Modelling Ultra-low Frequency Waves of Earth’s Magnetosphere with Magnetohydrodynamics

Dr Thomas Elsden (University of Glasgow)

Thursday 24th March, 2022 14:00-15:00 Room 110/ZOOM (ID: 984 0117 4999)

Abstract

I realise that I may be the only person working on magnetospheres in the School, and there aren’t all that many of us working on magnetohydrodynamics (MHD) either! With that in mind, I’ll try to make this talk as accessible as possible for anyone with a general interest in how solutions (analytical and numerical) of a set of partial differential equations (i.e. the equations of MHD) can be applied to the Earth’s near space environment.

Earth’s magnetosphere is defined as the space around the Earth which is governed by the effects of Earth’s magnetic field. It is a cavity which is hollowed out of the incoming solar wind and extends about 60,000km towards the Sun. Given that the solar wind is a very non-uniform flow of charged particles, the magnetosphere is constantly perturbed from equilibrium. In response to these perturbations, the magnetosphere vibrates, setting up oscillations in it’s interior, very much like striking a drum. Based on the scale of the system, these oscillations typically have periods of a few seconds to a few minutes, which classifies the Ultra-low Frequency (ULF) band. These waves which propagate across the magnetosphere can also excite local oscillations of individual magnetic field-lines, more like waves on a guitar string. Both oscillations are important for the energy distribution throughout the magnetosphere, the generation of the aurora and the excitation of high-energy particles which can be lethal for orbiting spacecraft.

I will discuss how these different ULF oscillations can be treated with MHD and will hopefully discuss some of the contributions I have made to this area over the last few years. My work is predominantly from a numerical modelling perspective, but I will also likely discuss some early analytical efforts to help explain the key concepts.

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