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Ann. Geophys., 19, 611-619, 2001
www.ann-geophys.net/19/611/2001/
© European Geosciences Union 2001
A new, unique signature of the true cusp
W. R. Keith1, J. D. Winningham1, and O. Norberg2
1Southwest Research Institute, P. O. Drawer 28510, San Antonio, Texas 78228-0510, USA
2Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden
Abstract. The "cusp
proper" is generally understood to be the region enclosed by the outermost
magnetospheric field lines as they map to low altitudes. It is therefore a
weak-field region with continuous contact with magnetosheath plasma. Data from
the recent Astrid-2 Swedish microsatellite are presented which show a new,
unique signature (dubbed the "true cusp") during cusp crossings that
can now be shown to be consistently present and with which one can redefine the
physical meaning and topology of the cusp. Similar crossings made by the DE-2,
UARS and DMSP-F10 satellites also show this same, unique signature although in
most cases the spatial resolution was much less than that of the Astrid-2
MEDUSA spectrometer. The presence of concurrent features of the same scale size
as the plasma in the energetic particle, field and wave power data shows that
this is a real structural feature and not a coincidental structure among plasma
instruments. The persistence of this feature may lend new insight into the
dynamics of the cusp and magnetospheric particle entry.
Key words. Magnetospheric physics
(magnetopause, cusp, arid boundary layers; magnetospheric configuration and
dynamics)
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