Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Alfv\'en-dynamo balance and magnetic excess in MHD turbulence   3D Magnetohydrodynamic (MHD) turbulent flows with initially magnetic and
kinetic energies at equipartition spontaneously develop a magnetic excess (or
residual energy), as well in numerical simulations and in the solar wind.
Closure equations obtained in 1983 describe the residual spectrum as being
produced by a dynamo source proportional to the total energy spectrum, balanced
by a linear Alfv\'en damping term. A good agreement was found in 2005 with
incompressible simulations; however, recent solar wind measurements disagree
with these results. The previous dynamo-Alfv\'en theory is generalized to a
family of models, leading to simple relations between residual and total energy
spectra. We want to assess these models in detail against MHD simulations and
solar wind data. The family of models is tested against compressible decaying
MHD simulations with low Mach number, low cross-helicity, zero mean magnetic
field, without or with expansion terms (EBM or expanding box model). A single
dynamo-Alfv\'en model is found to describe correctly both solar wind scalings
and compressible simulations without or with expansion. It is equivalent to the
1983-2005 closure equation but with critical balance of nonlinear turnover and
linear Alfv\'en times, while the dynamo source term remains unchanged. The
discrepancy with previous incompressible simulations is elucidated. The model
predicts a linear relation between the spectral slopes of total and residual
energies $m_R = -1/2 + 3/2 m_T$. Examining the solar wind data as in
\cite{2013ApJ...770..125C}, our relation is found to be valid whatever the
cross-helicity, even better so at high cross-helicity, with the total energy
slope varying from $1.7$ to $1.55$.

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The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
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The categories of this paper are: eess
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
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The categories of this paper are: q-fin
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The categories of this paper are: econ
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat