Preliminary Comparison between Ion Distribution Functions Measured by CLUSTER-CIS
in the Inner Magnetosphere and Ion Distributions Obtained from IMAGE-HENA
Energetic Neutral Atom Image Inversions

Dandouras, I., C. Vallat, P. C:son Brandt, D. G. Mitchell, E. C. Roelof, 
M. Dunlop, H. Reme, A. Balogh

	Data provided by the CIS (Cluster Ion Spectrometry) instruments onboard the
CLUSTER spacecraft are used to survey recent crossings of the inner magnetosphere
and ring current. CIS is capable of obtaining full three-dimensional ion
distributions (about 0 to 40 keV/q) with one spacecraft spin time resolution and
with mass-per-charge composition determination. Events are selected for which the
CLUSTER spacecraft are within the field of view of the HENA (High Energy Neutral
Atom) imager onboard IMAGE. HENA provides energetic neutral atom images with a
high geometric factor and with a 120¡ x 360¡ field of view over the spin. The H+
ion distribution functions obtained in situ by CIS are then compared to the ones
deduced by inverting the HENA hydrogen neutral atom images for the overlapping
energy range of the two instruments (16-40 keV). The magnetic field used to
calculate the ion pitch angle distributions onboard CLUSTER is measured by the
FGM (Flux Gate Magnetometer) instrument. The same magnetic field data allow also
to calculate the ring current density profile along the spacecraft orbit. This
preliminary analysis concerns events obtained both during quiet magnetospheric
conditions (e.g. 04 July 2001 event) and during well-developed ring current
conditions (e.g. 25 July 2001 event).

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To be presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 5-8, 2002.