ANGEO

Annales Geophysicae

ANGEO

1432-0576

Copernicus GmbH

Göttingen, Germany

10.5194/angeo-23-867-2005

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

Janhunen

¹ Olsson

² Peterson

W. K.

³ Menietti

J. D.

⁴

Finnish Meteorological Institute, Space Research, Helsinki, Finland

Swedish Institute of Space Physics, Uppsala, Sweden

LASP, University of Colorado, Boulder, Colorado, USA

University of Iowa, Iowa, USA

30 03 2005

23 3 867 876

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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.