjust these prescribed pressure and density values by placing constraints on the plasma \b{eta} and the Alfv\'en speed that act as proxies. We demonstrate that we can remove inexplicable fast streams from the solution by constraining the maximum Alfv\'en speed and the minimum plasma \b{eta} on the boundary surface. We also show that the magnetic topology is not significantly affected by this treatment otherwise. The presented technique shows the potential to ease the modelling of solar maxima, especially removing inexplicable features while, at the same time, not significantly affecting the magnetic field topology around the affected regions.

physics.space-ph↗

arXiv2024

Time-dependent Stellar Flare Models of Deep Atmospheric Heating

Optical flares have been observed from magnetically active stars for many decades; unsurprisingly, the spectra and temporal evolution are complicated. For example, the shortcomings of optically thin, static slab models have long been recognized when confronted with the observations. A less incorrect -- but equally simple -- phenomenological $T \approx 9000$ K blackbody model has instead been widely adopted in the absence of realistic (i.e., observationally-tested) time-dependent, atmospheric models that are readily available. We use the RADYN code to calculate a grid of 1D radiative-hydrodynamic stellar flare models that are driven by short pulses of electron-beam heating. The flare heating rates in the low atmosphere vary over many orders of magnitude in the grid, and we show that the models with high-energy electron beams compare well to the global trends in flux ratios from impulsive-phase stellar flare, optical spectra. The models also match detailed spectral line shape properties. We find that the pressure broadening and optical depths account for the broad components of the hydrogen Balmer $γ$ lines in a powerful flare with echelle spectra. The self-consistent formation of the wings and nearby continuum level provide insight into how high-energy electron beam heating evolves from the impulsive to the gradual decay phase in white-light stellar flares. The grid is publicly available, and we discuss possible applications.

astro-ph.SR↗

arXiv2024

EMISSA: Exploring millimetre indicators of solar-stellar activity III. Comparison of Ca II indices and millimetre continua in a 3D model atmosphere

The Ca II H & K lines are strong chromospheric diagnostics that can be used to determine the temperature stratification and magnetic structure of the solar atmosphere. The Atacama Large Millimetre/Submillimetre Array (ALMA) offers complementary information on the thermal structure of stellar atmospheres using mm continuum radiation. The overall aim is to establish more robust solar/stellar activity indicators using ALMA observations in comparison with classical diagnostics, such as the s index and infrared triplet (IRT) index. A study was conducted using 1.5D radiative transfer codes RH1.5D and advanced radiative transfer (ART), along with an enhanced network atmosphere model generated by the state-of-the-art 3D radiation magnetohydrodynamics (rMHD) Bifrost code, to compute synthetic spectra for both Ca II lines and mm continua. To account for the limited spatial resolution of ALMA, we simulated the effect using a Gaussian point spread function (PSF). Additionally, we analysed the correlations and slopes of scatter plots between the Ca II indices and mm continuum for the original and degraded resolutions, focusing on the entire simulation box, quiet Sun regions, and enhanced network patches separately. The activity indices generated from these lines could further be used to compare the spectra of Sun-like stars with the solar spectrum. The Ca II activity indices and mm brightness temperatures are weakly correlated at the high resolution, with the highest correlation observed at a wavelength of 0.3 mm, corresponding to ALMA band 10. As the resolution decreases, the correlation consistently increases. Conversely, the slopes exhibit a decreasing trend with increasing wavelength, while the degradation of resolution does not noticeably affect the calculated slopes. Consequently, these relationships could be valuable for calibrating the mm continuum maps obtained through ALMA observations.

astro-ph.SR↗

arXiv2024

A comparative study of resistivity models for simulations of magnetic reconnection in the solar atmosphere. II. Plasmoid formation

Plasmoid-mediated reconnection plays a fundamental role in different solar atmospheric phenomena. Numerical reproduction of this process is therefore essential for developing robust solar models. Our goal is to assess plasmoid-mediated reconnection across various numerical resistivity models in order to investigate how plasmoid numbers and reconnection rates depend on the Lundquist number. We used the Bifrost code to drive magnetic reconnection in a 2D coronal fan-spine topology, carrying out a parametric study of several experiments with different numerical resolution and resistivity models. We employed three anomalous resistivity models: (1) the original hyper-diffusion from Bifrost, (2) a resistivity proportional to current density, and (3) a resistivity quadratically proportional to electron drift velocity. For comparisons, experiments with uniform resistivity were also run. Plasmoid-mediated reconnection is obtained in most of the experiments. With uniform resistivity, increasing the resolution reveals higher plasmoid frequency with weaker scaling to the Lundquist number, obtaining 7.9-12 plasmoids per minute for $S_L\in[1.8 \times 10^4, 2.6\times 10^5]$ with a scaling of $S_L^{0.210}$ in the highest-resolution resistivity cases, transcending into Petschek reconnection in the high-$S_L$ limit and Sweet-Parker reconnection in the low-$S_L$ limit. Anomalous resistivity leads to similar results even with lower resolution. The drift-velocity-dependent resistivity excellently reproduces Petschek reconnection for any Lundquist number, and similar results are seen with resistivity proportional to current-density. Among the different resistivity models applied on the given numerical resolution, the hyper-diffusion model reproduced plasmoid characteristics in closest resemblance to those obtained with uniform resistivity at a significantly higher resolution.

astro-ph.SR↗

arXiv2023

Comparative clustering analysis of Ca II 854.2 nm spectral profiles from simulations and observations

We aim to compare and contrast the typical shapes of synthetic Ca II 854.2 nm spectra found in Bifrost simulations having different magnetic activity with the spectral shapes found in a quiet Sun observation from the Swedish 1-m Solar Telescope (SST). We use clustering techniques to extract the typical Ca II 854.2 nm profile shapes synthesized from Bifrost simulations with varying amounts of magnetic activity. We degrade the synthetic profiles to observational conditions and repeat the clustering, and we compare our synthetic results with actual observations. While the mean spectra for our high resolution simulations compare reasonably well with the observations, we find that there are considerable differences between the clusters of observed and synthetic intensity profiles, even after the synthetic profiles have been degraded. The typical absorption profiles from the simulations are both narrower and display a steeper transition from the inner wings to the line core. Furthermore, even in our most quiescent simulation we find a far larger fraction of profiles with local emission around the core, or other exotic profile shapes, than in the observations. Looking into the atmospheric structure for a selected set of synthetic clusters, we find distinct differences in the temperature stratification for the clusters most and least similar to the observations. The narrow and steep profiles are associated with either weak gradients in temperature, or temperatures rising to a local maximum in the line wing forming region before sinking to a minimum in the line core forming region. The profiles that display less steep transitions show extended temperature gradients that are steeper in the range $-3 \lesssim \log τ_{5000} \lesssim -1$.

astro-ph.SR↗

arXiv2023

An optically thin view of the solar chromosphere from observations of the O I 1355Å spectral line

The O I 1355Å spectral line is one of the only optically thin lines that are both routinely observed and thought to be formed in the chromosphere. We present analysis of a variety of observations of this line with the Interface Region Imaging Spectrograph (IRIS), and compare it with other IRIS diagnostics as well as diagnostics of the photospheric magnetic field. We utilize special deep exposure modes on IRIS and provide an overview of the statistical properties of this spectral line for several different regions on the Sun. We analyze the spatio-temporal variations of the line intensity, and find that it is often significantly enhanced when and where magnetic flux of opposite polarities cancel. Significant emission occurs in association with chromospheric spicules. Because of the optically thin nature of the O I line, the non-thermal broadening can provide insight into unresolved small-scale motions. We find that the non-thermal broadening is modest, with typical values of 5-10 km/s, and shows some center-to-limb variation, with a modest increase towards the limb. The dependence with height of the intensity and line broadening off-limb is compatible with the line broadening being dominated by the superposition of Alfvén waves on different structures. The non-thermal broadening shows a modest but significant enhancement above locations that are in between photospheric magnetic flux concentrations in plage, i.e., where the magnetic field is likely to be more inclined with respect to the line-of-sight. Our measurements provide strict constraints on future theoretical models of the chromosphere.

astro-ph.SR↗

arXiv2023

A comparative study of resistivity models for simulations of magnetic reconnection in the solar atmosphere

Magnetic reconnection is a fundamental mechanism in astrophysics. A common challenge in mimicking this process numerically in particular for the Sun is that the solar electrical resistivity is small compared to the diffusive effects caused by the discrete nature of codes. We aim to study different anomalous resistivity models and their respective effects on simulations related to magnetic reconnection in the Sun. We used the Bifrost code to perform a 2D numerical reconnection experiment in the corona that is driven by converging opposite polarities at the solar surface. This experiment was run with three different commonly used resistivity models: 1) the hyper-diffusion model originally implemented in Bifrost, 2) a resistivity proportional to the current density, and 3) a resistivity proportional to the square of the electron drift velocity. The study was complemented with a 1D experiment of a Harris current sheet with the same resistivity models. The 2D experiment shows that the three resistivity models are capable of producing results in satisfactory agreement with each other in terms of the current sheet length, inflow velocity, and Poynting influx. Even though Petschek-like reconnection occurred with the current density-proportional resistivity while the other two cases mainly followed plasmoid-mediated reconnection, the large-scale evolution of thermodynamical quantities such as temperature and density are quite similar between the three cases. For the 1D experiment, some recalibration of the diffusion parameters is needed to obtain comparable results. Specifically the hyper-diffusion and the drift velocity-dependent resistivity model needed only minor adjustments, while the current density-proportional model needed a rescaling of several orders of magnitude.

astro-ph.SR↗

arXiv2023

Comparing Optimization Methods for Radiation Therapy Patient Scheduling using Different Objectives

Radiation therapy (RT) is a medical treatment to kill cancer cells or shrink tumors. To manually schedule patients for RT is a time-consuming and challenging task. By the use of optimization, patient schedules for RT can be created automatically. This paper presents a study of different optimization methods for modeling and solving the RT patient scheduling problem, which can be used as decision support when implementing an automatic scheduling algorithm in practice. We introduce an Integer Programming (IP) model, a column generation IP model (CG-IP), and a Constraint Programming model. Patients are scheduled on multiple machine types considering their priority for treatment, session duration and allowed machines. Expected future patient arrivals are included in the models as placeholder patients. Since different cancer centers can have different scheduling objectives, the models are compared using multiple objective functions, including minimizing waiting times, and maximizing the fulfillment of patients' preferences for treatment times. The test data is generated from historical data from Iridium Netwerk, Belgium's largest cancer center with 10 linear accelerators. The results demonstrate that the CG-IP model can solve all the different problem instances to a mean optimality gap of less than 1% within one hour. The proposed methodology provides a tool for automated scheduling of RT treatments and can be generally applied to RT centers.

math.OC↗

arXiv2023

Slow Solar Wind Connection Science during Solar Orbiter's First Close Perihelion Passage

The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilise the extensive suite of remote sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote sensing and in situ measurements of slow wind originating at open-closed field boundaries. The SOOP ran just prior to Solar Orbiter's first close perihelion passage during two remote sensing windows (RSW1 and RSW2) between 2022 March 3-6 and 2022 March 17-22, while Solar Orbiter was at a heliocentric distance of 0.55-0.51 and 0.38-0.34 au from the Sun, respectively. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low latency in situ data, and full-disk remote sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Post-observation analysis using the magnetic connectivity tool along with in situ measurements from MAG and SWA/PAS, show that slow solar wind, with velocities between 210 and 600 km/s, arrived at the spacecraft originating from two out of the three of the target regions. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter.

astro-ph.SR↗

arXiv2023

The F-CHROMA grid of 1D RADYN flare models

Context: Solar flares are the result of the sudden release of magnetic energy in the corona. Much of this energy goes into accelerating charged particles to high velocity. These particles travel along the magnetic field and the energy is dissipated when the density gets high enough, primarily in the solar chromosphere. Modelling this region is difficult because the radiation energy balance is dominated by strong, optically thick spectral lines. Aims: Our aim is to provide the community with realistic simulations of a flaring loop with an emphasis on the detailed treatment of the chromospheric energy balance. This will enable a detailed comparison of existing and upcoming observations with synthetic observables from the simulations, thereby elucidating the complex interactions in a flaring chromosphere. Methods: We used the 1D radiation hydrodynamics code RADYN to perform simulations of the effect of a beam of electrons injected at the apex of a solar coronal loop. A grid of models was produced, varying the total energy input, the steepness, and low-energy cutoff of the beam energy spectrum. Results: The full simulation results for a grid of models are made available online. Some general properties of the simulations are discussed.

astro-ph.SR↗