Catastrophic quenching in αΩ dynamos revisited
by
Axel Brandenburg(Nordita)
→
Europe/Stockholm
122:026
122:026
Description
At large magnetic Reynolds numbers, magnetic helicity evolution plays an
important role in astrophysical large-scale dynamos.
This led to the development of the dynamical alpha quenching formalism,
which predicts catastrophically low mean fields in open systems.
Here we show that in oscillatory alpha-Omega dynamos this formalism predicts an
unphysical magnetic helicity transfer between scales.
An alternative technique is proposed where this artifact is removed
by using the evolution equation for the magnetic helicity of the total
field in the shearing--advective gauge.
In the traditional dynamical alpha quenching formalism, this can be
described as an additional magnetic helicity flux of small-scale fields
that was not previously seen in homogeneous alpha^2 dynamos.
In alpha-Omega dynamos, the alternative formalism is shown to lead to larger
saturation fields than previously obtained with the traditional formalism.