The Sun's Magnetic Field (2) ...
As noted in the right panel, the Sun's magnetic field almost certainly is the result of a dynamo effect, but we don't
have a good understanding of the location or nature of the dynamo. Recent data may shed some light on this
issue.
Helioseismology and Rotational Shear
As we already discussed in conjuction with helioseismology,
SOHO data indicate that the Sun rotates differentially in its outer part, but almost as a rigid body inside a
distance of about 65% of its radius (figure below). In the region just below the convection zone, from about
60-70% of the radius, there is evidence for shear (rather different rotation for adjacent latitudes). This is indicated by
the zone labeled "Shear?" in the top right figure of sound speed deviations in the Sun, also derived from SOHO data. Such
shear would be expected to help twist and wind the field lines.
Evidence from Sound Speed
The sound
speed plot lends some support to this idea. One interpretation of the slightly higher sound speed in the
proposed shear region is a lower concentration of helium than expected there based on simple models. This could result
from turbulent mixing of the matter induced by the rotation.
