REFLECTED SOLAR-WIND IONS AND DOWNWARD ACCELERATED IONOSPHERIC IONS DURING THE JANUARY 1997 MAGNETIC CLOUD EVENT

On January 11, 1997, at 03:40:00 UT, while Polar was traveling up the dusk flank toward apogee, two ion instruments, TIDE and TIMAS, detecte d upflowing H+ with an energy/pitch-angle dispersion resembling an ion ospheric reflection of freshly injected solar wind ions. In the same r egion of space, TIDE and TIMAS observed cold beams of O+ and H+ travel ing down the field line with equal bulk velocities. We interpret these ion signatures as concurrent observations of mirrored solar wind ions and downward accelerated ionospheric ions. By 03:42:00, an energy/pit ch-angle dispersion of downward moving ions at very low energies was c learly evident in the TIDE data. This additional signature is interpre ted as an indication of reconnection on the same field line in the sou thern hemisphere. We explain this unique combination of plasma distrib utions in terms of high-latitude reconnection and magnetic field line convection during northward-IMF conditions associated with the January 1997 magnetic cloud event.