MIRRORING OF FAST SOLAR-FLARE ELECTRONS ON A DOWNSTREAM COROTATING INTERACTION REGION

We discuss an example of confinement of fast solar electrons by a disc rete solar wind-interplanetary magnetic field structure on February 22 , 1991. The structure is about 190,000 km in width and is clearly defi ned by changes in the direction of the magnetic field at the Ulysses s pacecraft. This structure carries electrons moving toward the Sun as w ell as away from the Sun. A loss cone in the angular distribution of t he fast electrons shows that mirroring, presumably magnetic, tal;es pl ace downstream from the spacecraft. Following passage of this narrow s tructure, the return flux vanishes for 21 mill after which time the mi rroring resumes and persists for several hours. We identify the enhanc ed magnetic field region lying downstream from the Ulysses spacecraft that is responsible for the mirroring to be a corotating stream intera ction region. Backstreaming suprathermal electron measurements by the Los Alamos National Laboratory plasma experiment on the Ulysses spacec raft support this interpretation.