Salveter, Annika Pia ORCID: 0000-0003-1030-8431
(2024).
Statistical Classification of Jupiter’s Aurora - A joint analysis of complementary Juno observations.
PhD thesis, Universität zu Köln.
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Abstract
Jupiter’s aurora is the most powerful in our solar system and challenges our understanding due to its variable shape and intensities. The Jupiter magnetosphere, influenced by rapid rotation, a strong magnetic field, and Io’s mass load, was studied extensively by the Juno mission, which arrived in 2016. Juno’s observations of the auroral region, especially its low-altitude polar crossings, revealed diverse phenomena, questioning existing knowledge. The hypothesis that powerful wave-particle interactions cause auroral acceleration is gaining increasing attention while raising questions about the initial assumption that static electron potentials are responsible for intense emission. Measurements supporting this hypothesis are rarely seen, making it difficult to compare them with the auroral features we observe on Earth. This study aims to explore acceleration theories driving Jupiter’s auroras by calculating electron distribution occurrence rates and studying their connection with magnetic field changes and ultraviolet emissions, which is essential for understanding the auroras. Therefore, we combine data from 20 flybys, offering a global perspective by statistically comparing the perijoves observations, rather than focusing on individual local observations. The approach of this is to connect associated various instrument data, combining magnetic fields, electron intensities, and UV emissions, to better understand the electron acceleration mechanisms and processes that generate the intense auroral features. This study found a link between the intense auroras on Jupiter and broadband broad electron energy distributions and azimuthal magnetic field deviations of several 100 nT, indicating field-aligned currents. Thus, stochastic processes might predominantly accelerate intense electron beams, occasionally involving electrostatic structures. Upward and downward beams aligned with the associated currents and bidirectional distributions in downward current regions are observed. Bidirectional electron distributions in downward current regions contradict electrostatic currents, providing adequate intensities for intense auroras. The electron beams display broadband energy distributions through energies from 30-1000 keV, contributing to 93% of auroral emissions, highlighting the importance of stochastic processes. Significant magnetic field fluctuations of 100 nT were observed when the diffuse aurora was present at lower magnetic latitudes (< 76°). Despite magnetometer limitations at low altitudes, observations at up to 8 RJ revealed minor magnetic field fluctuations of a few nT occurring in one-second intervals during main emission crossings. Thus, minor magnetic field changes on periods shorter than a few seconds may indicate the acceleration of auroral electrons due to the interactions with related waves. Examining various plasma characteristics revealed that electrostatic current and wave-particle interaction contribute significantly to intense auroral arcs on Jupiter. Wave-particle interactions are especially prominent. The coexistence of these accelerations underscores Jupiter’s magnetospheric variability. Enhancing this analysis in spatial and temporal coverage by the Juno data and using the full range of Juno instruments would be valuable. Comparing plasma properties on a global scale is beneficial in uncovering the complex interaction of the various acceleration mechanisms to understand the most dazzling auroral phenomena observed in the solar system, the Jovian aurora.
Item Type: | Thesis (PhD thesis) | ||||||||||
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URN: | urn:nbn:de:hbz:38-740962 | ||||||||||
Date: | 28 October 2024 | ||||||||||
Language: | English | ||||||||||
Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||||
Divisions: | Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology | ||||||||||
Subjects: | Physics Earth sciences |
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Date of oral exam: | 19 January 2024 | ||||||||||
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Refereed: | Yes | ||||||||||
URI: | http://kups.ub.uni-koeln.de/id/eprint/74096 |
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