Study of waves and structures at the boundaries of magnetospheres

Plasma exists in abundance throughout the universe and governs a large number of astrophysical processes that have been observed and are of interest. Studying the interactions of plasma with magnetic field waves, magnetic dipoles and counter-streaming plasma flows can provide insight in the fundamental physics that govern the universe and its evolution. In order to study these phenomena in-situ, we are limited to spacecraft measurements in the heliosphere. Planetary missions are the ones that provide the largest quantities of measurements of the same phenomenon, due to their orbital parameters. On the other hand, the cost of these missions, generally limits them to a single spacecraft with the exception of spacecraft that orbit the Earth.
This thesis is mainly concerned with the study of the interactions of plasma at the boundary of magnetic dipoles and the electromagnetic waves that are present in such environments. Upstream of the boundary between the Earth’s magnetic field and the interplanetary magnetic field, the magnetopause (average distance from Earth ∼ 10RE ∼ 63000 km), a region of plasma heated by the bow shock exists, the magnetosheath. This region is rich in electromagnetic emissions and magnetic structures. The physical processes at the bow shock can provide insight in astrophysical phenomena. The interaction of the waves in the magnetosheath with the surrounding plasma is also of great interest as they govern the behaviour of the plasma.
Specifically this thesis initially examines the physical processes at the bow shocks of Earth and Venus. The magnetic environments of the two planets are different, as Venus does not have a magnetic field generated by the rotation of its core, unlike Earth. This means that there is benefit in studying both under the same framework in order to determine the underlying physics. The work then continuous with the examination of electromagnetic emissions downstream of the Earth’s bow shock. These waves have been named lion roars and their exact origin is unclear, although they have been shown to change the properties of the plasma they interact with.