Sources of Auroral Precipitation: Balance, Impacts & Drivers

Abstract

Auroral precipitation in Earth's polar regions is a product of the solar wind's interaction with Earth’s intrinsic magnetic field. This interaction produces a myriad of large-scale magnetospheric current systems, many of which flow through the polar regions of Earth's ionosphere. Since the ionosphere regulates the circulation of these currents, the aurora's enhancement of the ionospheric conductance becomes a crucial factor for predictive investigations of the magnetosphere - ionosphere coupling during space weather events. While several investigations have attempted to estimate it, the exact factors determining the conductance remain unclear. This impedes both our understanding of the magnetosphere-ionosphere system during space weather events, and predictive capabilities of ground induced currents which pose a serious threat to man-made technology.

Global magnetohydrodynamic (MHD) modeling is a powerful and well-established tool for investigating and predicting the magnetosphere-solar wind interaction. Within these modeling environments, two dedicated models have been developed that estimate auroral precipitation using MHD variables mapped to the ionospheric altitude. Using this modeling ensemble, this thesis addresses the following fundamental questions: (1) What is the individual contribution of each source of precipitation to the total energy deposition in the ionosphere? (2) How does auroral energy deposition affect the electrodynamic functions of the ionosphere and the feedback to the magnetosphere? (3) How do the drivers of ionospheric electrodynamics impact ground-based space weather activity? (4) How does obliquity and dipole field strength impact the shape and strength of the aurora?

The thesis addresses the aforementioned questions by employing the novel modeling approach coupled with suitable ionospheric and inner magnetospheric models. The results were verified through systematic numerical experiments followed by extensive data-model validation studies. Depending on their strengths and location, diverse sources of auroral precipitation were found to impact the total auroral energy flux and ionospheric conductance differently. Diffuse sources formed the largest share of auroral precipitation, contributing to a median 78% of the total energy flux. Discrete sources of precipitation were found to be particularly perceptible to driving conditions, and impacted ionospheric electrodynamics more strongly. The model's enhanced prediction of auroral conductance resulted in greater improvements in space weather prediction. Simulations of the auroral system during a geomagnetic excursion showed that the aurora expands with decreasing magnetic field strength, and rapidly wanders with variations in obliquity. This thesis aims at gaining a significantly improved understanding drivers of auroral precipitation and their interaction with the magnetosphere through a physics-based numerical model which can serve as a predictive tool in space weather operations and planetary simulations.