Foster, A; (2017) Structure and dynamics of plasma layers associated with magnetic reconnection in the solar wind - Cluster spacecraft observations. Doctoral thesis , UCL (University College London).

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Abstract

We study magnetic reconnection events in the solar wind, using observations by the 4 Cluster spacecraft during periods where they are located in this region. Use of data from the 4 Cluster spacecraft allows us to look at the three dimensional structure of events at high time resolution, up to 0.04s for magnetic field data. We present a case study of a magnetic reconnection event that was observed within the solar wind flow on the 2nd March 2006. This event enables us to test the consistency of the temporal and spatial structure of magnetic reconnection from large- to small-scales. We use data from the four Cluster spacecraft to study the three-dimensional structure of the event at sub-second resolution. This showed significant differences in the magnetic field data between spacecraft, despite the fact that they are separated by distances of only order 10^4 km. Thus the structure appears to have variations over relatively small scales. We conclude that magnetic reconnection in the solar wind is not necessarily large-scale but, contrary to previous results, may be somewhat patchy in nature. We also present a sketch for magnetic reconnection which has a more complicated structure than previous sketches of magnetic reconnection events in the solar wind. In addition we have introduced the observed magnetic field and ion velocities over the event depending on the inflow parameters and the strength of the diamagnetic effect of the outflow ions and electrons. We also compare a similarly structured mathematical model (Owen and Cowley 1987b) with 3 case studies in the solar wind and compare the outflows predicted by the model with the observed outflows. Finally we present the workings of an algorithm to find magnetic reconnection events in the solar wind and the subsequent statistical analysis of the events found. The statistical analysis revealed that magnetic reconnection events occur for a wide range of solar wind conditions. We found that the exhaust speed was between 0.1 - 2 x Alfvén speed leading to the conclusion that, for ratios of less than 1, not all the magnetic field energy is converted to kinetic energy and, for those ratios greater than 1, that the reconnection site had a higher local Alfvén speed than where the exhaust was observed by the spacecraft. We also compared the data between Cluster spacecraft and determined that the spacecraft usually witness magnetic field structures that are strongly correlated with each other.

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