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Rossby waves on the Sun as revealed by solar ‘hills’

Nature volume 405, pages 544–546 (2000)Cite this article

Abstract

It is a long-standing puzzle that the Sun's photosphere—its visible surface—rotates differentially, with the equatorial regions rotating faster than the poles. It has been suggested1 that waves analogous to terrestrial Rossby waves, and known as r-mode oscillations, could explain the Sun's differential rotation: Rossby waves are seen2 in the oceans as large-scale (hundreds of kilometres) variations of sea-surface height (5-cm-high waves), which propagate slowly either east or west (they could take tens of years to cross the Pacific Ocean). Calculations show that the solar r-mode oscillations have properties that should be strongly constrained by differential rotation3. Here we report the detection of 100-m-high ‘hills’ in the photosphere, spaced uniformly over the Sun's surface with a spacing of (8.7 ± 0.6) × 104 km. If convection under the photosphere is organized by the r-modes, the observed corrugated photosphere is a probable surface manifestation of these solar oscillations.

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Figure 1: The two-dimensional power spectrum of the limb displacement.
Figure 2: The two-dimensional, low-frequency, power spectrum of the MDI limb timeseries.
Figure 3: Root-mean-square limb shape velocity amplitude plotted against frequency.
Figure 4: The power distribution plotted here shows the average power per temporal frequency bin versus position angle.
Figure 5: The mean power spectrum averaged over solar latitude.

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Acknowledgements

We thank J. Saba, C. DeForest and J. Covington for assistance in operating the MDI instrument during these observations. We are particularly grateful to R. Bogart and to X. Scheick for their help with the limb software analysis.

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Authors and Affiliations

  1. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, 96822, Hawaii, USA

    J. R. Kuhn & J. D. Armstrong

  2. Stanford University, HEPL 4085, Stanford, 94305, California, USA

    R. I. Bush & P. Scherrer

Authors
  1. J. R. Kuhn
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  2. J. D. Armstrong
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  4. P. Scherrer
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Correspondence to J. R. Kuhn.

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Kuhn, J., Armstrong, J., Bush, R. et al. Rossby waves on the Sun as revealed by solar ‘hills’. Nature 405, 544–546 (2000). https://doi.org/10.1038/35014530

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