Saturn chorus latitudinal variations

Abstract

The variation of propagation properties of whistler mode chorus as a function of latitude is not well known at Saturn but is important for the calculation of pitch angle diffusion and nonlinear growth of chorus. The Cassini spacecraft has spent a portion of its orbital time in high-inclination orbits, allowing traversal of the magnetic equator at nearly constant L shell for several passes. This is important since chorus is believed to propagate dominantly close to the magnetic field direction. We have investigated the change of wave normal angle, whistler mode magnetic intensity, and ambient magnetic field inhomogeneity as a function of latitude observed by the Radio and Plasma Wave investigation onboard the Cassini instrument. We find that wave normal angles along a nearly constant L shell remain close to field-aligned, except nearest the equator, and whistler mode wave intensity increases from the magnetic equator, according to a power law. The ambient magnetic field shows an inhomogeneity that is lower than Earth's, but there is a lack of drifting-frequency signatures nearest the equator. The bandwidth of the chorus emission can be described by a simple exponential. The bandwidth increases from the equator, peaking a few degrees away in a region of strong nonlinear growth and then decreases at higher latitudes.

Survey analysis of chorus intensity at Saturn

“…At Saturn, the most intense emission does not occur at the magnetic equator, as at Earth, but a few degrees away from the equator, where nonlinear growth is observed [cf. Menietti et al ., ]. At Earth, the upper band chorus is much weaker than the lower band [ Meredith et al ., ]; however, at Saturn, that is not the case as we have found (Figure ).…”

“…Menietti et al . [] have reported on latitudinal variations of Saturn chorus for the special case of Cassini orbits along nearly constant L shells near the magnetic equator. The second region of chorus observations reported by Hospodarsky et al .…”