The drivers and timescales of solar wind-magnetosphere-Ionosphere coupling in global MHD simulations

The interaction between the solar wind and the terrestrial magnetosphere-ionosphere system is highly dynamic and non-linear, strongly influencing conditions in near-Earth space. Understanding the coupling between each component of the system is crucial to mitigating societal effects, known as space weather. Global magnetohydrodynamic (MHD) simulations are an invaluable tool in studying this interaction. This thesis entails the use of the Gorgon MHD code for simulating the Earth’s magnetosphere. An updated version of the code is presented, including a newly developed ionosphere module which is tested and benchmarked to validate its proper coupling to the magnetosphere. The model is applied to study the effect of the geomagnetic dipole tilt angle on magnetopause reconnection and ionospheric current systems. The location of the reconnection line is identified for tilt angles up to 90°, with reconnection found to be weaker and more unsteady at large tilt angles. The tilt introduces a North-South asymmetry driving more FAC in the sunward-facing hemisphere, highlighting the sensitivity to onset time in the potential impact of a severe space weather event. An idealised example of such an event is then simulated by impacting the magnetosphere with an interplanetary shock. The location and intensity of dayside reconnection is found to be highly time-dependent following impact, with reconnection enhanced in the vicinity of the shock. These results suggest that steady models of reconnection may not be reliable immediately after onset. Finally, an extended version of the code is implemented to simulate a real geomagnetic storm. The key response timescales of the magnetosphere-ionosphere system to the varying solar wind are investigated, and found to be consistent with those of global convection, being sensitive to the particular mode of driving. It is shown that Gorgon is a capable space weather modelling tool, forming a crucial step towards future operational forecasting purposes.Open Acces

Electromagnetic induction in the icy satellites of Uranus

The discovery of subsurface oceans in the outer solar system has transformed our perspective of ice worlds and has led to consideration of their potential habitability. The detection and detailed characterisation of induced magnetic fields due to these subsurface oceans provides a unique ability to passively sound the conducting interior of such planetary bodies. In this paper we consider the potential detectability of subsurface oceans via induced magnetic fields at the main satellites of Uranus. We construct a simple model for Uranus’ magnetospheric magnetic field and use it to generate synthetic time series which are analysed to determine the significant amplitudes and periods of the inducing field. The spectra not only contain main driving periods at the synodic and orbital periods of the satellites, but also a rich spectrum from the mixing of signals due to asymmetries in the uranian planetary system. We use an induction model to determine the amplitude of the response from subsurface oceans and find weak but potentially-detectable ocean responses at Miranda, Oberon and Titania, but did not explore this in detail for Ariel and Umbriel. Detection of an ocean at Oberon is complicated by intervals that Oberon will spend outside the magnetosphere at equinox but we find that flybys of Titania with a closest approach altitude of 200 km would enable the detection of subsurface oceans. We comment on the implications for future mission and instrument design

Climatological predictions of the auroral zone locations driven by moderate and severe space weather events

Auroral zones are regions where, in an average sense, aurorae due to solar activity are most likely spotted. Their shape and, similarly, the geographical locations most vulnerable to extreme space weather events (which we term ‘danger zones’) are modulated by Earth’s time-dependent internal magnetic field whose structure changes on yearly to decadal timescales. Strategies for mitigating ground-based space weather impacts over the next few decades can benefit from accurate forecasts of this evolution. Existing auroral zone forecasts use simplified assumptions of geomagnetic field variations. By harnessing the capability of modern geomagnetic field forecasts based on the dynamics of Earth’s core we estimate the evolution of the auroral zones and of the danger zones over the next 50 years. Our results predict that space-weather related risk will not change significantly in Europe, Australia and New Zealand. Mid-to-high latitude cities such as Edinburgh, Copenhagen and Dunedin will remain in high-risk regions. However, northward change of the auroral and danger zones over North America will likely cause urban centres such as Edmonton and Labrador City to be exposed by 2070 to the potential impact of severe solar activity