Magnetosonic wave

A magnetosonic wave is a longitudinal wave^[1] of ions (and electrons) in a magnetized plasma propagating perpendicular to the stationary magnetic field. The wave is dispersionless with a phase velocity ω/k given by

$\frac{\omega^2}{k^2}=c^2\,\frac{v_s^2+v_A^2}{c^2+v_A^2}$ ,