Emission measures, electron densities, and nonthermal velocities from optically thin UV lines near a quiet solar limb

Moe, O. Kjeldseth; Nicolas, K. R.

doi:10.1086/154966

Cited by 76 publications

(30 citation statements)

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“…The largest blue-ward asymmetries are for transition region EUV profiles [16][17][18][19][20][21][22]. Martínez-Sykora et al [15] find that the synthetic RB analysis of various EUV lines from their simulations reproduces, qualitatively, the observations taken by Solar Ultraviolet Measurements of Emitted Radiation [23] on board of the Solar and Heliospheric Observatory [24] and the EUV Imaging Spectrometer [25] on board of Hinode [26].…”

Section: Coronal Heating Versus Heating Concentrated In the Low Atmosmentioning

confidence: 90%

The role of partial ionization effects in the chromosphere

Martínez-Sykora

Pontieu

Hansteen

et al. 2015

Phil. Trans. R. Soc. A.

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The energy for the coronal heating must be provided from the convection zone. However, the amount and the method by which this energy is transferred into the corona depend on the properties of the lower atmosphere and the corona itself. We review: (i) how the energy could be built in the lower solar atmosphere, (ii) how this energy is transferred through the solar atmosphere, and (iii) how the energy is finally dissipated in the chromosphere and/or corona. Any mechanism of energy transport has to deal with the various physical processes in the lower atmosphere. We will focus on a physical process that seems to be highly important in the chromosphere and not deeply studied until recently: the ionneutral interaction effects in the chromosphere. We review the relevance and the role of the partial ionization in the chromosphere and show that this process actually impacts considerably the outer solar atmosphere. We include analysis of our 2.5D radiative magnetohydrodynamic simulations with the Bifrost code (Gudiksen et al.

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Section: Coronal Heating Versus Heating Concentrated In the Low Atmosmentioning

confidence: 90%

The role of partial ionization effects in the chromosphere

Martínez-Sykora

Pontieu

Hansteen

et al. 2015

Phil. Trans. R. Soc. A.

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“…A statistical analysis shows that the redshift tends to be stronger for brighter individual profiles (Brynildsen et al 1998). As for the profile, Kjeldseth Moe & Nicolas (1977) were the first to notice a second Gaussian component in the enhanced wings of the transition region spectral lines.…”

Section: Introductionmentioning

confidence: 87%

Sizes of quiet Sun transition region structures

Gontikakis¹,

Peter²,

Dara³

2003

A&A

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Abstract.We studied the morphology of the transition region of the quiet Sun, with data obtained by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer (SUMER) and the Extreme-Ultraviolet Imaging Telescope (EIT), in September 1996. We analyzed lines emitted in the chromosphere, the low transition region and the low corona. We computed the mean autocorrelation function for the radiance images in order to estimate the characteristic size of the features present in the transition region. Moreover, we calculated autocorrelation functions for the dopplergrams and line width images deduced from the SUMER data. In addition to the line core of the C  line, we investigated a broader tail component, whose origin is still unclear. We found that the size of the bright radiance features is always larger than the size of the structures of the dopplergrams and Doppler widths, at any altitude. The network features seem to diminish at a temperature around 10 5 K, due to the thermodynamic properties of the transition region. The mean size of the structures of the tail component radiance is smaller than the one of the core radiance.

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“…A comprehensive list of these velocities will not be attempted here, but a few examples of reported upflow and downflow velocities obtained by measuring relative doppler shifts or those inferred from broadened line widths of optically thin lines are: 10-150 km s -1 for macrospicules (Bohlin et al, 1975), 30 to several hundred km S -1 for transition region lines and 5 to 15 km s -1 for coronal lines (Brueckner et al, 1977), 16 km s -1 (average) for coronal emission lines (Cushman and Rense, 1976), 16 to 28 km s -1 for chromospheric lines (Doschek etaI., 1976), 11 to 26 km s -~ for chromospheric lines (Boland et al, 1975), and 20-25 km s -1 for most optically thin chromospheric and transition zone lines but 45-75 km s -I for some transition zone lines (Moe and Nicolas, 1977). In view of these high velocities reported for solar emission lines and the steep temperature gradients thus far inferred for the transition region, the validity of ionization equilibrium should not be taken for granted.…”

Section: Introductionmentioning

confidence: 99%

Mass flow and the validity of ionization equilibrium on the Sun

1979

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Ionization equilibrium is a useful assumption which allows temperatures and other plasma properties to be deduced from spectral observations. Inherent to this assumption is the premise that the ion stage densities are determined solely by atomic processes which are local functions of the plasma temperature and electron density. However, if the time scale of plasma flow through a temperature gradient is less than the characteristic time scale for an important atomic process, deviations from the ionization stage densities expected for equilibrium will occur which could introduce serious errors into subsequent analyses. In the past few years, significant flow velocities in the upper solar atmosphere have been inferred from observations of emission lines originaing in the transition region (about 104-106 K) and corona. In this paper, three models of the solar atmosphere (quiet Sun, coronal hole, and a network model) are examined to determine if the emission expected from these model atmospheres could be produced from equilibrium ion populations when steady flows of several kilometers per second are assumed. If the flows are quasi-periodic instead of steady, spatial and temporal averaging inherent in the observations may allow for the construction of satisfactory models based on the assumption of ionization equilibrium. Representative emission lines are analysed for the following ions: C III, Iv, O Iv, v, vI, Ne vii, viii, Mg Ix, x, Si xu, and Fe rx-xIv. Two principle conclusions are drawn. First, only the iron ions are generally in equilibrium for steady flows of 20 km s -1. For carbon and oxygen, ionization equilibrium is not a valid assumption for steady flows as small as 1 km s -1. Second, the three models representing different solar conditions behave in a qualitatively similar manner, implying that these results are not particularly model dependent over the range of temperature gradients and electron densities thus far inferred for the Sun. In view of the flow velocities which have been reported for the Sun, our results strongly suggest caution in using the assumption of ionization equilibrium for interpreting spectral lines produced in the transition region.

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Emission measures, electron densities, and nonthermal velocities from optically thin UV lines near a quiet solar limb

Cited by 76 publications

References 0 publications

The role of partial ionization effects in the chromosphere

The role of partial ionization effects in the chromosphere

Sizes of quiet Sun transition region structures

Mass flow and the validity of ionization equilibrium on the Sun

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