Explosive energy release in space plasmas: unravelling the magnetospheric dynamics of substorms

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The substorm is a common space weather disturbance, which includes a rapid enhancement in the nightside aurora, magnetic disturbances on the ground, enhancements in the ring current and radiation belts and heating of plasma further out in the magnetosphere. Substorms release ~1 PJ (1015 J) of energy in ~30 min, with approximately half of this energy being dumped into the atmosphere. This energy release and the processes associated with it have the potential to be harmful to technology in space and on the ground, making substorms a key component of space weather.In the standard substorm model, substorms have three phases: a growth phase of ~1 hour during which reconnection between the magnetosphere and the solar wind adds energy into Earth's magnetotail; an expansion phase lasting ~20 min in which some of this energy is rapidly released, creating bright aurora and reconfiguring Earth's magnetic field; and a recovery phase that lasts 1-2 hours during which energy continues to be released but at a decreasing rate and the system begins to return to the pre-substorm state.The reconfiguration of Earth's magnetotail magnetic field by reconnection is a key component of the substorm cycle. Studies have shown that signatures of bursts of reconnection are a key component of the substorm cycle and may transport significant amounts of magnetic flux through the system. They have also been inferred to be a key part in initiating the substorm activity (the so-called 'outside-in' model of substorm initiation). However, recent studies have shown that the initial signatures of the substorm expansion phase are those of a plasma instability in the inner magnetosphere and do not require reconnection to have been initiated first. Given that reconnection is considered to be a key component of global substorm activity, this leaves an apparent disconnect between the initiation of the instability and the reconfiguration of the magnetic field.This project aims to improve our understanding of the substorm processes within the magnetosphere, placing observations of the signatures of reconnection, magnetotail reconfiguration and plasma instabilities in relative context: (i) comparing the relative timing of different in-situ and remotely detected substorm signatures including magnetospheric fast flows and ULF wave growth(ii) determining which observational features are common to all substorms and examining the implications of the presence or lack thereof of non-common features (iii) examining the occurrence and impact of 'substorm signatures' during periods of substorm and non-substorm activity.This project will involve the examination of a variety of data sources including in-situ observations from missions such as Cluster, THEMIS and MMS as well as ground-based data from magnetometer chains and auroral all-sky cameras.