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Solar physics

Gravity waves with a new spin

Nature volume 388, pages 324–325 (1997)Cite this article

The Sun loses angular momentum to the solar wind via its magnetic field, slowing down the rotation of the outer, convective layers. The core was once thought to be weakly coupled to the outer layers, rotating up to ten or more times faster than the convection zone, but helioseismology has shown that much of the radiative interior rotates at a similar rate to the surface. What couples the two regions so strongly? In two recent papers1,2 wave transport is invoked: gravity waves (similar to internal ocean waves, whose restoring force is buoyancy), generated near the interface between the convective and radiative regions, transport retrograde angular momentum into the interior, thereby spinning it down. Previous estimates3 had cast doubt on the efficacy with which the transport can take place. So what has changed?

The Sun can be divided into two zones, the upper layer where heat transport is by convection, and a lower, stable layer where it is radiative. The angular velocity of the surface decreases with latitude4, the value at the poles being about 70 per cent of that at the equator. Helioseismology — the study of small oscillations in the shape of the Sun — can probe conditions below the surface, and has shown that variation persists down to the base of the convection zone5. Most of the radiative interior rotates almost uniformly at an intermediate rate. The radiative zone is separated from the convection zone by a thin shear layer, called the tachocline6, whose thickness is about 5 per cent of the Sun's radius7.

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Figure 1: A section through the Sun.

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Authors and Affiliations

  1. Institute of Astronomy, The Observatories, University of Cambridge, Madingley Road, CB3 0HA, Cambridge, UK

    Douglas Gough

  2. Department of Applied Mathematics and Theoretical Physics, University of Cambridge,

    Douglas Gough

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  1. Douglas Gough
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Gough, D. Gravity waves with a new spin. Nature 388, 324–325 (1997). https://doi.org/10.1038/40970

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