Jovian high-latitude electron densities measured by Juno/Waves

Abstract:

The electron number density is one of the key parameters used to characterize the structure and dynamics of planetary ionospheres and an important input to many magnetospheric plasma models. One way to measure the electron density is through particle counting via plasma instruments, but it is sometimes difficult to measure the cold plasma and issues arise when dealing with spacecraft potential. Plasma wave instruments can support plasma instruments through indirect measurements of electron densities. Plasma waves have distinct frequency cutoffs and resonances that are dependent on the background plasma properties and therefore identification of these features can be used to constrain parameters such as the electron density. During times of high radiation, when the electron sensors are overwhelmed by penetrating radiation, plasma wave instruments are sometimes able to estimate the electron density, therefore aiding in the continuity of coverage. The Juno spacecraft is equipped with a plasma wave instrument, Waves, which measures the electric field from 50 Hz to 40 MHz and the magnetic field from 50 Hz to 20 kHz. We present measurements of the electron density in the Jovian high latitude regions, beginning around Io’s M-shell (6) and extending to higher M-shells. We find that identification of the lower hybrid resonance and/or the electron plasma frequency can be used to deduce the electron density for limited intervals of the spacecraft trajectory. We find the electron density ranges from approximately 800 near M-shells of 6 (Magnetic Latitude, MLat , , with km) to under 40 near M-shells of 25 (MLat , ). Here, we use M-shell in the same manner as dipole L-shell, but using the JRM09 field model with the Jovian current sheet included. During a crossing of the Io footprint tail flux tube on Perijove 12, the densities range from 8 – 40 (MLat , ). We discuss the limitations and accuracy of determining the electron density using this method and compare densities with the Jovian Auroral Distributions Experiment (JADE) over limited intervals.