Dissertation
Whistler-mode waves and the acceleration of energetic electrons in the Jovian polar region: observations from the Juno spacecraft
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2020
DOI: 10.17077/etd.005613
Abstract
Whistler-mode auroral hiss is one of the strongest, naturally occurring electromagnetic wave emissions that exists in the high latitude regions of planetary magnetospheres. Although this class of emissions has been studied for nearly 60 years, most of our understanding of the underlying physics has been based on observations from Earth. Although terrestrial theories, developed from a plethora of observations, have helped with our understanding of the underlying physics of auroral hiss and its association with electrons, these theories are yet to be tested in diverse environments, like Jupiter. Jupiter is the ideal laboratory for understanding fundamental plasma physics processes because Jupiter’s aurora is the most powerful in the solar system and because Jupiter’s polar regions are the hot spots of wave-particle interactions and auroral activity.
Juno is the first mission to pass directly over the low altitude polar and auroral regions of Jupiter, making observations in regions where particle acceleration is abundant and radio and plasma wave emissions are generated. The Juno spacecraft observed intense broadband upward-propagating whistler-mode waves associated with upward-traveling energetic electrons over the entire Jovian polar region. Whistler-mode auroral hiss is known to be generated by electron energy beams via an instability at the Landau resonance. We discuss the mechanisms by which the waves are produced and interact with the electrons by changing their energy and pitch angle. The interaction begins with a downward field-aligned current over the polar cap, generating strong downward parallel electric fields and upward-traveling electron beams. The beams then produce broadband upward-traveling whistler-mode auroral hiss by a beam-plasma instability at the Landau resonance. As the waves propagate upwards, their phase velocity increases, which has the potential to carry trapped electrons to high energies. We show evidence that they participate in pitch angle scattering and acceleration of resonant electrons, causing the electrons to deviate from the first adiabatic invariant motion, which otherwise would cause their pitch angle to decrease. We also present numerical calculations of wave growth rates and show that they are sufficient to produce the observed wave intensities. This study brings a new understanding of fundamental physics processes that are common to all planetary systems with strong magnetic fields. Specifically, wave-particle interaction is key to understanding the underlying microphysics that drives the powerful and dynamic emissions in the polar regions of Jupiter.
Details
- Title: Subtitle
- Whistler-mode waves and the acceleration of energetic electrons in the Jovian polar region: observations from the Juno spacecraft
- Creators
- Sadie Suzanne Elliott
- Contributors
- Jasper S Halekas (Advisor)Donald A Gurnett (Committee Member)Allison N Jaynes (Committee Member)Cornelia C Lang (Committee Member)Wen Li (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Summer 2020
- DOI
- 10.17077/etd.005613
- Publisher
- University of Iowa
- Number of pages
- xiv, 117 pages
- Copyright
- Copyright 2020 Sadie Suzanne Elliott
- Language
- English
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (page 100-110).
- Public Abstract (ETD)
Explaining how waves are generated and how particles are accelerated is key to understanding the microphysics that drive powerful and dynamical auroras. Jupiter is an excellent laboratory for testing auroral theories because its auroral emissions are the most powerful in the solar system and the polar regions are extremely under-explored. The Juno mission is the first spacecraft to pass over the low altitude polar regions of Jupiter and observe waves and particles. This thesis work focuses on one particularly prominent wave emission called whistler-mode auroral hiss. This emission is found to correlate with energetic electrons and interact with them in various ways, possibly explaining Jupiter’s auroral emissions. This thesis work will help plan future spacecraft missions to giant planets and aid in filling in the missing information regarding the main drivers of Jupiter’s aurora.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9983988298102771
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