TY  - JOUR
IS  - 7
N1  - Copyright 2006 by the American Geophysical Union
VL  - 33
AV  - public
Y1  - 2006/04/12/
TI  - Temporal evolution of a staircase ion signature observed by Cluster in the mid-altitude polar cusp
A1  - Escoubet, CP
A1  - Bosqued, JM
A1  - Berchem, J
A1  - Trattner, KJ
A1  - Taylor, MGGT
A1  - Pitout, F
A1  - Laakso, H
A1  - Masson, A
A1  - Dunlop, M
A1  - Reme, H
A1  - Dandouras, I
A1  - Fazakerley, A
KW  - Flux-transfer events
KW  -  Interplanetary magnetic-field
KW  -  Low-altitude observations
KW  -  Magnetopause reconnection
KW  -  Precipitation
KW  -  Aurora
KW  -  Edge
JF  - Geophysical Research Letters
UR  - http://dx.doi.org/10.1029/2005GL025598
PB  - Amer Geophysical Union
SN  - 0094-8276
N2  - 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.
ID  - discovery162631
ER  -