Dissertation
The implications and characteristics of diffuse-like but dynamic aurora
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2023
DOI: 10.25820/etd.007178
Abstract
The aurora (northern/southern lights) are a majestic display of light that illuminates the night sky at high latitudes in the northern and southern hemispheres. These lights come in several different varieties. Discrete and substorm aurora are the brightest and most photogenic type, but in this thesis we focus on the dimmer, but just as important, diffuse aurora. More specifically, we look at subsets of diffuse aurora that are also dynamic. A majority of this work is devoted to pulsating aurora, which appear as an uncoordinatedsymphony of dim auroral patches that blink on and off across wide portions of the sky. Pulsating aurora plays an important role in energy transfer between the magnetosphere and the upper atmosphere. This energy transfer can have significant impacts on the atmosphere, such as ozone depletion. Using electron density measurements from the Poker Flat Incoherent Scatter Radar, we were able to statistically quantify the energy flux of electrons responsible for pulsating aurora. We found a significant contribution from > 30 keV electrons, which increases in close temporal proximity to a substorm and for periods of high AE index. We also found that following a substorm, the energy flux from > 30 keV electrons decays with an e-folding time of 0.95 hr. Using wave measurements from the Van Allen Probes, we were able to connect this timescale to a similar e-folding time of 1.18 hr for lower-band chorus waves following a substorm. Combined, these results support the hypothesis that pulsating aurora represents a significant loss of energetic electrons from the outer radiation belt to the atmosphere. It also supports the hypothesis that pulsating aurora are the result of Doppler-shifted cyclotron resonance between energetic substorm electrons and lower-band chorus waves. However, much regarding diffuse and dynamic aurora is still unknown. This is evident in the diffuse auroral eraser, a new phenomenon that we characterize as a rapid brightening and then dimming of a diffuse arc superimposed on a background diffuse aurora. Upon dimming, the background aurora get erased and takes approximately 20 seconds to return to normal. We believe this feature may shed light on how different magnetospheric waves could influence each other. However, we need more observations to solve this puzzle and hope our results will inspire future studies into diffuse and dynamic aurora.
Details
- Title: Subtitle
- The implications and characteristics of diffuse-like but dynamic aurora
- Creators
- Riley Troyer
- Contributors
- Allison N. Jaynes (Advisor)Casey T. DeRoo (Committee Member)Jasper S. Halekas (Committee Member)David M. Miles (Committee Member)Robert G. Michell (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Spring 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007178
- Number of pages
- xviii, 144 pages
- Copyright
- Copyright 2023 Riley Troyer
- Language
- English
- Date submitted
- 04/24/2023
- Date approved
- 05/05/2023
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 97-115).
- Public Abstract (ETD)
The aurora (northern/southern lights) are a majestic display of light that illuminates the night sky at high latitudes in the northern and southern hemispheres. These lights come in several different varieties. Discrete and substorm aurora are the brightest and most photogenic type, but in this thesis we focus on the dimmer, but just as important, diffuse aurora. More specifically, we look at subsets of diffuse aurora that are also dynamic. A majority of this work is devoted to pulsating aurora, which appear as an uncoordinated symphony of dim auroral patches that blink on and off across wide portions of the sky. Pulsating aurora are caused when energetic electrons get perturbed into the atmosphere from a region of Earth’s magnetic field called the Van Allen radiation belts. These aurora are important to study because they can impact a variety of processes important to society, such as destroying ozone. In this thesis, we studied the energy of pulsating aurora electrons. We quantified the most energetic events and found that they occur close in time to a shock in Earth’s magnetic field, called a substorm. We also found that the total energy reduced, after a substorm, over a specific time frame. We were then able to connect that time frame to a similar one that we measured, using satellites, for electromagnetic waves in the Van Allen radiation belts. This supports the hypothesis that pulsating aurora originate in the Van Allen radiation belts and that the electrons which cause them are perturbed into the atmosphere by waves in Earth’s magnetic field. However, much regarding diffuse and dynamic aurora is still unknown. This is evident in the diffuse auroral eraser, a new phenomenon that we characterize in this thesis. We believe this feature may shed light on how different types of waves in Earth’s magnetic field could influence each other. However, we need more observations to solve this puzzle and hope our results will inspire future studies into diffuse and dynamic aurora.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984437259202771
Metrics
5 File views/ downloads
18 Record Views