Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: New light on an old problem of the cores of solar resonance lines   We re-examine a 50+ year-old problem of deep central reversals predicted for
strong solar spectral lines, in contrast to the smaller reversals seen in
observations. We examine data and calculations for the resonance lines of H I,
Mg II and Ca II, the self-reversed cores of which form in the upper
chromosphere. Based on 3D simulations as well as data for the Mg II lines from
IRIS, we argue that the resolution lies not in velocity fields on scales in
either of the micro- or macro-turbulent limits. Macro-turbulence is ruled out
using observations of optically thin lines formed in the upper chromosphere,
and by showing that it would need to have unreasonably special properties to
account for critical observations of the Mg II resonance lines from the IRIS
mission. The power in turbulence in the upper chromosphere may therefore be
substantially lower than earlier analyses have inferred. Instead, in 3D
calculations horizontal radiative transfer produces smoother source functions,
smoothing out intensity gradients in wavelength and in space. These effects
increase in stronger lines. Our work will have consequences for understanding
the onset of the transition region, the energy in motions available for heating
the corona, and for the interpretation of polarization data in terms of the
Hanle effect applied to resonance line profiles.

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The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat