Introduction to the Akebono (EXOS-D) Satellite Observations
J. Geomag. Geoelectr., 42, 367-370, 1990 Introduction to the Akebono (EXOS-D) Satellite Observations By studies during the last decade of the 1970s, it has become clear that auroral particles are not directly injected from the tail region of the magnetosphere butthat there are instead two steps involved in the acceleration mechanism. The first step of the energization process occurs in the tail region of the magnetosphere while the second is found in the spatial region where the electric field is developed in a direction parallel to the earth's magnetic field. It is believed that the region of this electric fieldexists between a range of altitude of 3,000 km to 20,000km, centering around 6,000km, on fieldlines connected to the polar ionosphere. Although the general features of these acceleration processes have been identified based on previous satellite observations, there still are basic questions that remain unsolved about the physics of the acceleration region. i) What is the initial causative agent for the formation of the acceleration region? Is it induced by fast plasma injection, high energy electrons, or by magnetic field as original currents? ii) Are the particles accelerated by an electrostatic shock, a double layer, or growing large amplitude waves? iii) How is the development of the regions of acceleration related to the occurrence of magnetospheric disturbances, called substorms? The EXOS-D satellite was designed to seek solutions to these questions by conducting direct observations of the particle acceleration regions above the auroral region, with eight scientific instruments: a) Electric field detector (EFD), b) Magnetic field detector (MGF), c) Very low frequency plasma wave detectors (VLF), d) Plasma wave detectors in high frequency range and sounder (PWS), e) Low energy particle spectra analyzer (LEP), f) Suprathermal mass spectrometer (SMS), g) Temperature and energy distribution of plasma (TED), h) Auroral television camera (ATV).
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