Motion of auroral ion outflow structures observed with CLUSTER and IMAGE FUV

L. M. Kistler
Space Science Center, University of New Hampshire,
Durham, New Hampshire, USA

H. U. Frey
Space Sciences Laboratory, University of California,
Berkeley, California, USA

E. Mobius, C. Mouikis, and J. M. Quinn
Space Science Center, University of New Hampshire,
Durham, New Hampshire, USA

B. Klecker
Max-Planck-Institut fŸr Extraterrestriche Physik,
Garching, Germany

H. Reme, J. M. Bosqued, I. Dandouras, and J. A. Sauvaud
Centre d'Etude Spatiale des Rayonnements,
Toulouse, France

A. M. Di Lellis, V. Formisano, and M. F. Marcucci
Istituto di Fisica dello Spazio Interplanetario,
Rome, Italy

C. W. Carlson, J. P. McFadden, and G. K. Parks
Space Sciences Laboratory, University of California,
Berkeley, California, USA

M. McCarthy
Geophysics Program, University of Washington,
Seattle, Washington, USA

A. Korth
Max-Planck-Institut fŸr Aeronomie,
Katlenburg-Lindau, Germany

L. Eliasson and R. Lundin
Swedish Institute of Space Physics,
Kiruna, Sweden

G. Paschmann
Max-Planck-Institut fŸr Extraterrestriche Physik,
Garching, Germany

M. A. Popecki
Space Science Center, University of New Hampshire,
Durham, New Hampshire, USA

S. B. Mende
Space Sciences Laboratory, University of California,
Berkeley, California, USA

J. D. Winningham
Department of Space Sciences, Southwest Research Institute,
San Antonio, Texas, USA

A. N. Fazakerley
Mullard Space Science Laboratory, University College London,
Surrey, United Kingdom


During February 2001 the CLUSTER satellites recorded a number of perigee
passes through the midnight auroral zone. We concentrate on one pass, on 23
February 2001, when structured outflow was observed. Simultaneous observations
of the aurora were available from the FUV instrument on IMAGE. The features in
the ion outflow observed by the Cluster Ion Spectrometry (CIS) experiment are
compared with the auroral activity. Observations from the multiple CLUSTER
spacecraft are used to determine the velocity of the outflow structures. We
find a good correspondence between the observed ion outflow and the auroral
arcs, with the highest energy outflow corresponding to the brightest arcs. The
features at the equatorward edge, which are trapped precipitating ions, are
stationary. In addition, the increased velocity structure at the poleward edge
is also stationary. However, the bulk of the ion outflow structures, which are
observed between these boundaries, are moving equatorward with a velocity of
roughly 7 km/s, which corresponds to a velocity of 0.7 km/s at 100 km. One
feature is observed moving poleward, at the same time that the auroral arc is
expanding poleward. Comparisons with the motion of the auroral arcs and with
the convection velocity measured by the EDI instrument on CLUSTER show that
the motion of the structures in general agrees with the convective motion of
the field lines.

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J. Geophys. Res., 107, A8, 2002