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M Carlsson - One of the best experts on this subject based on the ideXlab platform.
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on the origin of the magnetic energy in the quiet solar Chromosphere
The Astrophysical Journal, 2019Co-Authors: Juan Martinezsykora, Bart De Pontieu, V H Hansteen, M Carlsson, Boris Vilhelm Gudiksen, Milan GosicAbstract:The presence of magnetic field is crucial in the transport of energy through the solar atmosphere. Recent ground-based and space-borne observations of the quiet Sun have revealed that magnetic field accumulates at photospheric heights, via a local dynamo or from small-scale flux emergence events. However, most of this small-scale magnetic field may not expand into the Chromosphere due to the entropy drop with height at the photosphere. Here we present a study that uses a high resolution 3D radiative MHD simulation of the solar atmosphere with non-grey and non-LTE radiative transfer and thermal conduction along the magnetic field to reveal that: 1) the net magnetic flux from the simulated quiet photosphere is not sufficient to maintain a chromospheric magnetic field (on average), 2) processes in the lower Chromosphere, in the region dominated by magneto-acoustic shocks, are able to convert kinetic energy into magnetic energy, 3) the magnetic energy in the Chromosphere increases linearly in time until the r.m.s. of the magnetic field strength saturates at roughly 4 to 30 G (horizontal average) due to conversion from kinetic energy, 4) and that the magnetic features formed in the Chromosphere are localized to this region.
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two dimensional radiative magnetohydrodynamic simulations of partial ionization in the Chromosphere ii dynamics and energetics of the low solar atmosphere
The Astrophysical Journal, 2017Co-Authors: Juan Martinezsykora, Bart De Pontieu, V H Hansteen, M Carlsson, Daniel Nobregasiverio, Boris Vilhelm GudiksenAbstract:We investigate the effects of interactions between ions and neutrals on the Chromosphere and overlying corona using 2.5D radiative MHD simulations with the Bifrost code. We have extended the code capabilities implementing ion-neutral interaction effects using the Generalized Ohm's Law, i.e., we include the Hall term and the ambipolar diffusion (Pedersen dissipation) in the induction equation. Our models span from the upper convection zone to the corona, with the photosphere, Chromosphere and transition region partially ionized. Our simulations reveal that the interactions between ionized particles and neutral particles have important consequences for the magneto-thermodynamics of these modeled layers: 1) ambipolar diffusion increases the temperature in the Chromosphere; 2) sporadically the horizontal magnetic field in the photosphere is diffused into the Chromosphere due to the large ambipolar diffusion; 3) ambipolar diffusion concentrates electrical currents leading to more violent jets and reconnection processes, resulting in 3a) the formation of longer and faster spicules, 3b) heating of plasma during the spicule evolution, and 3c) decoupling of the plasma and magnetic field in spicules. Our results indicate that ambipolar diffusion is a critical ingredient for understanding the magneto-thermo-dynamic properties in the Chromosphere and transition region. The numerical simulations have been made publicly available, similar to previous Bifrost simulations. This will allow the community to study realistic numerical simulations with a wider range of magnetic field configurations and physics modules than previously possible.
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heating of the magnetic Chromosphere observational constraints from ca ii λ8542 spectra
The Astrophysical Journal, 2013Co-Authors: J De La Cruz Rodriguez, M Carlsson, B De Pontieu, Rouppe L Van Der VoortAbstract:The heating of the Sun’s Chromosphere remains poorly understood. While progress has been made on understanding what drives the quiet Sun internetwork Chromosphere, chromospheric heating in strong magnetic field regions continues to present a difficultchallenge, mostly because of a lack of observational constraints. We use high-resolution spectropolarimetric data from the Swedish 1-m Solar Telescope to identify the location and spatio-temporal properties of heating in the magnetic Chromosphere. In particular, we report the existence of raised-core spectral line profiles in the Ca II �8542 line. These profiles are characterized by the absence of an absorption line core, showing a quasi-flat profile between � � ±0.5 A, and are abundant close to magnetic bright-points and plage. Comparison with 3D MHD simulations indicates that such profiles occur when the line-of-sight goes through an "elevated temperature canopy" associated with the expansion with height of the magnetic field of flux concentrations. This temperature canopy in the simulations is caused by ohmic dissipation where there are strong magnetic field gradients. The raised-core profiles are thus indicators of locations of increased chromospheric heating. We characterize the location and temporal and spatial properties of such profiles in our observations, thus providing much stricter constraints on theoretical models of chromospheric heating mechanisms than before. Subject headings: Sun: Chromosphere — Sun: magnetic topology — Sun: faculae, plages — line: formation — magnetohydrodynamics — polarization
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on the minimum temperature of the quiet solar Chromosphere
Astronomy and Astrophysics, 2011Co-Authors: J Leenaarts, V H Hansteen, M Carlsson, Boris Vilhelm GudiksenAbstract:Aims. We aim to provide an estimate of the minimum temperature of the quiet solar Chromosphere. Methods. We perform a 2D radiation-MHD simulation spanning the upper convection zone to the lower corona. The simulation includes non-LTE radiative transfer and an equation-of-state that includes non-equilibrium ionization of hydrogen and non-equilibrium H2 molecule formation. We analyze the reliability of the various assumptions made in our model in order to assess the realism of the simulation. Results. Our simulation contains pockets of cool gas with down to 1660 K from 1 Mm up to 3.2 Mm height. It overestimates the radiative heating, and contains non-physical heating below 1660 K. Therefore we conclude that cool pockets in the quiet solar Chromosphere might have even lower temperatures than in the simulation, provided that there exist areas in the Chromosphere without significant magnetic heating. We suggest off-limb molecular spectroscopy to look for such cool pockets and 3D simulations including a local dynamo and a magnetic carpet to investigate Joule heating in the quiet Chromosphere.
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on the solar Chromosphere observed at the limb with hinode
The Astrophysical Journal, 2010Co-Authors: P G Judge, M CarlssonAbstract:Broadband images in the Ca II H line, from the Broadband Filter Imager (BFI) instrument on the Hinode spacecraft, show emission from spicules emerging from and visible right down to the observed limb. Surprisingly, little absorption of spicule light is seen along their lengths. We present formal solutions to the transfer equation for given (ad hoc) source functions, including a stratified Chromosphere from which spicules emanate. The model parameters are broadly compatible with earlier studies of spicules. The visibility of Ca II spicules down to the limb in Hinode data seems to require that spicule emission be Doppler shifted relative to the stratified atmosphere, either by supersonic turbulent or organized spicular motion. The non-spicule component of the Chromosphere is almost invisible in the broadband BFI data, but we predict that it will be clearly visible in high spectral resolution data. Broadband Ca II H limb images give the false impression that the Chromosphere is dominated by spicules. Our analysis serves as a reminder that the absence of a signature can be as significant as its presence.
Alex Russell - One of the best experts on this subject based on the ideXlab platform.
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simulations of the mg ii k and ca ii 8542 lines from an alfven wave heated flare Chromosphere
The Astrophysical Journal, 2016Co-Authors: Graham S Kerr, Alex Russell, L Fletcher, Joel C AllredAbstract:We use radiation hydrodynamic simulations to examine two models of solar flare chromospheric heating: Alfven wave dissipation and electron beam collisional losses. Both mechanisms are capable of strong chromospheric heating, and we show that the distinctive atmospheric evolution in the mid-to-upper Chromosphere results in Mg ii k-line emission that should be observably different between wave-heated and beam-heated simulations. We also present Ca ii 8542 A profiles that are formed slightly deeper in the Chromosphere. The Mg ii k-line profiles from our wave-heated simulation are quite different from those from a beam-heated model and are more consistent with Interface Region Imaging Spectrograph observations. The predicted differences between the Ca ii 8542 A in the two models are small. We conclude that careful observational and theoretical study of lines formed in the mid-to-upper Chromosphere holds genuine promise for distinguishing between competing models for chromospheric heating in flares.
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alfvenic wave heating of the upper Chromosphere in flares
The Astrophysical Journal, 2016Co-Authors: Jeffrey W Reep, Alex RussellAbstract:We have developed a numerical model of flare heating due to the dissipation of Alfv\'enic waves propagating from the corona to the Chromosphere. With this model, we present an investigation of the key parameters of these waves on the energy transport, heating, and subsequent dynamics. For sufficiently high frequencies and perpendicular wave numbers, the waves dissipate significantly in the upper Chromosphere, strongly heating it to flare temperatures. This heating can then drive strong chromospheric evaporation, bringing hot and dense plasma to the corona. We therefore find three important conclusions: (1) Alfv\'enic waves, propagating from the corona to the Chromosphere, are capable of heating the upper Chromosphere and the corona, (2) the atmospheric response to heating due to the dissipation of Alfv\'enic waves can be strikingly similar to heating by an electron beam, and (3) this heating can produce explosive evaporation.
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propagation of alfvenic waves from corona to Chromosphere and consequences for solar flares
The Astrophysical Journal, 2013Co-Authors: Alex Russell, L FletcherAbstract:How do magnetohydrodynamic waves travel from the fully ionized corona, into and through the underlying partially ionized Chromosphere, and what are the consequences for solar flares? To address these questions, we have developed a two-fluid model (of plasma and neutrals) and used it to perform one-dimensional simulations of Alfven waves in a solar atmosphere with realistic density and temperature structure. Studies of a range of solar features (faculae, plage, penumbra, and umbra) show that energy transmission from corona to Chromosphere can exceed 20% of incident energy for wave periods of 1 s or less. Damping of waves in the Chromosphere depends strongly on wave frequency: waves with periods 10 s or longer pass through the Chromosphere with relatively little damping, however, for periods of 1 s or less, a substantial fraction (37%-100%) of wave energy entering the Chromosphere is damped by ion-neutral friction in the mid- and upper Chromosphere, with electron resistivity playing some role in the lower Chromosphere and in umbras. We therefore conclude that Alfvenic waves with periods of a few seconds or less are capable of heating the Chromosphere during solar flares, and speculate that they could also contribute to electron acceleration or exciting sunquakes.
M Collados - One of the best experts on this subject based on the ideXlab platform.
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tracking downflows from the Chromosphere to the photosphere in a solar arch filament system
The Astrophysical Journal, 2020Co-Authors: Sergio Javier Gonzalez Manrique, M Collados, C Kuckein, Adur Pastor Yabar, A Diercke, P Gomory, Sihui Zhong, C DenkerAbstract:We study the dynamics of plasma along the legs of an arch filament system (AFS) from the Chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrarred Spectrograph (GRIS) in the He I 10830 \r{A} range and the Swedish Solar Telescope (La Palma) using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542 \r{A} and Fe I 6173 \r{A} spectral lines. The temporal evolution of the draining of the plasma was followed along the legs of a single arch filament from the Chromosphere to the photosphere. The average Doppler velocities inferred at the upper Chromosphere from the He I 10830 \r{A} triplet reach velocities up to 20-24~km~s$^{-1}$, in the lower Chromosphere and upper photosphere the Doppler velocities reach up to 11~km~s$^{-1}$ and 1.5~km~s$^{-1}$ in the case of the Ca II 8542 \r{A} and Si I 10827 \r{A} spectral lines, respectively. The evolution of the Doppler velocities at different layers of the solar atmosphere (Chromosphere and upper photosphere) shows that they follow the same LOS velocity pattern, which confirm the observational evidence that the plasma drains towards the photosphere as proposed in models of AFSs. The Doppler velocity maps inferred from the lower photospheric Ca I 10839 \r{A} or Fe I 6173 \r{A} spectral lines do not show the same LOS velocity pattern. Thus, there is no evidence that the plasma reaches the lower photosphere. The observations and the nonlinear force-free field extrapolations demonstrate that the magnetic field loops of the AFS rise with time. We found flow asymmetries at different footpoints of the AFS. The NLFFF values of the magnetic field strength give us a clue to explain these flow asymmetries.
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heating of the magnetized solar Chromosphere by partial ionization effects
The Astrophysical Journal, 2012Co-Authors: E Khomenko, M ColladosAbstract:In this paper, we study the heating of the magnetized solar Chromosphere induced by the large fraction of neutral atoms present in this layer. The presence of neutrals, together with the decrease with height of the collisional coupling, leads to deviations from the classical magnetohydrodynamic behavior of the chromospheric plasma. A relative net motion appears between the neutral and ionized components, usually referred to as ambipolar diffusion. The dissipation of currents in the Chromosphere is enhanced by orders of magnitude due to the action of ambipolar diffusion, as compared with the standard ohmic diffusion. We propose that a significant amount of magnetic energy can be released to the Chromosphere just by existing force-free 10-40 G magnetic fields there. As a consequence, we conclude that ambipolar diffusion is an important process that should be included in chromospheric heating models, as it has the potential to rapidly heat the Chromosphere. We perform analytical estimations and numerical simulations to prove this idea.
Javier Trujillo Bueno - One of the best experts on this subject based on the ideXlab platform.
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on the probable existence of an abrupt magnetization in the upper Chromosphere of the quiet sun
The Astrophysical Journal, 2010Co-Authors: Jiři Stěpan, Javier Trujillo BuenoAbstract:We report on a detailed radiative transfer modeling of the observed scattering polarization in the H{alpha} line, which allows us to infer quantitative information on the magnetization of the quiet solar Chromosphere. Our analysis suggests the presence of a magnetic complexity zone with a mean field strength (B) > 30 G lying just below the sudden transition region to the coronal temperatures. The chromospheric plasma directly underneath is very weakly magnetized, with (B) {approx} 1 G. The possible existence of this abrupt change in the degree of magnetization of the upper Chromosphere of the quiet Sun might have large significance for our understanding of chromospheric (and, therefore, coronal) heating.
Wolfgang Kalkofen - One of the best experts on this subject based on the ideXlab platform.
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Wave heating of the solar Chromosphere
Journal of Astrophysics and Astronomy, 2008Co-Authors: Wolfgang KalkofenAbstract:The nonmagnetic interior of supergranulation cells has been thought since the 1940s to be heated by the dissipation of acoustic waves. But all attempts to measure the acoustic flux have failed to show sufficient energy for chromospheric heating. Recent space observations with TRACE, for example, have found 10% or less of the necessary flux. To explain the missing energy it has been speculated that the nonmagnetic Chromosphere is heated mainly by waves related to the magnetic field. If that were correct, the whole Chromosphere, magnetic as well as nonmagnetic, would be heated mainly by waves related to the magnetic field. But contrary to expectation, the radiation emerging from the nonmagnetic Chromosphere shows none of the signatures of magnetic waves, only those of acoustic waves. Nearly all the heating of the nonmagnetic Chromosphere must therefore be due to acoustic waves. In the magnetic network on the boundary of supergranulation cells, on the other hand, the small filling factor of the magnetic field in the photosphere implies that only a small fraction of the wave flux that travels upward to heat the Chromosphere can be channeled by the magnetic field. Hence, while some of the energy that is dissipated in the magnetic network is in the form of magnetic waves, most of it must be in the form of acoustic waves. Thus, the quiet solar Chromosphere, instead of being heated mainly by magnetic waves throughout, must be heated mainly by acoustic waves throughout. The full wave flux heating the quiet Chromosphere must travel through the photosphere. In the nonmagnetic medium, this flux is essentially all in the form of acoustic waves; TRACE registers at most 10% of it, perhaps because of limited spatial resolution.
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is the solar Chromosphere heated by acoustic waves
The Astrophysical Journal, 2007Co-Authors: Wolfgang KalkofenAbstract:Space observations with TRACE have measured only 10% of the energy flux required to heat the nonmagnetic part of the solar Chromosphere and have thereby called into question the theory of chromospheric heating by acoustic waves. To explain the deficit in the measured flux, heating by processes related to the magnetic field and the limited spatial resolution of the space observations have been invoked. This paper argues that radiation emerging from the nonmagnetic Chromosphere shows that the heating mechanism is dissipation of acoustic waves. The full energy flux required for acoustic heating of the Chromosphere must therefore pass through the photosphere. The explanation of the missing flux by the limited spatial resolution of TRACE confirms the principle of the effect, but the test is preliminary since the hydrodynamic model on which the test is based has temperature fluctuations that far exceed those of the Sun. The shape of the acoustic spectrum observed with TRACE appears to support the theory of wave generation in the solar convection zone. But the low energy flux and the limited acoustic frequency range of the observations prevent a definitive conclusion.
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Heating and dynamics of the quiet solar Chromosphere
Proceedings of the International Astronomical Union, 2007Co-Authors: Wolfgang KalkofenAbstract:The quiet solar Chromosphere in regions with negligible magnetic field is believed to be heated by acoustic waves. But their energy flux, measured in the upper photosphere with the Transition Region And Coronal Explorer (TRACE), has been found to be insufficient to account for the radiative emission from the Chromosphere. Wedemeyer-Bohm et al . (2007) and Cuntz et al . (2007), employing a 3D hydrodynamical model by Wedemeyer et al . (2004), have proposed that the spatial resolution of TRACE is inadequate to resolve intensity fluctuations that occur on small spatial scales. This paper accepts the principle of spatial averaging by TRACE as a qualitative explanation for the low acoustic flux but finds that the hydrodynamical model is too much simplified in the treatment of radiative energy exchange to provide a quantitative measure of the suppression of the fluctuations. The heating mechanism of the Chromosphere thus remains an open question.
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Dynamics and Heating of Chromospheres
Symposium - International Astronomical Union, 2004Co-Authors: Wolfgang KalkofenAbstract:Heating and dynamics of the solar as well as stellar Chromospheres are separate phenomena, judging by their spatial and temporal characteristics in the Sun. Simulations of chromospheric heating in late-type stars as well as simulations of the dynamics of the large-amplitude oscillations of internetwork calcium bright points in the solar atmosphere reproduce the main features of the respective phenomena. Differences between models and observations imply (1) that the Sun has a permanent, hot Chromosphere and that its temperature structure cannot be obtained by averaging the time-dependent temperature profile of a model that describes only the oscillations, and (2) that the acoustic waves causing the dynamics and the heating propagate upward as spherical waves.
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The Near-Infrared Chromosphere Observatory
2002Co-Authors: Barry J. Labonte, David M. Rust, Pietro N. Bernasconi, Manolis K. Georgoulis, Wolfgang KalkofenAbstract:ABSTRACT NICO, the Near Infrared Chromosphere Observatory, is a platform for determining the magnetic structure and sources of heating for the solar Chromosphere. NICO, a balloon-borne observatory, will use the largest solar telescope flying to map the magnetic fields, velocities, and heating events of the Chromosphere and photosphere in detail. NICO will introduce new technologies to solar flight missions, such as wavefront sensing for monitoring telescope alignment, real-time correlation tracking and high-speed image motion compensation, and wide aperture Fabry-Perot etalons for extended spectral scanning. Keywords: solar Chromosphere, solar magnetic fields, high resolution imaging 1. SCIENCE GOALS The solar magnetic field controls the structure, energy flow, mass balance, and eruptive/explosive activity of the solar atmosphere. The science goals for NICO focus on the role of the magnetic field in the solar Chromosphere. This part of the atmosphere has received relatively less attention, but its importance is being more generally recognized. 1. Chromospheric heating Recent solar space missions, including Yohkoh, the Solar and Heliospheric Observatory (SOHO), and the Transition Region and Coronal Explorer (TRACE), focus on the difficult problem of coronal heating. The flux needed to heat the quiet corona is 10