Meeting abstract

AGU Fall Meeting, San Francisco, 8-12 December 1997

Abstract: The Ulysses spacecraft encountered several flux enhancements with an approximate 26-day periodicity associated with corotating interaction regions (CIRs) during the period June 1992 to June 1994. This interval corresponds to Ulysses sampling a range of southerly latitudes, following a trajectory where the spacecraft moved from approximately 11°S to 66°S of the ecliptic plane and from approximately 5 AU to 3 AU from the Sun. During this interval we derive anisotropies present in the 1.75 MeV proton fluxes measured by the Anisotropy Telescopes instrument as part of the COSPIN consortium. The anisotropies generally have components along and transverse to the magnetic field in the spacecraft frame. In order to derive the anisotropies due to particle streaming we transform to the solar wind frame by subtracting the Compton-Getting anisotropy. In the solar wind frame the field-perpendicular components of the anisotropy are effectively zero while the parallel components exhibit significant contributions either aligned or anti-aligned with the magnetic field. At latitudes where magnetic sector boundaries are no longer observed (>30°S), examination of the field parallel component of the anisotropy reveals that particle streaming away from many CIR related shocks is consistent with shock acceleration. At lower latitudes, however, in the vicinity of magnetic sector boundaries, we observe that the flow directions of the particles are greatly influenced by magnetic sector boundary crossings with only a local modulation of the anisotropy near the CIR related shock, although often consistent with shock acceleration. Furthermore, we have been able to identify various flow interfaces within a number of CIRs and have also observed some changes in the flow that are seemingly unrelated to the magnetic field structure.