Dartmouth Events

Abstract: The Earth relies on the Sun's energy, but at times this energy can be overwhelming; the Sun expels plasma which, were it not for our humble magnetic field, would erode our atmosphere (Mars, c. 4 Ga). The protective interaction Earth has with the solar wind results in spectacular auroral displays—one such auroral form is discussed in this thesis: quiet discrete auroral arcs.

Such arcs have long been studied; they are abundant, have usable symmetries, and they can predict magnetic substorms that wreak havoc in our magnetosphere. The auroral emissions, albeit beautiful, are however only the visible end of a self-consistent system of currents, electric fields, particle precipitation, and ionospheric conductivity. To study electric currents surrounding auroral arcs, it turns out, requires knowledge of all these aspects.

This thesis enhances our understanding of auroral arcs through the lens of ionospheric current closure. The ionosphere has its plasma transition to being collisional with the neutrals over only about 100 km altitude, which allows for currents to flow perpendicular to the local magnetic field—something they cannot do outside our ionosphere. This couples the ionosphere and magnetosphere through magnetic-field-aligned current closure, where the ionosphere can present load characteristics not unlike those in a circuit resistor.

The discrete auroral arcs come into play because they are the result of attempting to host field-aligned currents through magnetic flux tubes that can be too tenuous to fulfill their amperage without the creation of parallel electric fields. Such fields can cause electrons to accelerate to energies high enough to ionize the atmosphere which enhances the ionospheric conductivity, affecting the pathways for current closure.

This thesis outlines the methodology and use of a plethora of heterogeneous, multi-platform auroral measurements curated for driving fully-three-dimensional ionospheric simulations of auroral arcs. This filters for solutions that are geophysical and self-consistent, and allows for the investigation of sensitivities to various input parameters. This work highlights, not just various considerations in performing such simulations, but the very fact that they require all three dimensions for a complete picture. After all, the equations that govern auroral arc systems are inherently three-dimensional in nature.

Graduate Advisor: Professor Kristina Lynch

Join Zoom Meeting
https://dartmouth.zoom.us/j/92105366260?pwd=vb06sLMg7Ikt5sfAa1sUfc0ZDSlSsR.1

Meeting ID: 921 0536 6260
Email Physics.Department@dartmouth.edu for passcode