Date of Award

2021

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Engineering Physics

Department

Physical Sciences

Committee Chair

Dr. Edwin Mierkiewicz

Committee Co-Chair

Dr. Michael Chaffin

First Committee Member

Dr. Lawrence Mathew Haffner

Second Committee Member

Dr. Mathew Zettergren

Third Committee Member

Dr. Michael Hickey

Abstract

The purpose of this doctoral research dissertation is to develop a deeper understanding of the phenomenology, variability and driving processes of proton aurora at Mars. Proton aurora are the most recently discovered of the three types of Martian aurora. Due to Mars’ lack of a global dipole magnetic field, the formation processes of Martian proton aurora are uniquely different than aurora on Earth. Martian proton aurora are expected to form on the planet’s dayside via electron stripping/charge exchange processes between solar wind protons and the neutral hydrogen corona. Herein, I present the results of a study of proton aurora at Mars observed using the Imaging UltraViolet Spectrograph (IUVS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Martian proton aurora are observed in IUVS data as a prominent enhancement in the intensity of the hydrogen Lyman-alpha (Ly-α) emission (121.6 nm) between ~110-150 km altitude.

Using altitude-intensity profiles from IUVS periapsis limb scan data spanning multiple Martian years, I create a comprehensive database of proton aurora detections and characterize their phenomenology. Based on the results of this study, proton aurora are observed in ~15% of dayside periapsis profiles (with notable seasonal variability), making proton aurora the most commonly observed type of aurora at Mars. The primary factors influencing proton aurora occurrence rates are solar zenith angle (SZA) and season. The highest proton aurora occurrence rates are at low SZAs on the Mars dayside, consistent with known formation processes. Proton aurora have highest emission enhancements, peak intensities, peak altitudes, and occurrence rates (nearing 100%) around southern summer solstice. This time period corresponds with the seasonal inflation of the neutral lower atmosphere, the onset of Martian dust storm season, higher atmospheric temperatures and solar wind flux following perihelion, and seasonally increased coronal hydrogen column densities.

I compare remote sensing and in situ observations of Martian proton aurora events. By evaluating concurrent Ly-α emission enhancements and penetrating proton fluxes associated with proton aurora, it is determined that these two parameters generally track with each other, and that discrepancies between the datasets correlate with periods of high dust activity and/or extreme solar events. These discrepancies are caused by a combination of geophysical and observational factors. I also compare proton aurora detections with magnitudes and orientations of the upstream magnetic fields that control the Martian magnetic/plasma environment. I identify a possible preferential influence on Martian proton aurora activity caused by the upstream magnetic field orientations.

Numerous types of “atypical” proton aurora are examined, and the causes and variability of these events are constrained. I identify/characterize variations in proton aurora associated with local spatial and temporal variability. And though rare in the IUVS dataset, detections on the planet’s nightside are found to comprise ~4% of all proton aurora observations. The statistical properties of nightside events are quantified and possible formation mechanisms are explored.

Lastly, I coordinate a multi-model proton aurora comparison campaign: collaborating with a partnership of ~20 different modelers/scientists at nine different research institutes in the United States and around the world. Through this campaign we develop a better understanding of the physics and driving processes of Martian proton aurora, particularly emphasizing inter-model and data-model comparisons. The results of this doctoral dissertation provide a novel and unprecedented understanding of Martian proton aurora, including the short/long-term variability and primary influencing factors of these unique phenomena.

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