Ion–neutral Interactions and Nonequilibrium Ionization in the Solar Chromosphere

Martínez-Sykora, Juan; Leenaarts, J.; Pontieu, Bart De; Nóbrega-Siverio, Daniel; Hansteen, V. H.; Carlsson, Mats; Szydlarski, Mikołaj

doi:10.3847/1538-4357/ab643f

Cited by 51 publications

(40 citation statements)

References 56 publications

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“…These may occur as a result of low temperatures in the wake of magneto-acoustic shocks that provide mass to canopy loops. In addition, these simulations show that low-lying transition-region loops could be heated by ambipolar dissipation of electrical currents (Martínez-Sykora et al, 2020a). Further developments of the numerical models (and comparison with observations) thus hold promise to address many unresolved issues, such as the role of the Farley-Buhnemann instability, thermal instabilities (Oppenheim et al, 2020), backwarming from Lyman-α, vorticity and Alfvén waves, interactions between small-scale weak fields and strong network or plage fields, and the interactions between multiple fluids and species (e.g.…”

Section: Ion-neutral Interactionsmentioning

confidence: 81%

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

et al. 2021

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The Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. IRIS is the highest resolution observatory to provide seamless coverage of spectra and images from the photosphere into the low corona. The unique combination of near- and far-ultraviolet spectra and images at sub-arcsecond resolution and high cadence allows the tracing of mass and energy through the critical interface between the surface and the corona or solar wind. IRIS has enabled research into the fundamental physical processes thought to play a role in the low solar atmosphere such as ion–neutral interactions, magnetic reconnection, the generation, propagation, and dissipation of waves, the acceleration of non-thermal particles, and various small-scale instabilities. IRIS has provided insights into a wide range of phenomena including the discovery of non-thermal particles in coronal nano-flares, the formation and impact of spicules and other jets, resonant absorption and dissipation of Alfvénic waves, energy release and jet-like dynamics associated with braiding of magnetic-field lines, the role of turbulence and the tearing-mode instability in reconnection, the contribution of waves, turbulence, and non-thermal particles in the energy deposition during flares and smaller-scale events such as UV bursts, and the role of flux ropes and various other mechanisms in triggering and driving CMEs. IRIS observations have also been used to elucidate the physical mechanisms driving the solar irradiance that impacts Earth’s upper atmosphere, and the connections between solar and stellar physics. Advances in numerical modeling, inversion codes, and machine-learning techniques have played a key role. With the advent of exciting new instrumentation both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST) and the Atacama Large Millimeter/submillimeter Array (ALMA), and space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim to review new insights based on IRIS observations or related modeling, and highlight some of the outstanding challenges.

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Section: Ion-neutral Interactionsmentioning

confidence: 81%

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

et al. 2021

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“…We note that our simulation does not include the effects of ambipolar diffusion, which has been shown to play an important role in 2.5D flux emergence experiments (e.g., Leake & Arber 2006;Martínez-Sykora et al 2020b;Nóbrega-Siverio et al 2020), and it could affect the visibility of different heating events through changes in temperature and density. However, the 2.5D simulation of Martínez-Sykora et al (2020a) that included the effects of ambipolar diffusion and nonequilibrium ionization of helium also suggests that ALMA Band 3 will observe canopy fibrils that originate from strong concentrations of magnetic field, but it predicts low brightness temperatures (∼4500−5000 K) as consequence of expansion of cool dense plasma to much higher heights than in the 3D case (Loukitcheva et al 2015) constituting a cool canopy.…”

Section: Discussionmentioning

confidence: 99%

ALMA observations of transient heating in a solar active region

Santos

Rodríguez

White

et al. 2020

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Aims. We aim to investigate the temperature enhancements and formation heights of solar active-region brightenings such as Ellerman bombs (EBs), ultraviolet bursts (UVBs), and flaring active-region fibrils (FAFs) using interferometric observations in the millimeter (mm) continuum provided by the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We examined 3 mm signatures of heating events identified in Solar Dynamics Observatory observations of an active region and compared the results with synthetic spectra from a 3D radiative magnetohydrodynamic simulation. We estimated the contribution from the corona to the mm brightness using differential emission measure analysis. Results. We report the null detection of EBs in the 3 mm continuum at ∼1.2″ spatial resolution, which is evidence that they are sub-canopy events that do not significantly contribute to heating the upper chromosphere. In contrast, we find the active region to be populated with multiple compact, bright, flickering mm-bursts – reminiscent of UVBs. The high brightness temperatures of up to ∼14 200 K in some events have a contribution (up to ∼7%) from the corona. We also detect FAF-like events in the 3 mm continuum. These events show rapid motions of > 10 kK plasma launched with high plane-of-sky velocities (37 − 340 km s−1) from bright kernels. The mm FAFs are the brightest class of warm canopy fibrils that connect magnetic regions of opposite polarities. The simulation confirms that ALMA should be able to detect the mm counterparts of UVBs and small flares and thus provide a complementary diagnostic for localized heating in the solar chromosphere.

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“…In fact, NEQ ionization and recombination effects of hydrogen are shown to be key for the understanding of the ambipolar diffusion in magnetic flux emergence processes in the Sun (Nóbrega-Siverio et al 2020). In addition, Martínez-Sykora et al (2020a), combining the module presented in this paper together with the two above-mentioned NEQ modules of hydrogen and helium, have shown the important variations in the thermodynamics in the chromosphere and transition region with respect to calculations carried out assuming LTE.…”

Section: Discussionmentioning

confidence: 75%

Ambipolar diffusion in the Bifrost code

Nóbrega-Siverio

Martínez-Sykora

Moreno‐Insertis

et al. 2020

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Context. Ambipolar diffusion is a physical mechanism related to the drift between charged and neutral particles in a partially ionized plasma that is key to many different astrophysical systems. However, understanding its effects is challenging due to basic uncertainties concerning relevant microphysical aspects and the strong constraints it imposes on the numerical modeling. Aims. Our aim is to introduce a numerical tool that allows us to address complex problems involving ambipolar diffusion in which, additionally, departures from ionization equilibrium are important or high resolution is needed. The primary application of this tool is for solar atmosphere calculations, but the methods and results presented here may also have a potential impact on other astrophysical systems. Methods. We have developed a new module for the stellar atmosphere Bifrost code that improves its computational capabilities of the ambipolar diffusion term in the generalized Ohm’s law. This module includes, among other things, collision terms adequate to processes in the coolest regions in the solar chromosphere. As the main feature of the module, we have implemented the super time stepping (STS) technique, which allows an important acceleration of the calculations. We have also introduced hyperdiffusion terms to guarantee the stability of the code. Results. We show that to have an accurate value for the ambipolar diffusion coefficient in the solar atmosphere it is necessary to include as atomic elements in the equation of state not only hydrogen and helium, but also the main electron donors like sodium, silicon, and potassium. In addition, we establish a range of criteria to set up an automatic selection of the free parameters of the STS method that guarantees the best performance, optimizing the stability and speed for the ambipolar diffusion calculations. We validate the STS implementation by comparison with a self-similar analytical solution.

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Ion–neutral Interactions and Nonequilibrium Ionization in the Solar Chromosphere

Cited by 51 publications

References 56 publications

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

ALMA observations of transient heating in a solar active region

Ambipolar diffusion in the Bifrost code

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