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Ann. Geophys., 19, 1411-1420, 2001
www.ann-geophys.net/19/1411/2001/
© European Geosciences Union 2001
Observations of the spatial and temporal structure of field-aligned beam and gyrating ring distributions at the quasi-perpendicular bow shock with Cluster CIS
E. Möbius1, H. Kucharek2, C. Mouikis1, E. Georgescu2, L. M. Kistler1, M. A. Popecki1, M. Scholer2, J. M. Bosqued3, H. Rème3, C. W. Carlson5, B. Klecker2, A. Korth6, G. K. Parks5, J. C. Sauvaud3, H. Balsiger4, M.-B. Bavassano-Cattaneo8, I. Dandouras3, A. M. DiLellis8, L. Eliasson9, V. Formisano8, T. Horbury10, W. Lennartsson7, R. Lundin9, M. McCarthy11, J. P. McFadden5, and G. Paschmann2
1Dept. of Physics and Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH, USA
2Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
3Centre d’Etude Spatiale et Rayonnement, Toulouse, France
4Physikalisches Institut der Universität Bern, Switzerland
5Space Sciences Laboratory, University of California, Berkeley, USA
6Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany
7Lockheed-Martin Palo Alto Research Laboratory, Palo Alto, USA
8Istituto di Fisica dello Spazio Interplanetario, Rome, Italy
9Institut for Rømdfysik, Kiruna, Sweden
10Imperial College, London, UK
11Space Program, University of Washington, USA
Abstract. During the early orbit
phase, the Cluster spacecraft have repeatedly crossed the perpendicular Earth’s
bow shock and provided the first multi-spacecraft measurements. We have
analyzed data from the Cluster Ion Spectrometry experiment (CIS), which
observes the 3D-ion distribution function of the major species in the energy
range of 5 eV to 40 keV with a 4 s resolution. Beams of reflected ions were
observed simultaneously at all spacecraft locations and could be tracked from
upstream to the shock itself. They were found to originate from the same
distribution of ions that constitutes the reflected gyrating ions, which form a
ring distribution in the velocity space immediately upstream and downstream of
the shock. This observation suggests a common origin of ring and beam
populations at quasi-perpendicular shocks in the form of specular reflection
and immediate pitch angle scattering. Generally, the spatial evolution across
the shock is very similar on all spacecraft, but phased in time according to
their relative location. However, a distinct temporal structure of the ion
fluxes in the field-aligned beam is observed that varies simultaneously on all
spacecraft. This is likely to reflect the variations in the reflection and
scattering efficiencies.
Key words. Interplanetary physics
(planetary bow shocks; energetic particles; instruments and techniques)
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