Plasma observations in the magnetotail

Through the analysis of data returned from the three Rice Suprathermal Ion Detectors information on the particle regimes present in the geomagnetic tail has been obtained at lunar distances. The existence of two distinct particle populations is distinguished and many of their spatial and plasma characteristics are quantified. The first region is the plasma sheet. At lunar distance it displays an average integrated flux in the ion component of the plasma of approximately 106 ions cm-2s-1sr-1 and an ion energy density of 300 to 400 eV cm-3. Many cases of thinning of the plasma sheet and associated antisunward flow have been observed and cases of apparent double streaming in the plasma sheet have also been noted. The second region consists of cold plasma flowing antisunward along the ordered magnetic field lines of the lobes. This plasma is found across the entire tail in the Ysub(sm) direction and is often the most spatially dominant plasma region seen in the tail at lunar distance. Since this plasma is associated with the tail lobe region and appears at times to occupy much of the tail region exterior to the plasma sheet the phenomenon at lunar distance is called the 'lobe plasma'. This paper concentrates on a description of the lobe plasma. (Auth.)