Approximations for radiative cooling and heating in the solar chromosphere

Carlsson, Mats; Leenaarts, J.

doi:10.1051/0004-6361/201118366

Cited by 185 publications

(165 citation statements)

References 42 publications

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“…R is the optically thin radiative emission, which can be calculated using a set of piecewise power laws, a fit to radiative loss curves calculated by the Chianti atomic database for equilibrium ionization or a full non-equilibrium treatment of the radiating ions (thermal bremmstrahlung is also included in the calculation). R can also be calculated for optically thick conditions in the lower atmosphere using the treatment given by Carlsson & Leenaarts (2012) and in this case the presence of neutral species is accounted for (e.g., number density of neutrals, ions, and electrons, inter-species collisions, thermal conduction of neutral hydrogen). However, in the present work the chromosphere is maintained at a uniform temperature (20,000 K) by reducing the optically thin radiative losses to zero over a specified temperature interval (100 K) above the chromospheric temperature (Klimchuk et al 1987).…”

Section: A1 the Hydrodynamic Equationsmentioning

confidence: 99%

The Influence of Numerical Resolution on Coronal Density in Hydrodynamic Models of Impulsive Heating

Bradshaw

Cargill

2013

ApJ

129

122

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The effect of the numerical spatial resolution in models of the solar corona and corona/chromosphere interface is examined for impulsive heating over a range of magnitudes using one-dimensional hydrodynamic simulations. It is demonstrated that the principal effect of inadequate resolution is on the coronal density. An underresolved loop typically has a peak density of at least a factor of two lower than a resolved loop subject to the same heating, with larger discrepancies in the decay phase. The temperature for underresolved loops is also lower indicating that lack of resolution does not "bottle up" the heat flux in the corona. Energy is conserved in the models to under 1% in all cases, indicating that this is not responsible for the low density. Instead, we argue that in underresolved loops the heat flux "jumps across" the transition region to the dense chromosphere from which it is radiated rather than heating and ablating transition region plasma. This emphasizes the point that the interaction between corona and chromosphere occurs only through the medium of the transition region. Implications for three-dimensional magnetohydrodynamic coronal models are discussed.

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Section: A1 the Hydrodynamic Equationsmentioning

confidence: 99%

The Influence of Numerical Resolution on Coronal Density in Hydrodynamic Models of Impulsive Heating

Bradshaw

Cargill

2013

ApJ

129

122

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“…As a result, it is important to repeat dynamic simulations such as those of WE04 and Carlsson & Stein (1997) that include magnetic fields. Basically all chromospheric simulations to date share simplifications regarding the topology or presence of small-scale magnetic fields, scattering, time-dependent hydrogen ionization, as well as the NLTE radiative transfer (Carlsson & Leenaarts 2012). …”

Section: Semi-empirical Vs Dynamic Chromospheric Modelsmentioning

confidence: 99%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2012

A&A

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Context. The energy source powering the solar chromosphere is still undetermined, but leaves its traces in observed intensities. Aims. We investigate the statistics of the intensity distributions as a function of the wavelength for Ca ii H and the Ca ii IR line at 854.2 nm to estimate the energy content in the observed intensity fluctuations. Methods. We derived the intensity variations at different heights of the solar atmosphere, as traced by the line wings and line cores of the two spectral lines. We converted the observed intensities to absolute energy units employing reference profiles calculated in non-local thermal equilibrium (NLTE). We also converted the intensity fluctuations to corresponding brightness temperatures assuming LTE. Results. The root-mean-square (rms) fluctuations of the emitted intensity are about 0.6 (1.2) W m −2 ster −1 pm −1 near the core of the Ca ii IR line at 854.2 nm (Ca ii H), corresponding to relative intensity fluctuations of about 20% (30%). For the line wing, we find rms values of about 0.3 W m −2 ster −1 pm −1 for both lines, corresponding to relative fluctuations below 5%. The relative rms values show a local minimum for wavelengths forming at a height of about 130 km, but otherwise increase smoothly from the wing to the core, i.e., from photosphere to chromosphere. The corresponding rms brightness temperature fluctuations are below 100 K for the photosphere and up to 500 K in the chromosphere. The skewness of the intensity distributions is close to zero in the outer line wing and positive throughout the rest of the line spectrum, owing to the frequent occurrence of high-intensity events. The skewness shows a pronounced local maximum at locations with photospheric magnetic fields for wavelengths in-between those of the line wing and the line core (z ≈ 150−300 km), and a global maximum at the very core (z ≈ 1000 km) for both magnetic and field-free locations. Conclusions. The energy content of the intensity fluctuations is insufficient to create a chromospheric temperature rise that would be similar to the one in most reference models of the solar atmosphere. The increase in the rms fluctuations with height indicates the presence of upwardly propagating acoustic waves of increasing oscillation amplitude. The intensity and temperature variations indicate that there is a clear increase in dynamical activity from photosphere towards the chromosphere, but the variations fall short of the magnitude predicted by fully dynamical chromospheric models by a factor of about five. The enhanced skewness between the photosphere and lower solar chromosphere at magnetic locations is indicative of a mechanism that acts solely on magnetized plasma.

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“…] and SYNSPEC [32]. Another one is to use more physical escape probabilities [33]. Radiation parameters in this work (energy, flux and opacities) are integrated over all frequencies.…”

Section: Conclusion and Prospectsmentioning

confidence: 99%

Accretion shock stability on a dynamically heated YSO atmosphere with radiative transfer

Sá

Chièze

Stehlé

et al. 2014

EPJ Web of Conferences

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Abstract. Theory and simulations predict Quasi-Periodic Oscillations of shocks which develop in magnetically driven accretion funnels connecting the stellar disc to the photosphere of Young Stellar Objects (YSO). X-ray observations however do not show evidence of the expected periodicity. We examine here, in a first attempt, the influence of radiative transfer on the evolution of material impinging on a dynamically heated stellar atmosphere, using the 1D ALE-RHD code ASTROLABE. The mechanical shock heating mechanism of the chromosphere only slightly perturbs the flow. We also show that, since the impacting flow, and especially the part which penetrates into the chromosphere, is not treated as a purely radiating transparent medium, a sufficiently efficient coupling between gas and radiation may affect or even suppress the oscillations of the shocked column. This study shows the importance of the description of the radiation effects in the hydrodynamics and of the accuracy of the opacities for an adequate modeling.

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Approximations for radiative cooling and heating in the solar chromosphere

Cited by 185 publications

References 42 publications

The Influence of Numerical Resolution on Coronal Density in Hydrodynamic Models of Impulsive Heating

The Influence of Numerical Resolution on Coronal Density in Hydrodynamic Models of Impulsive Heating

The energy of waves in the photosphere and lower chromosphere

Accretion shock stability on a dynamically heated YSO atmosphere with radiative transfer

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