Heating of the Magnetized Solar Chromosphere by Partial Ionization Effects

Khomenko, E.; Collados, M.

doi:10.1088/0004-637x/747/2/87

Cited by 168 publications

(217 citation statements)

References 38 publications

(51 reference statements)

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“…In that case, temperature enhancements of +50, +100 and +150 K over the average temperature almost exclusively occur on locations of photospheric magnetic fields. For the two strong magnetic flux concentrations at x ∼ 14.5 Mm and 35 Mm, the temperature enhancements at chromospheric layers above 500 km given by the +50 K contour form exactly the wine-glass shape predicted and used in many photospheric flux tube models (SO91; Pizzo et al 1993;Gadun et al 2001;Khomenko & Collados 2012, their Fig. 10).…”

Section: Visibility and Extent Of Magnetic Canopies In Temperature Mapssupporting

confidence: 62%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2013

A&A

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Context. Most semi-empirical static one-dimensional (1D) models of the solar atmosphere in the magnetically quiet Sun (QS) predict an increase in temperature at chromospheric layers. Numerical simulations of the solar chromosphere with a variable degree of sophistication, i.e. from 1D to three-dimensional (3D) simulations; assuming local thermal equilibrium (LTE) or non-LTE (NLTE), on the other hand, only yielded an increase in the brightness temperature without any stationary increase in the gas temperature.Aims. We investigate the thermal structure in the solar chromosphere as derived from an LTE inversion of observed Ca ii H spectra in QS and active regions (ARs).Methods. We applied an inversion strategy based on the SIR (Stokes inversion by response functions) code to Ca ii H spectra to obtain 1D temperature stratifications. We investigated the temperature stratifications on differences between magnetic and field-free regions in the QS, and on differences between QS and ARs. We determined the energy content of individual calcium bright grains (BGs) as specific candidates of chromospheric heating events. We compared observed with synthetic NLTE spectra to estimate the significance of the LTE inversion results. Results. The fluctuations of observed intensities yield a variable temperature structure with spatio-temporal rms fluctuations below 100 K in the photosphere and between 200 and 300 K in the QS chromosphere. The average temperature stratification in the QS does not exhibit a clear chromospheric temperature rise, unlike the AR case. We find a characteristic energy content of about 7 × 10 18 J for BGs that repeat with a cadence of about 160 s. The precursors of BGs have a vertical extent of about 200 km and a horizontal extent of about 1 Mm. The comparison of observed with synthetic NLTE profiles partly confirms the results of the LTE inversion that the solar chromosphere in the QS oscillates between an atmosphere in radiative equilibrium and one with a moderate chromospheric temperature rise. Two-dimensional x − z temperature maps exhibit nearly horizontal canopy-like structures with an extent of a few Mm around photospheric magnetic field concentrations at a height of about 600 km. Conclusions. The large difference between QS regions and ARs and the better match of AR and NLTE reference spectra suggest that magnetic heating processes are more important than commonly assumed. The temperature fluctuations in QS derived by the LTE inversion do not suffice on average to maintain a stationary chromospheric temperature rise. The spatially and vertically resolved information on the temperature structure allows one to investigate in detail the topology and evolution of the thermal structure in the lower solar atmosphere.

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Section: Visibility and Extent Of Magnetic Canopies In Temperature Mapssupporting

confidence: 62%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2013

A&A

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“…(15) is very difficult. Hence, we first concentrate in the modifications introduced in the ideal MHD theory by the ambipolar term, which has proved to be relevant in solar atmospheric situations (see for example Khodachenko et al 2004;Arber et al 2007;Khomenko & Collados 2012, and references therein). We neglect all the magnetic diffusion terms in this section except the ambipolar one, obtaining a simple form of the induction equation,…”

Section: Mhd and Ambipolar Diffusionmentioning

confidence: 99%

Rayleigh-Taylor instability in partially ionized compressible plasmas: One fluid approach

Díaz

Khomenko

Collados

2014

A&A

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Aims. We study the modification of the classical criterion for the linear onset and growth rate of the Rayleigh-Taylor instability (RTI) in a partially ionized (PI) plasma in the one-fluid description by considering a generalized induction equation. Methods. The governing linear equations and appropriate boundary conditions, including gravitational terms, are derived and applied to the case of the RTI in a single interface between two partially ionized plasmas. The boundary conditions lead to an equation for the frequencies in which some have positive complex parts, marking the appearance of the RTI. We study the ambipolar term alone first, extending the result to the full induction equation later. Results. The configuration is always unstable because of the presence of a neutral species. In the classical stability regime, the growth rate is small, since the collisions prevent the neutral fluid to fully develop the RTI. For parameters in the classical instability regime, the growth rate is lowered, but the differences with the compressible MHD case are small for the considered theoretical values of the collision frequencies and diffusion coefficients for solar prominences. Conclusions. The PI modifies some aspects of the linear RTI instability, since it takes into account that neutrals do not feel the stabilizing effect of the magnetic field. For the set of parameters representative for solar prominences, our model gives the resulting timescale comparable to observed lifetimes of RTI plumes.

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“…The ionisation degree of prominences is not well known, but there is plentiful evidence that this cannot be neglected when one studies the dynamics and stability of these structures (Patsourakos & Vial 2002;Gilbert et al 2002;Carbonell et al 2010;Labrosse et al 2010;Zaqarashvili et al 2012;Khomenko & Collados 2012;Soler et al 2013, etc. ).…”

Section: Introductionmentioning

confidence: 99%

Dissipative instability in partially ionised prominence plasmas

Ballai

Oliver

Alexandrou

2015

A&A

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Aims. We investigate the nature of dissipative instability at the boundary (seen here as tangential discontinuity) between the viscous corona and the partially ionised prominence plasma in the incompressible limit. The importance of the partial ionisation is investigated in terms of the ionisation fraction. Methods. Matching the solutions for the transversal component of the velocity and total pressure at the interface between the prominence and coronal plasmas, we derive a dispersion relation whose imaginary part describes the evolution of the instability. Results are obtained in the limit of weak dissipation. Results. Using simple analytical methods, we show that dissipative instabilities appear for flow speeds that are lower than the Kelvin-Helmholtz instability threshold. While viscosity tends to destabilise the plasma, the effect of partial ionisation (through the Cowling resistivity) will act towards stabilising the interface. For ionisation degrees closer to a neutral gas the interface will be unstable for larger values of equilibrium flow. The same principle is assumed when studying the appearance of instability at the interface between prominences and dark plumes. The unstable mode appearing in this case has a very small growth rate and dissipative instability cannot explain the appearance of flows in plumes.Conclusions. The present study improves our understanding of the complexity of dynamical processes at the interface of solar prominences and solar corona, and the role partial ionisation can have on the stability of the plasma. Our results clearly show that the problem of partial ionisation introduces new aspects of plasma stability with consequences on the evolution of solar prominences.

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Heating of the Magnetized Solar Chromosphere by Partial Ionization Effects

Cited by 168 publications

References 38 publications

The energy of waves in the photosphere and lower chromosphere

The energy of waves in the photosphere and lower chromosphere

Rayleigh-Taylor instability in partially ionized compressible plasmas: One fluid approach

Dissipative instability in partially ionised prominence plasmas

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