= Magnetoelastic wave in an isotropic magnetic tangle
{title2=$\omega^2=\langle B^2\rangle k^2/3$}
= Magnetoelastic waves in an isotropic magnetic tangle
{synonym}
A long-wavelength transverse disturbance of an initially isotropic <magnetic second-moment tensor> behaves as an elastic shear <wave> when small-scale rearrangements of the tangle are omitted. For $v_A^2=\langle B^2\rangle/3$, its <fluid displacement> obeys $\partial_t^2\boldsymbol\xi=v_A^2\nabla^2\boldsymbol\xi$ and $\nabla\cdot\boldsymbol\xi=0$ on the oscillatory branch. The tensor perturbation is $\delta M_{ij}=v_A^2(\partial_i\xi_j+\partial_j\xi_i)$. A zero mean <magnetic field> does not imply zero restoring <magnetic tension>.
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