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

TL;DR

This study uses Juno observations to analyze ultraviolet aurora injection signatures on Jupiter, finding scattering as the main cause and identifying two types of injections with arc features possibly resulting from electron drift.

Contribution

It introduces an automatic detection method for aurora features and clarifies the roles of scattering and injection types in Jupiter's magnetosphere.

Findings

Scattering likely explains most electron precipitation in injections.

Injection signatures can be classified into dawn-storm and non-dawn-storm types.

Arc features may result from energy-dependent electron drift of injection signatures.

Abstract

Discrete features in Jupiter's ultraviolet aurora have been interpreted as signatures of plasma injections in the middle magnetosphere. There exists some ambiguity whether magnetodisc scattering or high-latitude Alfvenic acceleration best describes the observed properties of these injection signatures, and also to what extent arcs in the outer emission are related to injections. Many injection signatures are the result of the evolution of dawn storms; there is, however, 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: dawn-storm 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.