%0 Journal Article
%@ 0094-8276
%A Escoubet, CP
%A Bosqued, JM
%A Berchem, J
%A Trattner, KJ
%A Taylor, MGGT
%A Pitout, F
%A Laakso, H
%A Masson, A
%A Dunlop, M
%A Reme, H
%A Dandouras, I
%A Fazakerley, A
%D 2006
%F discovery:162631
%I Amer Geophysical Union
%J Geophysical Research Letters
%K Flux-transfer events, Interplanetary magnetic-field, Low-altitude observations, Magnetopause reconnection, Precipitation, Aurora, Edge
%N 7
%T Temporal evolution of a staircase ion signature observed by Cluster in the mid-altitude polar cusp
%U https://discovery.ucl.ac.uk/id/eprint/162631/
%V 33
%X We use the Cluster string of pearls configuration to investigate temporal variations of ion precipitation in the mid-altitude polar cusp. On 7 Aug. 2004, Cluster 4 was moving poleward through the Northern cusp, followed by Cluster 1, Cluster 2, and finally Cluster 3. The Wind spacecraft detected a Southward turning of the Interplanetary Magnetic Field ( IMF) at the beginning of the cusp crossings and IMF-Bz stayed negative throughout. Cluster 4 observed a high energy step in the ion dispersion around 1 keV on the equatorward side of the cusp. C1, entering the cusp around 1 minute later, did not observe the high energy step anymore but a partial dispersion with a low energy cut-off reaching 100 eV. About 9 min later, C3 entered the cusp and observed a full ion dispersion from a few keV down to around 50 eV. The open-closed boundary, identified by electron precipitation, was initially moving equatorward at a rate of -0.43 degrees ILAT/minute at the beginning of the event and then slowed down to -0.16 degrees ILAT/minute, suggesting the erosion of the dayside magnetosphere under IMF Southward. This event is explained by the onset of dayside reconnection when the IMF turned southward; the step being the first signature of the reconnection that would then evolve as a full dispersion as reconnection goes on. We observed 1-3 keV ions near the open-closed boundary on the three spacecraft crossings that suggests a continuous reconnection during about 9 minutes.
%Z Copyright 2006 by the American Geophysical Union