Wave driven diffuse aurora and ionospheric conductance global patterns

Abstract

Auroral precipitation is the second major energy source after solar irradiation that ionizes the Earth’s upper atmosphere. In this study we define 3 types of auroral activity as broadband, monoenergetic, and diffuse aurora. Diffuse aurora from electron precipitation, or diffuse electron aurora, contributes over 60% of the total auroral energy flux. Through constant collisions between the electrons and neutral particles in the atmosphere the electron flux ionizes the atmosphere and strongly contributes to the ionospheric conductance. The ionization, electron energy flux, and conductance play a significant role in defining the ionosphere-thermosphere dynamics. One major contributor to the precipitation of these electrons in the inner- magnetosphere is wave-particle interactions. By resonating with the electron gyrofrequency of electrons in space, specific plasma waves can change the particle energy and cause precipitation into the Earth’s atmosphere. Chorus banded waves and Electron Cyclotron Harmonic waves (ECH) are major contributors to electron precipitation because of their occurrence and wave frequency. The propagation of these waves and the influx of electron population in the inner magnetosphere has a strong dependency on geomagnetic activity. This dissertation quantifies the impact of Chorus and ECH waves on diffuse electron aurora and ionospheric conductance during quiet, medium, and strong geomagnetic activities. Using observations from the Timed History Events and Macroscale Interactions during Substorms (THEMIS) satellite probes we produce a statistical baseline for the electron flux rates, wave amplitude and observation statistics, and inner-magnetosphere conditions such as electron temperatures and densities. We directly derive the energy flux spectrum of diffuse electron precipitation using quasi-linear theory with these observations as initial conditions. We then calculate the height-integrated conductance from the wave-driven aurora spectrum using an electron impact ionization model to determine the rate of ionization and the US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar (NRLMSISE-00) model from the 2000s for neutral atmosphere components. By utilizing Fang’s (2010) ionization model, NRLMSISE-00 for the neutral atmosphere components, and the University of California, Los Angeles (UCLA) Full Diffusion Code, we improve upon the standard generalization of Maxwellian diffuse electron precipitation patterns and ionosphere conductance statistics. Our study of global auroral precipitation and ionospheric conductance from both Chorus and ECH wave statistics allows us to quantify, for the first time, the relative contributions of these two waves. We show that the total electron flux and conductance pattern from our results agree with those of the Ovation Prime model over the pre-midnight to post­ dawn sector as geomagnetic activity increases. Our study examines the relative contributions of Upper Band Chorus (UBC) and Lower Band Chorus wave (LBC) driven conductance in the ionosphere. We found LBC waves drove diffuse electron precipitation significantly more than UBC waves, and that their combined precipitation and conductance was greater than the impact of ECH waves by 30% for high activity and upwards of 70% more for low geomagnetic activity.