Wave-like properties of solar supergranulation

  • An Erratum to this article was published on 13 February 2003

Abstract

Supergranulation1,2 on the surface of the Sun is a pattern of horizontal outflows, outlined by a network of small magnetic features, with a distinct scale of 30 million metres and an apparent lifetime of one day. It is generally believed that supergranulation corresponds to a preferred ‘cellular’ scale of thermal convection; rising magnetic fields are dragged by the outflows and concentrated into ‘ropes’ at the ‘cell’ boundaries3. But as the convection zone is highly turbulent and stratified, numerical modelling has proved to be difficult and the dynamics remain poorly understood. Moreover, there is as yet no explanation for the observation that the pattern appears4,5 to rotate faster around the Sun than the magnetic features. Here we report observations showing that supergranulation undergoes oscillations and supports waves with periods of 6–9 days. The waves are predominantly prograde, which explains the apparent super-rotation of the pattern. The rotation of the plasma through which the pattern propagates is consistent with the motion of the magnetic network.

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Figure 1: Power spectrum of the supergranulation signal near the solar equator (λ = 0°). Sections are shown at constant wavenumber k = 120/R, where R is the solar radius.
Figure 2: Flows, u, inferred from the advection of the supergranulation, plotted against latitude, λ.
Figure 3: Average dynamical properties in a co-moving frame.
Figure 4: Wave power as a function of azimuth and latitude.

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Acknowledgements

We thank D. O. Gough for suggestions about the general presentation of this Letter, and P. Milford, P. H. Scherrer, C. J. Schrijver and N. O. Weiss for comments. SOHO is a mission of international cooperation between the European Space Agency and NASA. MDI is supported by the Office of Space Sciences of NASA.

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Correspondence to L. Gizon.

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Gizon, L., Duvall, T. & Schou, J. Wave-like properties of solar supergranulation. Nature 421, 43–44 (2003). https://doi.org/10.1038/nature01287

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