Jupiter Long Dispersion Lightning Whistlers that propagate through the Io torus: Juno Observations

Abstract

The detection of lightning whistlers in planetary magnetospheres can provide valuable information about the properties of both the source lightning, and the plasma environment along the whistler propagation path. The Juno spacecraft, with its multiple polar orbits, is providing a new opportunity to examine the properties of lightning and lightning whistlers at Jupiter, and to investigate the density characteristics of the plasma the whistlers propagate through. Juno Waves has detected thousands of lightning whistlers below 20 kHz with dispersive curve time scales of a few to 10s of ms (dispersion constants D < 2 sec Hz^(1/2)). The small dispersion constants suggest a short propagation path from the lightning source to the spacecraft (lightning located directly below the spacecraft), which has been verified from wave propagation direction analysis. During some orbits, Juno Waves has also detected lightning whistlers exhibiting longer dispersion times of a few seconds (D > 500 sec Hz^(1/2)), similar to the whistlers detected by the Voyager spacecraft during its flyby of Jupiter. These longer dispersion whistlers are detected when Juno is located on magnetic field lines that map back to the equator near the orbit of Io. Initial analysis of these whistlers finds that D can sometimes vary by a factor of 2 in a short period of time, suggesting large variation in the plasma density on adjacent field lines. Observations of these longer dispersion whistlers are presented and the conditions under which these emissions are detected, the properties of the emissions, and the role the Io torus plays to produce the observed spectral characteristics of these longer dispersion whistlers discussed.