Comparison between in-situ measurements in the inner magnetosphere by CLUSTER 
(CIS and FGM) and ion distributions deduced from IMAGE-HENA energetic neutral 
atom image conversions

Claire Vallat (1), Iannis Dandouras (1), Pontus C:son Brandt (2), 
Donald G. Mitchell (2), Edmond C. Roelof (2), Malcolm Dunlop (3), Henri Reme (1), 
Andre Balogh (3)

(1) Centre d'Etude Spatiale des Rayonnements, Toulouse, France (vallat@cesr.fr)
(2) Applied Physics Laboratory, Johns Hopkins University, Maryland, USA
(3) Blackett Laboratory, Imperial College, London, UK


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 degree x 360 degree 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, using the curlometer technique. This preliminary analysis concerns events 
obtained both during quiet magnetospheric conditions (e.g. 23 March 2002 event) 
and during well-developed ring current conditions (e.g. 12 April 2001 event). The 
results show the complementarity of the two approaches, i.e. local measurements 
and ENA global imaging. The measured ion distribution functions show a variety of 
structures. Furthermore, the latitudinal profile of the ring current is analysed.

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Presented at the 34th COSPAR Scientific Assembly, Houston, Texas, U.S.A.  
10-19 October 2002