A magnetosonic wave (also magnetoacoustic wave) is a longitudinal wave 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
where vs is the speed of the ion acoustic wave, vA is the speed of the Alfvén wave, and c is the speed of light in vacuum.
![\frac{\omega^2}{k^2}=\frac12(v_s^2+v_A^2)\bigg[1\pm\sqrt{1 - \frac{4v_s^2v_A^2\cos^2\theta}{(v_s^2+v_A^2)^2}}\bigg]](/Images/godic/202501/25/0e10a0321ca951fd157faabba663a4f71929.png")