Quasilinear Analysis in the Source Region of Jovian Hectometric Emission Associated With Upward Electron Beams

Abstract

Intense upward electron beams were measured by the Juno JADE instrument in the northern hemisphere, low-latitude auroral zone source region. In this study we report on how these electron beams interact with plasma near and within the Jovian hectometric (HOM) emission (1 MHz 5 MHz) source region. Within the source region large upward loss cones are observed in the northern polar region at radial distances of $\sim$ 2Rj, magnetic latitude of $\sim 70°$. Intense, narrow electron beams ( 3 keV) are then observed, but within one second wave-particle scattering is observed, filling the loss cone to energies $>$50 keV. These energies persist for several seconds before fading, leaving an empty loss cone again. The loss cone provides a free-energy source for HOM emission resulting from the cyclotron maser instability. We use quasilinear analysis to examine the generation of HOM and the dynamics of wave-particle interaction of the electron beams with HOM, and the generation via Landau interaction of whistler mode emission. The dynamic spectrum of the HOM emission generated by the loss-cone electrons as well as that of the low-frequency whistler-mode waves generated by the up-going electron beam can be constructed by quasilinear theory, which compare well with observation. The saturated state of the energetic electron velocity distribution function constructed via quasilinear theory also compare reasonably with observation.