Beam‐generated upper hybrid noise in Jupiter's outer magnetosphere

Abstract

Upper hybrid waves in Jupiter's outer magnetosphere are the subject of this paper which proposes a new theoretical model for their generation. Energetic electrons are assumed to be accelerated in the high‐latitude auroral zone and stream away from the planet to the outer magnetosphere. The electrons travel along magnetic field lines located at the edges of the plasma sheet through a region which has the properties of a plasma sheet boundary layer similar to the terrestrial entity. The kinematic evolution of the electron beam results in a highly collimated field‐aligned distribution which excites quasi‐perpendicular upper hybrid waves through a so‐called beam‐anisotropic heat flux instability. The instability is dominated by anomalous cyclotron harmonic resonances in a parameter regime where the gyroradius of the beam electrons is comparable to the wavelength of the wave. Propagation of the upper hybrid waves across the magnetic field into a plasma density gradient produces a spectrum of Z mode waves which then undergo a linear mode conversion to ordinary mode electromagnetic radiation. The model successfully accounts for the observations of upper hybrid noise, Z mode emissions, and continuum radiation in the Jovian magnetosphere in a self‐consistent coherent manner.