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    Modelling Electrodynamics in Saturn's Upper Atmosphere

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    Author
    Vriesema, Jess William
    Issue Date
    2020
    Keywords
    Dynamics
    Electrodynamics
    Ionosphere
    Planetary science
    Saturn
    Thermosphere
    Advisor
    Yelle, Roger V.
    
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    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Although electrodynamics plays an important role in controlling Saturn's thermospheric circulation and energy balance at high latitudes, less is known about its effects at lower latitudes. Recent observations from the Cassini magnetometer instrument near the equator during the Grand Finale tour revealed azimuthal magnetic field perturbations associated with ionospheric electrodynamics at low latitudes. If a significant ionospheric wind dynamo exists in Saturn's ionosphere at low and middle latitudes, it could alter the circulation and energy balance of Saturn's upper atmosphere and could explain the magnetic field perturbations at low latitudes. In this manuscript, we develop several models of thermospheric electrodynamics, including a new formulation for coupling the ionosphere and magnetosphere, and use them to investigate the role ion drag and resistive heating throughout Saturn's thermosphere. Results from our models suggest that electrodynamics can generate substantial currents at low and middle latitudes that can in some cases be comparable to high-latitude currents. We find that the electrodynamics is strongly dependent on the conductivity and wind profiles. In particular, the presence of an equatorial jet is important for driving significant eastward magnetic field perturbations and electrodynamics at low latitudes. Ion drag can help lift an equatorial jet from below to higher altitudes than it could otherwise reach, and may be able to spread a narrow equatorial jet in latitude as well. Because ion drag reduces wind shears that drive electrodynamics, any evidence of significant electrodynamics implies that the winds experience continual forcing by other mechanisms. In some models, ion drag partially opposes the Coriolis force at middle latitudes, slightly weakening the Coriolis barrier and allowing some meridional transport of auroral energy. The resistive heating predicted by our models is insufficient to explain the surprisingly high temperatures at low latitudes. Finally, we discuss directions for future research.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Planetary Sciences
    Degree Grantor
    University of Arizona
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