J. O. Stenflo, A. G. Kosovichev
The magnetic flux that is generated by dynamo inside the Sun emerges in the
form of bipolar magnetic regions. We have analyzed the whole set of solar
magnetograms obtained with the SOHO/MDI instrument in 1995-2011, and
automatically identified 160,079 bipolar magnetic regions that span a range of
scale sizes across nearly four orders of magnitude. Their properties have been
statistically analyzed, in particular with respect to the polarity orientations
of the bipolar regions, including their tilt angle distributions. The latitude
variation of the average tilt angles (with respect to the E-W direction), known
as Joy's law, is found to closely follow the relation 32.1*sin(latitude)[deg].
There is no indication of a dependence on region size that one may expect if
the tilts were produced by the Coriolis force during the buoyant rise of flux
loops from the tachocline region. A few percent of all regions have
orientations that violate Hale's polarity law. We show examples, from different
phases of the solar cycle, where well defined medium-size bipolar regions with
opposite polarity orientations occur side by side in the same latitude zone.
Such oppositely oriented large bipolar regions cannot be part of the same
toroidal flux system, but different flux systems must coexist in the same
latitude zones. These examples are incompatible with the paradigm of coherent,
subsurface toroidal flux ropes as the source of sunspots, and instead show that
fluctuations must play a major role at all scales for the turbulent dynamo. We
see no observational support for a separation of scales or a division between a
global and a local dynamo, since also the smallest scales in the data set
retain a non-random component that significantly contributes to the accumulated
emergence of a N-S dipole moment that leads to the replacement of the old
global poloidal field with a new one that has the opposite orientation.
View original:
http://arxiv.org/abs/1112.5226
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