A new Method for Estimating 3-Dimensional Ionospheric Currents from Ground-Based Magnetometers

Abstract

The ionosphere is a region of the upper atmosphere where a significant rate of photo-ionisation from solar ultraviolet radiation cause an increased plasma density. In this region a system of electrical currents flow, driven by electric fields generated by fluctuating dynamics within the Earths magnetosphere. These fluctuating dynamics are caused by interactions between the magnetosphere and the solar wind and interplanetary magnetic field. The ionospheric current flow causes disturbances in the Earths geomagnetic field called substorms, which have been measured by ground based magnetometers for over 100 years. Different techniques have been developed to determine the ionospheric currents from these measurements, to get a better understanding of the magnetosphere-ionosphere coupling. In this thesis we will investigate what current distributions can be resolved with a large and dense network of ground based magnetometers. With this in mind a new method to estimate ionospheric currents on a simple wireframe model from ground-based magnetic field observations based of general linear inverse methods is presented. The method is based on a Tikhonov type regularization modified to include Kirchoff's current law to regularize the solution in a physically sensible way. The method is tested on a set of artificial current systems to see how well it performs.