Characterising injection signatures in Jupiter’s ultraviolet aurora using Juno observations

Discrete features in Jupiter’s ultraviolet aurora have been interpreted as signatures of plasma injections in the middle magnetosphere. There exists some ambiguity as to whether magnetodisc scattering or high-latitude Alfvénic acceleration best describes the observed properties of these injection signatures, and also the extent to which extent arcs in the outer emission are related to injections. Many injection signatures are the result of the evolution of dawn storms; however, there is limited evidence that non-dawn-storm injection signatures are sometimes present in the aurora. We use automatic detection of these discrete features, alongside data from Juno-UVS and in situ measurements by other Juno instruments, to show that scattering likely accounts for most of the electron precipitation associated with injection signatures. Additionally, there is evidence that injection signatures can be classified into two types: dawnstorm and non-dawn-storm. Arc-like features in the outer emission show very similar properties to traditional blob-like injection signatures and may consist of sequences of injection signatures that have broadened into an arc via energy-dependent electron drift.