IMAGE/HENA: ENA imaging of the plasmasheet during substorms

P. C:son Brandt, E. C. Roelof, R. Demajistre, D. G. Mitchell, S. Mende

September 5, 2001

Abstract

The high energy neutral atom (HENA) imager onboard IMAGE obtained ENA images of the plasmasheet ion distribution at distances out to 14 R_{E} in the nightside magnetosphere. The images were obtained during three substorms with auroral onsets on the 4 october 2000 06:10, 09:22, and 19 September 2000 12:45 UT. We present equatorial ion distributions inverted from the ENA images in the 27-39 keV energy range using a linear inversion method presented byR. Demajistre et al. in this conference. Just prior to dipolarization of the geomagnetic tail observed at geosynchronous by the GOES satellite, the most intense ion distributions start flowing Eartward. For one of the substorms there are weak signatures of a tailward flow initiated at around 8 R_{E} at onset. We show the relation between geosynchronous measurements (LANL, GOES) and global substorm sequences observed by IMAGE/HENA and auroral images observed by IMAGE/FUV. We present estimations on the Earthward flow velocities and discuss the significance and physical implications of the observed tailward flow.