Signatures of photospheric convection throughout the solar atmosphere: the EVE Sun-as-a-star mHz continuum
4 affiliations
- 1SUPA School of Physics & Astronomy, University of Glasgow , Glasgow G12 8QQ ,
- 2Space Science Laboratory, University of California , Berkeley, CA 94720 ,
- 3Centre for Fusion, Space, and Astrophysics, University of Warwick , Coventry, CV4 7AL ,
- 4Rosseland Centre for Solar Physics, University of Oslo , PO Box 1029 Blindern, NO-0315 Oslo ,
Abstract
Convectively driven motions in the solar photosphere can generate broad-band Doppler variability across the chromosphere, transition region, and corona. Here, we investigate this variability using ‘Sun-as-a-star’ observations from the Extreme Ultraviolet Variability Experiment (EVE) aboard the Solar Dynamics Observatory, constructing high signal-to-noise Doppler power spectra by incoherently averaging spectra from 3-h sequences of the centroid wavelengths of emission lines that span wavelengths 35–104 nm. The spectra reveal a broad power-spectral continuum with two ‘Harvey’ components, one of which extends to the Nyquist frequency at 50 mHz with a steep power-law tail. All emission lines have substantial power both above and below the nominal acoustic cutoff frequency at 5 mHz, but none of the power spectra show maxima corresponding to p-mode or chromospheric 3-min oscillations. Lines formed in the corona, as compared with those of the chromosphere/transition region, have substantially less Doppler amplitude in the Harvey spectrum associated with granulation-scale convection. Based on the observed continuum, there is no evidence (in any of the 26 lines studied) for Kolmogorov turbulence, which predicts a flat continuum component with Doppler variance ⟨ v2⟩ ∝ f−5/3 as a function of frequency f. The total inferred RMS velocities (gt 0.1 mHz) are roughly consistent with coronal ‘microturbulence’ estimates from excess line widths. These observations provide the first clear detection of Sun-as-a-star extreme ultraviolet (EUV) Doppler variability above ∼10 mHz and demonstrate the potential of full-disc EUV spectroscopy to probe turbulent energy transport throughout a stellar atmosphere. The predominance of the Harvey spectrum, a signature of photospheric convection, likely results from limb brightening of the Doppler variance due to horizontal flows in the upper solar atmosphere.
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BibTeX
@article{hudson2026signatures,
title = {{Signatures of photospheric convection throughout the solar atmosphere: the EVE Sun-as-a-star mHz continuum}},
author = {Hugh Hudson and Anne-Marie Broomhall and Lyndsay Fletcher and David Graham and Sargam M Mulay and Chris Osborne and Kirsty Williamson and Graham Woan},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1903},
url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1903/8876086},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Signatures of photospheric convection throughout the solar atmosphere: the EVE Sun-as-a-star mHz continuum
AU - Hugh Hudson
AU - Anne-Marie Broomhall
AU - Lyndsay Fletcher
AU - David Graham
AU - Sargam M Mulay
AU - Chris Osborne
AU - Kirsty Williamson
AU - Graham Woan
PY - 2026
DA - 2026/10/07
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1903
UR - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1903/8876086
AB - Convectively driven motions in the solar photosphere can generate broad-band Doppler variability across the chromosphere, transition region, and corona. Here, we investigate this variability using ‘Sun-as-a-star’ observations from the Extreme Ultraviolet Variability Experiment (EVE) aboard the Solar Dynamics Observatory, constructing high signal-to-noise Doppler power spectra by incoherently averaging spectra from 3-h sequences of the centroid wavelengths of emission lines that span wavelengths 35–104 nm. The spectra reveal a broad power-spectral continuum with two ‘Harvey’ components, one of which extends to the Nyquist frequency at 50 mHz with a steep power-law tail. All emission lines have substantial power both above and below the nominal acoustic cutoff frequency at 5 mHz, but none of the power spectra show maxima corresponding to p-mode or chromospheric 3-min oscillations. Lines formed in the corona, as compared with those of the chromosphere/transition region, have substantially less Doppler amplitude in the Harvey spectrum associated with granulation-scale convection. Based on the observed continuum, there is no evidence (in any of the 26 lines studied) for Kolmogorov turbulence, which predicts a flat continuum component with Doppler variance ⟨ v^2⟩ ∝ f^−5/3 as a function of frequency f. The total inferred RMS velocities (gt 0.1 mHz) are roughly consistent with coronal ‘microturbulence’ estimates from excess line widths. These observations provide the first clear detection of Sun-as-a-star extreme ultraviolet (EUV) Doppler variability above ∼10 mHz and demonstrate the potential of full-disc EUV spectroscopy to probe turbulent energy transport throughout a stellar atmosphere. The predominance of the Harvey spectrum, a signature of photospheric convection, likely results from limb brightening of the Doppler variance due to horizontal flows in the upper solar atmosphere.
SN - 0035-8711
SN - 1365-2966
ER -