Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. An upper hybrid oscillation is a mode of oscillation of a magnetized plasma. It consists of a longitudinal motion of the electrons perpendicular to the magnetic field with the dispersion relation omega^2 = omega_{pe}^2 + omega_{ce}^2 + 3 k^2 v_{mathrm{e,th}}^2, where (in cgs units) pe = (4 nee2 / me)1 / 2 is the electron plasma frequency, and ce = eB / mec is the electron cyclotron frequency. This oscillation is closely related to the plasma oscillation found in unmagnetized plasmas or parallel to the magnetic field, where the pe term arises from the electrostatic restoring force and the 3k²ve,th² term arises from the restoring force of electron pressure.