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A subsurface flow of material from the Sun's equator to its poles

Nature volume 390, pages 52–54 (1997)Cite this article

Abstract

Gas on the Sun's surface has been observed1,2,3,4 to flow away from the equator towards both poles. If the same flow persists to great depths, it could play an important dynamical role in the eleven-year sunspot cycle, by carrying the magnetic remnants of the sunspots to high latitudes5. An even deeper counterflow, which would be required to maintain mass balance, could explain why new sunspots form at lower latitudes as the cycle progresses6. These deep flows would also redistribute angular momentum within the Sun, and therefore help to maintain the faster rotation of the equator relative to the poles7. Here we report the detection, using helioseismic tomography, of the longitude-averaged subsurface flow in the outer 4% of the Sun. We find that the subsurface flow is approximately constant in this depth range, and that the speed is similar to that seen on the surface. This demonstrates that the surface flow penetrates deeply, so that it is likely to be an important factor in solar dynamics.

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Figure 1: Diagram showing the geometry of the analysis.
Figure 2: The average travel time difference (south minus north) for surface separation of pairs of points in the range 12–73 × 106 m.
Figure 3: The fit coefficients a 2 (a) and a 1 (b) plotted against the distance Δ.

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Acknowledgements

T.D. thanks Phil Scherrer and the SOI group at Stanford for their hospitality during this work and for the use of their computing facilities, supported by a contract from NASA. This work was supported in part by the Solar Physics Branch of the Space Physics Division of NASA. SOHO is a mission of international cooperation between ESA and NASA.

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Authors and Affiliations

  1. Department of Applied Physics, Stanford University, Stanford, 94305-4085, California, USA

    P. M. Giles

  2. Laboratory for Astronomy and Solar Physics, NASA/Goddard Space Flight Center, Greenbelt, 20771, Maryland, USA

    T. L. Duvall Jr

  3. W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, 94305-4085, California, USA

    P. H. Scherrer & R. S. Bogart

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  1. P. M. Giles
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Correspondence to P. M. Giles.

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Giles, P., Duvall, T., Scherrer, P. et al. A subsurface flow of material from the Sun's equator to its poles. Nature 390, 52–54 (1997). https://doi.org/10.1038/36294

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