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Multipoint measurements of magnetospheric substorms

Project: Funded ProjectResearch


Substorms are one of the principal mechanisms that regulate the coupling between the Earth’s magnetic field and the interplanetary magnetic field (IMF) embedded within the solar wind. At the dayside magnetopause, magnetic reconnection between “closed” terrestrial magnetic field lines (field lines that extend from one geomagnetic pole to the other) and the IMF results in “open” magnetic field lines with one end anchored in the Earth’s polar cap while the other remains embedded in the solar wind. Open magnetic field lines created by this process are carried into the Earth’s magnetic tail by the anti-sunward motion of the solar wind. Since the substorm concept was first introduced over 40 years ago, their role in the closure of magnetic flux in the Earth’s magnetotail has been actively debated. Four decades of ground- and space-based observations have led to the development of two competing models that rely upon different physical mechanisms to explain the sequence of cause and effect in the magnetosphere that result in the closure of open magnetic flux by reconnection in the tail and the auroral disturbances observed in the midnight sector auroral zones.

In order to determine the location of substorm onset in the tail (and discriminate between the currently proposed models) it is necessary to compare the timing of the auroral signatures of substorm onset with simultaneous in situ field and particle measurements at several locations in the magnetotail. This will reveal the sequence of events during substorm expansion phase onset. Previous attempts to resolve this uncertainly have been thwarted by the insufficient spatial coverage of in situ satellite measurements in the magnetotail, the inadequate temporal resolution of the space-based auroral imagers used to time the auroral signatures of substorm onset, the limited spatial coverage of ground-based auroral imagers, and the unclear relationship between various ground-based techniques employed to estimate the reconnection rate in the tail.

This programme of research exploited an unprecedented combination of space- and ground-based experiments in order to study the time-history of auroral breakup, current disruption, and lobe flux disconnection in the tail.