Magnetospheric ions and electrons in the distant magnetoshearth at approx.50 R/sub E/ and approx.180 R/sub E/: ISEE-3 observations

We have analyzed energetic electron (75-115 keV) and proton (approx.30 KeV) measurements at the dawn side of the distant magnetosheath at approx.50 R/sub E/ and approx.180 R/sub E/. The data have been obtained during the recent ISEE-3 Geotail Mission. At approx.50 R/sub E/ electronis and protons occur almost simultaneousy in bursts of approx.2 min duration. The electrons stream intensely away from the general magnetopause positions along the magnetic field line. The proton angular distributions exhibit a large parallel anisotropy that is symmetric with respect to the magnetic field in the plasma frame of reference. At approx.180 R/sub E/ almost no electrons have been so far observed above the threshold of our detector. The protons are isotropic in the plasma frame. The observations are discussed in terms of a possible model where magnosheath flux tubes are connected to the tail magnetic field so that the magnetospheric particles can leak out. At approx. 50R/sub E/ propagation to the spacecraft is believed to be scatter-free; after reaching approx.200 R/sub E/ the particles have resided long enough in the magnetosheath so that they are then coupled to the magnetosheath flow via pitch angle scattering