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  Power spectrum of turbulent convection in the solar photosphere

Chaouche, L. Y., Cameron, R. H., Solanki, S. K., Riethmüller, T., Anusha, L. S., Witzke, V., et al. (2020). Power spectrum of turbulent convection in the solar photosphere. Astronomy and Astrophysics, 644: A44. doi:10.1051/0004-6361/202037545.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0007-A827-0 Version Permalink: http://hdl.handle.net/21.11116/0000-0007-A828-F
Genre: Journal Article

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 Creators:
Chaouche, L. Yelles, Author
Cameron, Robert H.1, Author              
Solanki, Sami K.1, Author              
Riethmüller, Tino1, Author              
Anusha, L. S.1, Author              
Witzke, Veronika1, Author              
Shapiro, Alexander1, Author              
Barthol, Peter1, Author              
Gandorfer, Achim M.1, Author              
Gizon, Laurent2, Author              
Hirzberger, Johann1, Author              
van Noort, Michiel1, Author              
Rodríguez, J. Blanco, Author
Iniesta, J. C. Del Toro, Author
Suárez, D. Orozco, Author
Schmidt, W., Author
Pillet, V. Martínez, Author
Knölker, M., Author
Affiliations:
1Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289              
2Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              

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Free keywords: Sun: photosphere / turbulence / convection
 Abstract: The solar photosphere provides us with a laboratory for understanding turbulence in a layer where the fundamental processes of transport vary rapidly and a strongly superadiabatic region lies very closely to a subadiabatic layer. Our tools for probing the turbulence are high-resolution spectropolarimetric observations such as have recently been obtained with the two balloon-borne SUNRISE missions, and numerical simulations. Our aim is to study photospheric turbulence with the help of Fourier power spectra that we compute from observations and simulations. We also attempt to explain some properties of the photospheric overshooting flow with the help of its governing equations and simulations. We find that quiet-Sun observations and smeared simulations are consistent with each other and exhibit a power-law behavior in the subgranular range of their Doppler velocity power spectra with a power-law index of ≈ − 2. The unsmeared simulations exhibit a power law that extends over the full range between the integral and Taylor scales with a power-law index of ≈ − 2.25. The smearing, reminiscent of observational conditions, considerably reduces the extent of the power-law-like portion of the power spectra. This suggests that the limited spatial resolution in some observations might eventually result in larger uncertainties in the estimation of the power-law indices. The simulated vertical velocity power spectra as a function of height show a rapid change in the power-law index (at the subgranular range) from roughly the optical depth unity layer, that is, the solar surface, to 300 km above it. We propose that the cause of the steepening of the power-law index is the transition from a super- to a subadiabatic region, in which the dominant source of motions is overshooting convection. A scale-dependent transport of the vertical momentum occurs. At smaller scales, the vertical momentum is more efficiently transported sideways than at larger scales. This results in less vertical velocity power transported upward at small scales than at larger scales and produces a progressively steeper vertical velocity power law below 180 km. Above this height, the gravity work progressively gains importance at all relevant scales, making the atmosphere progressively more hydrostatic and resulting in a gradually less steep power law. Radiative heating and cooling of the plasma is shown to play a dominant role in the plasma energetics in this region, which is important in terms of nonadiabatic damping of the convective motions.

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Language(s): eng - English
 Dates: 2020
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/202037545
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Affiliations:
Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 644 Sequence Number: A44 Start / End Page: - Identifier: ISSN: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1