Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Systematic parameter study of dynamo bifurcations in geodynamo
  simulations   We investigate the nature of the dynamo bifurcation in a configuration
applicable to the Earth's liquid outer core. Numerical studies on the stability
domain of dipolar magnetic fields found a dichotomy between non-reversing
dipole-dominated dynamos and the reversing non-dipole-dominated multipolar
solutions. We show that, by considering weak initial fields, the above
transition disappears and is replaced by a region of bistability. Such a result
was also observed in models with free-slip boundaries in which the geostrophic
zonal flow can develop and participate to the dynamo mechanism for non-dipolar
fields. We show that a similar process develops in no-slip models when viscous
effects are reduced sufficiently.
  The following three regimes are distinguished: (i) Close to the onset of
convection ($Ra_c$) with only the most critical convective mode (wave number)
being present, dynamos set in supercritically and are dipole-dominated. (ii) in
the range $3<Ra/Ra_c<Ra_c$, the bifurcations are subcritical and only
dipole-dominated dynamos exist. (iii) $(Ra/Ra_c>10)$, the relative importance
of zonal flows increases with $Ra$ in non-magnetic models. The field topology
depends on the magnitude of the initial magnetic field. The dipolar branch has
a subcritical behavior whereas the multipolar branch has a supercritical
behavior. By approaching more realistic parameters, the extension of this
bistable regime increases. A hysteretic behavior questions the common
interpretation for geomagnetic reversals.
  Far above the dynamo threshold (by increasing the magnetic Prandtl number),
Lorentz forces contribute to the first order force balance, as predicted for
planetary dynamos. When $Ra$ is sufficiently high, dipolar fields affect
significantly the flow speed, the flow structure and heat transfer which is
reduced by the Lorentz force regardless of the field strength.

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The categories of this paper are: plasm-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ph
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The categories of this paper are: cs
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: eess
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The categories of this paper are: chem-ph
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The categories of this paper are: mtrl-th