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MSSL Space Plasma Science Nuggets

Structure and variability of the auroral acceleration region

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The Aurora Australis seen from the International Space Station (ISS-029). Courtesy: NASA

Bright auroral arc appear when charged particles from the magnetosphere are accelerated into the upper atmosphere. Collisions between charged particles and neutrals excite the electrons in the neutral particles which then de-excite by emitting auroral light. Particles, in particular electrons, are accelerated out of the magnetosphere and into the atmosphere by magnetic-field-aligned electric potential drops in a region known as the auroral acceleration region (AAR). In a recent paper, Forsyth et al. [2012] investigated the temporal variability and spatial structure in one such region.

What is the source of magnetotail flux-ropes?

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Artist impression of the Earth's bow shock. (c) UCL

Travelling compression regions (TCRs) are perturbations in the magnetotail lobe magnetic field caused by structures moving Earthward or tailward within the plasma sheet. Previous works have suggested that these structures are created by either time-dependant reconnection occurring at a single X-line, forming a flux-bulge-type structure, or space-variant reconnection at multiple X-lines, forming flux-rope-type structures. By analysing a TCR and its source structure using the Cluster spacecraft, Beyene et al. (2011) have endeavoured to determine which of these mechanisms creates TCRs.

Particle Distributions in the Magnetotail

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Artists impression of the plasma regions of the magnetosphere. (c) UCL 2011

For the first time, Walsh et al. have examined, in detail, the particle distributions in the magnetotail to determine the average pitch angle distributions. 

Calculating currents from four spacecraft

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Artist's impression of the Cluster quartet. (c) ESA

Ampere's law tells us that the curl of a magnetic field is proportional to current density. In order to measure the curl of a magnetic field in space, one needs to know approximate the variation of the magnetic field between four non-coplanar points. Such measurements are achieved by the Cluster quartet.

Discovery of the 'Travelling Magnetopause Erosion Region'

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A 3D cut showing regions of the magnetosphere. FTE formation occurs on or near the subsolar magnetopause (yellow circle).

Recent work by Owen et al. has shed new light on the structure of the magnetopause following bursts of reconnection through the discovery of 'Travelling Magnetopause Erosion Regions'.

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