Varsani, A; (2015) Microscale dynamics of the Earth's magnetopause and its boundary layer - cluster observations. Doctoral thesis , UCL (University College London).

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Abstract

This thesis presents original research on the solar wind interactions with the Earth's magnetosphere, with main focus on processes occurring at the magnetopause. Such processes are often difficult to fully access observationally as their typical timescales are faster than the particle data cadence which is usually limited to the spin resolution, typically a few seconds, of the spacecraft. Here, a novel method is applied to data from the Cluster mission in order to acquire the pitch angle distribution of particles at 0.125 second per sample, the highest-temporal resolution available at the time of research described here. Two chapters of this thesis present results based on the exploitation of this high-temporal resolution dataset. The first study presents analysis of Cluster observations of the substructure of a flux transfer event (FTE), which reveals unprecedented details of the FTE. The work resolves previously unseen layers of the FTE, and provides evidence of recent reconnection in the outer layers (Varsani et al., 2014). The second study focuses on the microscale dynamics within Kelvin-Helmholtz waves at the dusk flank of the magnetopause. This analysis reveals the presence of boundary layer plasma travelling faster than the sheath (BPFTS), which appears to be the result of magnetic reconnection even though, contrary to earlier suggestions, there is no evidence of rolled-up KHI vortices. The final study conducts a survey of Cluster observations to compare the two techniques for identification of rolled-up KHI vortices: the low-density faster than sheath (LDFTS) and boundary plasma faster than sheath (BPFTS) methods. The results show that since BPFTS is more rigorously defined, based on the magnetopause transition parameter (TP), it eliminates ambiguity in the observation of the plasma depletion layer instead of the boundary layer. Furthermore, the flow directions identified by BPFTS method, are consistent with the expectations of the KHI growth criteria.

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