HR: 0800h
AN: SM11A-0306    [Abstracts]
TI: Cluster observations of the Earth's quasi-parallel bow shock
AU: * Lucek, E A
EM: e.lucek@imperial.ac.uk
AF: Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ, United Kingdom
AU: Horbury, T S
EM: t.horbury@imperial.ac.uk
AF: Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ, United Kingdom
AU: Dandouras, I
EM: iannis.dandouras@cesr.fr
AF: Centre d'Etude Spatiale des Rayonnements, 9 Ave. du Colonel Roche B.P. 4346, Toulouse, F-31028, France
AU: R{è}me, H
EM: Henri.Reme@cesr.fr
AF: Centre d'Etude Spatiale des Rayonnements, 9 Ave. du Colonel Roche B.P. 4346, Toulouse, F-31028, France
AB: Cluster observations of the Earth's quasi-parallel shock are used to investigate properties of the transition and the role of magnetic pulsations in the shock process. Previous studies have shown that the parallel shock is both extended in space and rapidly varying in time. Embedded within it are magnetic pulsations that grow from upstream waves and are thought to play a key role in the thermalisation process. We use crossings at small spacecraft separations to show that pulsations grow on a timescale of only a few seconds. We then use an example of a shock crossing when the spacecraft were a few thousand kilometers apart to demonstrate that the transition was, in this case, confined to a distance of less than 2500 km. In particular, in the context of data showing that the overall extent of the pulsations exceeds 1000 km, this suggests that the thickness of the shock layer over which the bulk of plasma thermalisation occurs is narrow, containing only one or at most a few pulsations. The small scale spatial properties of structures within the shock are difficult to extract independently of their time evolution, but we present a crossing with a favourable tetrahedron formation at which two pairs of spacecraft observed the same magnetic signatures simultaneously. We show that signatures of these pulsations are consistent with their refraction as they are convected anti-sunwards, as predicted by simulation work, and that they are coherent over a distance of at least 1300 km parallel to the expected shock surface.
DE: 7851 Shock waves (4455)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting