COLD ION STREAMS CONSISTING OF DOUBLE PROTON POPULATIONS AND SINGLY CHARGED OXYGEN OBSERVED AT THE DISTANT MAGNETOPAUSE BY GEOTAIL - A CASE-STUDY

The Geotail plasma and magnetic field observations reveal that multipl e ion streams with different energies coexist at the magnetopause sepa rating the magnetosheath and the lobe/mantle in the distant magnetotai l at (-187, -23, -2) R(E) in the GSM coordinates. The ion streams some times consist of three components flowing tailward. On the basis of Ex B drift analysis, we have identified that two of the three streams are protons, while the residual one of the highest energy (>7 keV/q) cons ists of O+. The direction of the perpendicular velocities of these ion components is toward the magnetosheath from the lobe/mantle. The high er-energy (-2 keV/q) proton component is detected only at the magnetop ause, while the other two components (the lower-energy (<1 keV/q) prot ons and O+) can also be observed in the lobe/mantle. In the lobe/mantl e, the bulk velocity of the O+ flow is always nearly equal to that of the lower-energy proton stream, In O+ component cannot be recognized c learly. In the magnetopause current layer, the lower-energy proton com ponent is significantly accelerated in the direction perpendicular to the magnetic field due to electric field enhancement, whereas the para llel speeds of the higher-energy protons change according to the energ ization rate in the current layer, The temperature of the higher-energ y proton stream is generally 50-100 eV approximately twice as large as that of the lower-energy proton stream in the lobe/mantle and slightl y higher than that of protons in the magnetosheath. These signatures o f multiple ion streams are discussed in terms of magnetic field reconn ection at the lobe/mantle magnetopause.