Propagation of electrostatic upper-hybrid emission andZ mode waves at the geomagnetic equatorial plasmapause

A theory proposed for the generation of terrestrial myriametric radiation (nonthermal continuum) invokes the linear conversion of electrostatic upper‐hybrid emissions to escaping left‐hand polarized ordinary (L‐O) waves by virtue of propagation primarily in a plasma density gradient. The electrostatic waves first become electromagnetic Z mode waves and these subsequently escape by propagating through the radio window where the wave frequency equals the electron plasma frequency. A realistic model of the plasmapause based on spacecraft data is adopted and the electrostatic wave ray paths are computed by using Poeverlein's construction. The electromagnetic Z and L‐O rays are obtained by using a full ray‐tracing program. The accessibility of the radio window to the waves is discussed and possible inferences concerning the portion of the wave dispersion branch on which the initial instability occurs are considered.