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Ann. Geophys., 25, 1001-1009, 2007
www.ann-geophys.net/25/1001/2007/
© European Geosciences Union 2007
Prelude to THEMIS tail conjunction study
A. T. Y. Lui1, Y. Zheng1, Y. Zhang1, V. Angelopoulos2, G. K. Parks2, F. S. Mozer2, H. Rème3, L. M. Kistler4, M. W. Dunlop5, G. Gustafsson6, and M. G. Henderson7
1JHU/APL, Laurel, MD 20723-6099, USA
2Space Sciences Laboratory, UCB, Berkeley, CA, USA
3CESR, BP4346, 31028 Toulouse Cedex 4, Toulouse, France
4University of New Hampshire, Durham, NH, USA
5Space Science and Technology Department, RAL, Chilton, Didcot, Oxfordshire OX11 0QX, UK
6Swedish Institute of Space Physics, Uppsala Division, 755 91 Uppsala, Sweden
7LANL, MS D466, Los Alamos, NM, USA
Abstract. A close conjunction of several satellites (LANL, GOES,
Polar, Geotail, and Cluster) distributed from the geostationary altitude to
about 16 RE downstream in the tail occurred during substorm activity as
indicated by global auroral imaging and ground-based magnetometer data. This
constellation of satellites resembles what is planned for the THEMIS (Time
History of Events and Macroscopic Interactions during Substorms) mission to
resolve the substorm controversy on the location of the substorm expansion
onset region. In this article, we show in detail the dipolarization and
dynamic changes seen by these satellites associated with two onsets of
substorm intensification activity. In particular, we find that
dipolarization at ~16 RE downstream in the tail can occur with
dawnward electric field and without plasma flow, just like some near-Earth
dipolarization events reported previously. The spreading of substorm
disturbances in the tail coupled with complementary ground observations
indicates that the observed time sequence on the onsets of substorm
disturbances favors initiation in the near-Earth region for this THEMIS-like
conjunction.
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