Io Torus Electron Densities inward of Io's M-shell

Various characteristic frequencies observed in the plasma wave spectrum inward of Io have revealed a durable electron density profile that includes a localized relative maximum near M = 4.8 with a local minimum between this and the much greater densities closer to Io.  Scale heights relative to the centrifugal equator are of order one Jovian radius, thought to be too large for a cold heavy ion population leading to the conclusion that protons are likely responsible for the large scale height.  In this paper we show evidence of the low-frequency cutoff of the z-mode at the L=0 frequency, a polarization change at the local electron plasma frequency and low-frequency cutoff of ordinary mode waves.  The determination of the electron plasma frequency and electron cyclotron frequency from the measured magnetic field strength also allow the calculation of the upper hybrid resonance frequency and R=0 cutoff of the extraordinary mode.  Often, all of these spectral features can be found in the Juno plasma wave spectra obtained in the inner Io torus.