Fast moving plasma structures in the distant magnetotail

Abstract

We report in this paper for the first time the detailed time behavior of the intensities and the angular distributions of energetic protons and electrons in the distant magnetotail of the earth at ∼220 R E and ∼110 R E . The data have been obtained by the Max‐Planck‐Institut/University of Maryland sensor system on ISEE 3 during the spacecraft’s first deep tail passage. Three energetic particle bursts are studied in detail. At the beginning of these bursts we first observe streaming electrons at an energy of 75–115 keV. These are followed after several minutes by anisotropic protons. The protons exhibit an energy dispersion with higher energy protons (∼120 keV) appearing before lower energy (∼32 keV) protons. In two of the three cases the streaming electron distributions are followed after 8–15 min by an isotropic electron distribution. At the rear side of the bursts the time dispersion effects are not seen in reverse order. Also, no gradient anisotropy effects are observed in the beginning of the proton streaming. We suggest that the satellite encounters detached plasma structures evidenced by the isotropic electrons. These structures, probably plasmoids, move with high velocities (∼800 km/s) down the tail. The energetic electrons and protons stream ahead of these fast tailward moving plasma structures, which leads to the various time dispersion effects. This allows, in principle, a determination of the source distance from the satellite.