  Observations show that the photospheric solar magnetic dipole usually does
not vanish during the reversal of the solar magnetic field, which occurs in
each solar cycle. In contrast, mean-field solar dynamo models predict that the
dipole field does become zero. In a recent paper Moss et al. (2013) suggested
that this contradiction can be explained as a large-scale manifestation of
small-scale magnetic fluctuations of the surface poloidal field. Here we
compare this interpretation with WSO (Wilcox Solar Observatory) photospheric
magnetic field data in order to determine the amplitude of magnetic
fluctuations required to explain the phenomenon and to compare the results with
predictions from a simple dynamo model which takes these fluctuations into
account. We demonstrate that the WSO data concerning the magnetic dipole
reversals are very similar to the predictions of our very simple solar dynamo
model, which includes both mean magnetic field and fluctuations. The ratio
between the rms value of the magnetic fluctuations and the mean field is
estimated to be about 2, in reasonable agreement with estimates from sunspot
data. The reversal epoch, during which the fluctuating contribution to the
dipole is larger than that from the mean field, is about 4 months. The memory
time of the fluctuations is about 2 months. Observations demonstrate that the
rms of the magnetic fluctuations is strongly modulated by the phase of the
solar cycle. This gives additional support to the concept that the solar
magnetic field is generated by a single dynamo mechanism rather than also by
independent small-scale dynamo action. A suggestion of a weak nonaxsymmetric
magnetic field of a fluctuating nature arises from the analysis, with a
lifetime of about 1 year.

Solar and Stellar Astrophysics