Superthermal electrons and Bernstein waves in Jupiter's inner magnetosphere

Abstract

A theoretical model for generation of banded electrostatic emissions by low density, superthermal electrons is developed for application to Jupiter's magnetosphere. The model employs a power law form for the energy dependence and a loss cone pitch angle distribution of the superthermals to drive convective instability of Bernstein modes. We concentrate on instability in the upper hybrid band and on lower harmonic bands below the upper hybrid frequency. A direct correspondence between spectral features of the 3/2's band and resonant superthermal electrons is found. The concept of a critical flux j⊥* of resonant electrons able to provide 10 e‐foldings of electric field amplification yields an explicit relation j⊥* ∼p in terms of the background thermal electron pressure. This result is used to construct a theoretical/empirical model of thermal electron density and temperature from 6–20 RJ in the Jovian magnetosphere which suggests that the ion and electron temperatures satisfy Te <Ti ∼10Te in this region. Finally, wave ray paths are computed for propagation in the magnetic equator and in the magnetic meridional plane of a dipole magnetic field. These ray paths suggest that intense wave activity is tightly confined to a small latitudinal extent, Λ≲±4°, about the magnetic equator.