Speaker
Jörn Warnecke
(Max-Planck-Institut für Sonnesystemforschung)
Description
Sunspots occurring on the solar surface following a typical
pattern during the activity cycle. At the beginning of the
cycle they appear at high latitude, whereas at the end they
appear close to the equator. This is associated with an
underlying strong toroidal field which migrates equatorward.
Since a few years this behavior has been reproduced in
global convective dynamo simulations. I will present results
from our simulations of global convective dynamos. All of
these simulations produce cyclic and migrating mean magnetic
fields. Through detailed comparisons, we show that the
migration direction can be clearly explained by an
alpha-Omega dynamo wave following the Parker-Yoshimura rule.
This lead to the conclusion, that the equatorward migration
in this and other work is due to a positive (negative)
alpha-effect in the northern (southern) hemisphere and a
negative radial gradient of rotation outside the inner
tangent cylinder of these models. This idea is supported by
a strong correlation between negative radial shear and
toroidal field strength in the region of equatorward
propagation. In the Sun the only region, where the rotation
rate possesses a negative radial gradient, is in the
near-surface shear layer. A positive alpha-effect there
would lead to an equatorward propagating dynamo wave.
Furthermore, I will present results of combined simulation
of solar dynamo and a coronal envelope. These simulation
give us indication, that the latitudinal temperature
variation play an important role in generating the
differential rotation profile of the Sun through turbulent
Reynold stresses. I will show, that the meridional component
of the Reynolds stress can explain the formation of a
near-surface shear layer in the Sun.
Primary author
Jörn Warnecke
(Max-Planck-Institut für Sonnesystemforschung)
