Abstract
The fast plasma analyzer EU-1 of the SCA-1 complex plasma spectrometer is installed onboard the Interball Tail Probe (Interball-1). It provides fast three-dimensional measurements of the ion distribution function on the low-spin-rate Prognoz satellite (about 2min). The EU-1 ion spectrometer with virtual aperture consists of two detectors with 16 E/Q narrow-angle analyzers and electrostatic scanners. This configuration allows one to measure the ion distribution function in three dimensions (over 15 energy steps in 50 eV/Qâ5.0 keV/Q energy range in 64 directions) in 7.5 s, which makes it independent of the slow rotation speed of the satellite. A description of the instrument and its capabilities is given. We present here the preliminary results of measurements of ions for two cases of the dawn low- and mid-latitude magnetopause crossings. The properties of observed ion structures and their tentative explanation are presented. The 12 September 1995 pass at low latitude at about 90° solar-zenith angle on the dawn side of the magnetosphere is considered in more detail. Dispersive ions are seen at the edge of the magnetopause and at the edges of subsequently observed plasma structures. Changes in ion velocity distribution in plasma structures observed after the first magnetopause crossing suggest that what resembles multiple magnetopause crossings may be plasma blobs penetrating the magnetosphere. Observed variations of plasma parameters near magnetopause structures suggest nonstationary reconnection as the most probable mechanism for observed structures.
Highlights
The complex plasma spectrometer SCA-1 is intended to measure characteristics of magnetospheric ions on the Tail Probe of the Interball Project
Quasi-periodic pulses of magnetosheath-like plasma on magnetic field lines near the dawn magnetopause observed on ISEE 1/2 were interpreted as evidence for the strong diffusion of magnetosheath plasma across the magnetopause, and the K-H instability at the inner edge of the low-latitude boundary layer (LLBL) (Sckopke et al, 1981), as evidence for magnetic merging and the formation of twisted flux ropes of interconnected magnetosheath and magnetospheric field lines (Paschmann et al, 1982), and as quasiperiodic magnetopause motions and observation of draped northward magnetosheath magnetic field lines in the plasma depletion layer (Sibeck et al, 1990)
It allows one to redirect the apertures of all eight individual narrow-angle electrostatic analyzers simultaneously, so they are looking in eight evenly spaced directions along the cone with an opening angle controlled by the electrostatic scanner
Summary
The complex plasma spectrometer SCA-1 is intended to measure characteristics of magnetospheric ions on the Tail Probe of the Interball Project. Quasi-periodic pulses of magnetosheath-like plasma on magnetic field lines near the dawn magnetopause observed on ISEE 1/2 were interpreted as evidence for the strong diffusion of magnetosheath plasma across the magnetopause, and the K-H instability at the inner edge of the LLBL (Sckopke et al, 1981), as evidence for magnetic merging and the formation of twisted flux ropes of interconnected magnetosheath and magnetospheric field lines (Paschmann et al, 1982), and as quasiperiodic magnetopause motions and observation of draped northward magnetosheath magnetic field lines in the plasma depletion layer (Sibeck et al, 1990). A three-dimensional plasma analyzer SCA-1 having a relatively fast duty cycle (less than 10 s) and moderate angular and energy resolution is installed on the Interball-1/Tail Probe satellite It provides ion measurements much faster than the period of the satellite’s rotation (120 s), enabling one to study plasma evolution at magnetospheric boundaries and relevant processes. We present here a description of the instrument, show examples of data, and give preliminary explanation of observed plasma structures
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