= Magnetohydrodynamic wave polarization
{title2=$\mathbf u'=U\widehat{\mathbf e}$}
= MHD wave polarization
{c}
{synonym}
A polarization specifies the direction or trajectory of the oscillating <velocity> and <magnetic field> in a <magnetohydrodynamic wave>. The linear <Alfvén wave> has velocity perpendicular to the plane of the background <magnetic field> and <wavevector>; the <magnetosonic waves> have velocity in that plane. A real fixed polarization vector gives a linear oscillation. Two orthogonal components of equal amplitude in quadrature give a circular trajectory. For propagation parallel to a uniform field, combining the two degenerate transverse linear polarizations produces circular polarization; at finite amplitude its constant transverse magnetic-field magnitude removes the longitudinal <magnetic pressure> gradient.
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