Earth's magnetic field shields humanity from charged particles streaming from the sun, known as the solar wind, forming a cavity in space. This cavity, also called Earth's magnetosphere, is populated by charged particles trapped in the magnetic field configuration. During strong solar wind driving or coronal mass ejections, the particle populations undergo drastic changes, including enhancements of their fluxes by several orders of magnitude. This enhancement is not only measurable on the ground as a weakening of Earth's magnetic field but can also harm the satellite infrastructure through surface charging and deep dielectric charging effects. Furthermore, field-aligned electrons can reach Earth's atmosphere, where they cause chemical changes such as the destruction of ozone or light phenomena, also known as the aurora. This dissertation studies one particular particle population, the electron ring current, which is the deciding factor in whether surface charging effects on spacecraft will occur. This dissertation aims to broaden our knowledge about the dynamics of the ring current electrons and how we can better predict the evolution of the ring current during geomagnetic storms. To this end, we employed a numerical model based on the Fokker-Planck equation to study the time evolution of the four-dimensional phase space density of ring current electrons. We performed a sensitivity analysis of the 10 keV electron flux during minor and strong geomagnetic storms to find the most important parameters that control the dynamics of the ring current. During this work, we found systematic discrepancies between the model predictions and satellite observations during strong geomagnetic storms, which we further explored in a subsequent study. We found that these discrepancies, which can reach several orders of magnitude, are caused by incorrect parameterization of the scattering rates or electrons in the pre-midnight sector. To further test the existence of this missing loss process, we developed a new method for estimating the precipitating electron flux from simulations. The new method allowed us to validate the loss of electrons from the ring current by comparing it with measurements taken at low Earth orbit, confirming the initial hypothesis that the scattering rates of electrons in the pre-midnight sector are too low. To strengthen our model's predictive capabilities, we tested data assimilation techniques. These techniques allow the blending of satellite observations with the model to create a more accurate representation of the global state. We performed the first validation of a data-assimilative ring current model against a fully independent data set and showed the effectiveness of data assimilation. Assimilating data from a single spacecraft was sufficient to correct the model state globally, as shown by the validation against the independent data set. This dissertation contributed to our understanding of our modeling capabilities of the particle populations of Earth's magnetosphere and how they are coupled. The results presented in the dissertations will help build more reliable forecasting models of the electron ring current, reducing the particles' negative effects on the satellite infrastructure.
Bernhard Haas (2026) studied this question.