First VIKING results: hot plasma

Abstract

In this report we present preliminary results obtained from the charged particle experiment on board the VIKING satellite. Of special interest are the very detailed measurements of the electron and ion distribution functions. This high resolution data base is expected to bring new insight into the physical processes governing the acceleration and heating of plasma at low and medium altitudes over the auroral zone and polar cap region.We present here examples from the data set showing e.g., that:– The acceleration/heating processes generating ion conics are frequently also associated with an acceleration/heating of ionospheric electrons.– Upward accelerated ionospheric electrons, usually observed as "bidirectional electron beams", can have the shape of narrow conics.– Features in the electron distribution function provide unambiguous evidence for an electrostatic acceleration process accelerating electrons downwards. Frequently, however, there are characteristics of the electron distribution function which suggest a more complex acceleration process than can be described by simple static models.Repeated injections of solar wind plasma in the cleft region are also observed. From the time dispersion characteristics of the injected plasma it is possible to determine the distance to the injection point at the dayside magnetopause. Implications of these observations are discussed.