Mémoire

Abstract

This thesis presents a statistical study of auroral signatures associated with particle injections at Jupiter. Auroral injections are events where populations of energetic particles are rapidly accelerated and injected into Jupiter’s magnetosphere. The signature of these injections manifest as compact auroral structures, reflecting lo calized increases in high-energy particle populations that move azimuthally around the planet, guided by magnetic field gradients and curvature. They can exhibit a longitudinal shift between the brightness peak and the color ratio peak. This shift is defined as negative when higher-energy particles begin their differential drift relative to lower-energy particles, producing an offset downstream in the direction of plasma rotation around the planet. In her thesis, Dumont (2023) reported a surprisingly high number of positive shifts that were difficult to explain physically; these results were likely influenced by limitations in the auroral image reconstruction technique. In this thesis, an improved map reconstruction method is developped, specifically designed to reduce such artifacts, providing a more accurate representation of par ticle injections and their associated shifts. Using ultraviolet spectral data collected by the Ultraviolet Spectrograph (UVS) instrument aboard the Juno spacecraft, a comprehensive analysis was performed on 693 injection events to characterize the spatial and temporal relationships between auroral features. Auroral injections are mapped to Jupiter’s equatorial plane using the JRM33magnetic field model. For each event, intensity profiles of both brightness and color ratio are extracted along arcs crossing the injection coordinates. The intensities are measured on brightness and color ratio maps, reconstructed from successive observation ribbons acquired by Juno. Light curves are then constructed, and the longitudinal shift between the brightness and color ratio peaks is measured. A statistical analysis of these shifts, as well as of event occurrence, is performed as a function of longitude, local time, radial distance, and hemisphere. The analysis reveals clear hemispheric asymmetries in Jupiter’s auroral dynamics. Small-scale structures dominate overall. In the Northern Hemisphere, fewer struc tures are detected between 135°–180° longitude. In the Southern Hemisphere, struc ture occurrences increase between 12:00 and 03:00 LT, whereas in the north this increase occurs later. Positive longitudinal shifts between brightness and color ratio peaks are rare, in contrast with earlier studies. Observed negative and no-shifts are consistent with energy-dependent particle dynamics: populations remain together for no-shifts, while higher-energy particles start drifting for negative shifts. These results suggest that previous reports of frequent positive shifts were influenced by methodological biases, and they highlight the combined role of magnetic field asym metries and dynamic plasma processes in shaping auroral variability