A basal contribution from p-modes to the Alfvénic wave flux in the Sun’s corona

Abstract

Many cool stars possess complex magnetic fields1 that are considered to undertake a central role in the structuring and energizing of their atmospheres2. Alfvénic waves are thought to make a critical contribution to energy transfer along these magnetic fields, with the potential to heat plasma and accelerate stellar winds3,4,5. Despite Alfvénic waves having been identified in the Sun’s atmosphere, the nature of the basal wave energy flux is poorly understood. It is generally assumed that the associated Poynting flux is generated solely in the photosphere and propagates into the corona, typically through the continuous buffeting of magnetic fields by turbulent convective cells4,6,7. Here, we provide evidence that the Sun’s internal acoustic modes also contribute to the basal flux of Alfvénic waves, delivering a spatially ubiquitous input to the coronal energy balance that is sustained over the solar cycle. Alfvénic waves are thus a fundamental feature of the Sun’s corona. Acknowledging that internal acoustic modes have a key role in injecting additional Poynting flux into the upper atmospheres of Sun-like stars has potentially significant consequences for the modelling of stellar coronae and winds.

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Fig. 1: Signature of coronal Alfvénic waves.
Fig. 2: Properties of Alfvénic waves throughout the corona.
Fig. 3: Power spectra parameter distributions for Alfvénic waves.
Fig. 4: Global measures of Alfvénic waves through the solar cycle.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. The SDO data are available from the Joint Science Operations Center (http://jsoc.stanford.edu). The CoMP data are available from the High Altitude Observatory data repository (https://www2.hao.ucar.edu/mlso/mlso-home-page).

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Acknowledgements

All authors acknowledge that this material is based on work supported by the Air Force Office of Scientific Research, Air Force Material Command, USAF under award number FA9550-16-1-0032, and the Science and Technology Facilities Council via grant number ST/L006243/1. R.J.M. is grateful to the Leverhulme Trust for the award of an Early Career Fellowship, and the High Altitude Observatory for financial assistance. M.J.W. acknowledges additional support from NASA grant NNH16AC39I and basic research funds from the Chief of Naval Research. R.J.M. is also grateful for discussions at ISSI, Bern (Towards Dynamic Solar Atmospheric Magneto-Seismology with New Generation Instrumentation) and with G. Li and S. Tomczyk. The authors acknowledge the work of the NASA/SDO and AIA science teams, and National Center for Atmospheric Research/High Altitude Observatory CoMP instrument team.

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R.J.M. performed the analysis of the CoMP data. R.J.M., M.J.W. and J.A.M. performed the analysis of the SDO data. All authors discussed the results and contributed to the writing of the manuscript.

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Correspondence to R. J. Morton.

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Supplementary Text, Supplementary Tables 1–3, Supplementary References

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Morton, R.J., Weberg, M.J. & McLaughlin, J.A. A basal contribution from p-modes to the Alfvénic wave flux in the Sun’s corona. Nat Astron 3, 223–229 (2019). https://doi.org/10.1038/s41550-018-0668-9

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