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Ann. Geophys., 23, 867-876, 2005
www.ann-geophys.net/23/867/2005/
© European Geosciences Union 2005
Latitude-energy structure of multiple ion beamlets in Polar/TIMAS data in plasma sheet boundary layer and boundary plasma sheet below 6 RE radial distance: basic properties and statistical analysis
P. Janhunen1, A. Olsson2, W. K. Peterson3, and J. D. Menietti4
1Finnish Meteorological Institute, Space Research, Helsinki, Finland
2Swedish Institute of Space Physics, Uppsala, Sweden
3LASP, University of Colorado, Boulder, Colorado, USA
4University of Iowa, Iowa, USA
Abstract. Velocity dispersed ion signatures (VDIS) occurring at the plasma
sheet boundary layer (PSBL) are a well reported feature. Theory has, however,
predicted the existence of multiple ion beamlets, similar to VDIS,
in the boundary plasma sheet (BPS), i.e. at latitudes below the
PSBL. In this study we show evidence for
the multiple ion beamlets in Polar/TIMAS ion data and basic
properties of the ion beamlets will be presented. Statistics of the
occurrence frequency of ion multiple beamlets show that they are most
common in the midnight MLT sector and for altitudes above 4 RE,
while at low altitude (≤3 RE), single beamlets at PSBL (VDIS) are more
common. Distribution functions of ion beamlets in velocity space
have recently been shown to correspond to 3-dimensional hollow spheres,
containing a large amount of free energy. We also study correlation with ~100
Hz waves and electron anisotropies and consider the
possibility that ion beamlets correspond to stable auroral arcs.
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