INITIAL OBSERVATIONS OF FINE PLASMA STRUCTURES AT THE FLANK MAGNETOPAUSE WITH THE COMPLEX PLASMA ANALYZER SCA-1 ONBOARD THE INTERBALL-TAIL-PROBE

The fast plasma analyzer EU-1 of the SCA-1 complex plasma spectrometer is installed onboard the Interball Tail Probe (Interball-1). It provi des fast three-dimensional measurements of the ion distribution functi on on the low-spin-rate Prognoz satellite (about 2min). The EU-1 ion s pectrometer with virtual aperture consists of two detectors with 16 E/ Q marrow-angle analyzers and electrostatic scanners. This configuratio n allows one to measure the ion distribution function in three dimensi ons (over 15 energy steps in 50 eV/Q=5.0 keV/Q energy range in 64 dire ctions) in 7.5 s, which makes it independent of the slow rotation spee d of the satellite. A description of the instrument and its capabiliti es is given. We present here the preliminary results of measurements o f ions for two cases of the dawn low- and mid-latitude magnetopause cr ossings. The properties of observed ion structures and their tentative explanation are presented. The 12 September 1995 pass at low latitude at about 90 degrees solar-zenith angle on the dawn side of the magnet osphere is considered in more detail. Dispersive ions are seen at the edge of the magnetopause and at the edges of subsequently observed pla sma structures. Changes in ion velocity distribution in plasma structu res observed after the first magnetopause crossings may be plasma blob s penetrating the magnetosphere. Observed variations of plasma paramet ers near magnetopause structures suggest nonstationary reconnection as the most probable mechanism for observed structures.