THE ION EXPERIMENT ONBOARD THE INTERBALL-AURORA SATELLITE INITIAL RESULTS ON VELOCITY-DISPERSED STRUCTURES IN THE CLEFT AND INSIDE THE AURORAL OVAL

The Toulouse ION experiment flown on the Russian Interball-Aurora miss ion performs simultaneous ion and electron measurements. Two mass spec trometers looking in opposing directions perpendicular to the satellit e spin axis, which points toward the sun, measure ions in the mass and energy ranges 1-32 amu and similar to 0-14 000 eV. Two electron spect rometers also looking in opposing directions perform measurements in t he energy range similar to 10 eV-20 000 eV. The Interball-Aurora space craft was launched on 29 August 1996 into a 62.8 degrees inclination o rbit with an apogee of similar to 3 R-E The satellite orbital period i s 6 h, so that every four orbits the satellite sweeps about the same r egion of the auroral zone; the orbit plane drifts around the pole in s imilar to 9 months. We present a description of the ION experiment and discuss initial measurements performed in the cusp near noon, in the polar cleft at dusk, and inside the proton aurora at dawn. Ion-dispers ed energy structures resulting from time-of-flight effects are observe d both in the polar cleft at similar to 16 hours MLT and in the dawnsi de proton aurora close to 06 hours MLT. Magnetosheath plasma injection s in the polar cleft, which appear as overlapping energy bands in part icle energy-time spectrograms, are traced backwards in time using a pa rticle trajectory model using 3D electric and magnetic field models. W e found that the cleft ion source is located at distances of the order of 18 R-E from the earth at about 19 MLT, i.e., on the flank of the m agnetopause. These observations are in agreement with flux transfer ev ents (FTE) occurring not only on the front part of the magnetopause bu t also in a region extending at least to dusk. We also show that, duri ng quiet magnetic conditions, time-of-flight ion dispersions can also be measured inside the dawn proton aurora. A method similar to that us ed for the cleft is applied to these auroral energy dispersion signatu res. Unexpectedly, the ion source is found to be at distances of the o rder of 60-80 R-E, at the dawn flank of the magnetosphere. These resul ts are discussed in terms of possible entry, acceleration, and precipi tation mechanisms.