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

Abstract

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.