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Ann. Geophys., 19, 1655-1668, 2001
www.ann-geophys.net/19/1655/2001/
© European Geosciences Union 2001
Cluster boundary layer measurements and optical observations at magnetically conjugate sites
J. Moen1,2, J. A. Holtet1, A. Pedersen1, B. Lybekk1, K. Svenes3, K. Oksavik4, W. F. Denig5, E. Lucek6, F. Søraas4, and M. André7
1Department of Physics, University of Oslo, P. O. Box 1048 Blindern, N-0316 Oslo, Norway
2Also at Arctic Geophysics, University Courses on Svalbard, N-9170 Longyearbyen, Norway
3Norwegian Defence Research Establishment, Division for Electronics, P. O. Box 25, N-2007 Kjeller, Norway
4Department of Physics, University of Bergen, N-5007 Bergen, Norway
5Air Force Research Laboratory, Space Vehicles Directorate, Hanscom AFB, MA 01731–3010, USA
6Space and Atmospheric Physics Group, Blackett Laboratory, Imperial College, London, SW7 2BW, UK
7Swedish Institute of Space Physics, Uppsala Division P. O. Box 537, SE-751 21 Uppsala, Sweden
Abstract. The Cluster spacecraft
experienced several boundary layer encounters when flying outbound from the
magnetosphere to the magnetosheath in the dusk sector on 14 January 2001. The
dayside boundary layer was populated by magnetosheath electrons, but not with
quite as high densities as in the magnetosheath itself. The Cluster ground
track was calculated using the Tsyganenko-96 model which appears to be a strong
tool for combining high-altitude satellite and ground observations, given that
the solar wind conditions are known. This paper focuses on identifying auroral
responses corresponding to boundary layer dynamics observed by Cluster. The
first boundary layer encounter studied was a brief visit into a closed LLBL,
most likely due to a boundary wave that travelled tailward over the spacecraft.
A corresponding equatorward and eastward movement was seen in the post-noon
aurora between Greenland and Svalbard. The second boundary encounter was in a
high-latitude cusp, and occurred as a consequence of a transient
reconfiguration of the cusp. The cusp expanded duskward over the spacecraft
into the late post-noon sector. NOAA-12 probed the 16:30 MLT sector of this
auroral activity, and measured a 1.4 keV electron beam located poleward of the
30 keV electron-trapping boundary. A sequence of three moving auroral forms
emanating from this active region are likely candidates for flux transfer
events. The auroral signatures are discussed in relation to earlier
observations, and appear to be an example of accelerated electrons/discrete
post-noon aurora on open magnetic field lines.
Key words. Ionosphere (particle
precipitation) Magnetospheric physics (auroral phenomena; magnetopause, cusp
and boundary layers)
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