Bibcode
Beck, C. A. R.; Rammacher, W.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 510, id.A66
Advertised on:
2
2010
Revista
Número de citas
5
Número de citas referidas
5
Descripción
Context. The process that heats the solar chromosphere is a difficult
target for observational studies because the assumption of local thermal
equilibrium (LTE) is not valid in the upper solar atmosphere, which
complicates the analysis of spectra. Aims: We investigate the
linear correlation coefficient between the intensities at different
wavelengths in photospheric and chromospheric spectral lines because the
correlation can be determined directly for any spectra from observations
or modeling. Waves which propagate vertically through the stratified
solar atmosphere affect different wavelengths at different times when
the contribution functions for each wavelength peak in different layers.
This leads to a characteristic pattern of (non-)coherence of the
intensity at various wavelengths with respect to each other which
carries information on the physical processes. Methods: We
derived the correlation matrices for several photospheric and
chromospheric spectral lines from observations. We separated locations
with a significant photospheric polarization signal and thus magnetic
fields from those without a polarization signal. For comparison with the
observations, we calculated correlation matrices for spectra from
simplified LTE modeling approaches, 1-D NLTE simulations, and a 3-D MHD
simulation run. We applied the correlation method also to temperature
maps at different optical depth layers derived from a LTE inversion of
Ca II H spectra. Results: We find that all photospheric spectral
lines show a similar pattern: a pronounced asymmetry of the correlation
between line core and red or blue wing. The pattern cannot be reproduced
with a simulation of the granulation pattern, but with waves that travel
upwards through the formation heights of the lines. The correct
asymmetry between red and blue wing only appears when a temperature
enhancement occurs simultaneously with a downflow velocity in the wave
simulation. All chromospheric spectral lines show a more complex
pattern. The 1-D NLTE simulations of monochromatic waves produce a
correlation matrix that qualitatively matches the observations near the
very core of the Ca II H line. The photospheric signature is well
reproduced in the correlation matrix derived from the 3-D MHD
simulation. Conclusions: The correlation matrices of observed
photospheric and chromospheric spectral lines are highly structured with
characteristic and different patterns in every spectral line. The
comparison with matrices derived from simulations and simple modeling
suggests that the main driver of the detected patterns are upwards
propagating waves. Application of the correlation method to 3-D
temperature cubes seems to be a promising tool for a detailed comparison
of simulation results and observations in future studies.
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