Speaker
Dmitry Sokoloff
(Moscow State University)
Description
We study activity waves of the kind that determine cyclic magnetic
activity of various stars, including the Sun, as a more general
physical rather than a purely astronomical problem. We try to
identify
resonances which are expected to occur when a mean-field
dynamo
excites waves of quasi-stationary magnetic field in two distinct
spherical layers. We isolate some features that can be associated
with
resonances in the profiles of energy or frequency plotted versus a
dynamo governing parameter. Rather unexpectedly however the
resonances
in spherical dynamos take a much less spectacular form than
resonances
in many more familiar branches of physics. In particular, we find
that
the magnitudes of resonant phenomena are much smaller than
seem
detectable by astronomical observations, and plausibly any
related
effects in laboratory dynamo experiments (which of course are
not in
gravitating spheres!) are also small. We discuss specific features
relevant to resonant phenomena in spherical dynamos, and find
parametric resonance to be the most pronounced type of
resonance
phenomena. Resonance conditions for these dynamo wave
resonances are
rather different from those for more conventional branches of
physics.
We suggest that the relative insignificance of the phenomenon in
this
case is because the phenomena of excitation and propagation of
the
activity waves are not well-separated from each other and this,
together with the nonlinear nature of more-or-less realistic
dynamos,
suppress the resonances and makes them much less pronounced
than
resonant effects, for example in optics.
Primary author
Dmitry Sokoloff
(Moscow State University)
Co-author
David Moss
(School of Mathematics, University of Manchester)
