Energetic particle signatures of a corotating interaction region from a high latitude coronal hole: SOHO, wind and Ulysses observations Original Research Article

In mid 1996 the Comprehensive Suprathermal and Energetic Particle Analyser (COSTEP) onboard the Solar and Heliospheric Observatory, at 1 AU in the ecliptic plane, detected recurrent periods of enhanced MeV ions in association with a corotating interaction region (CIR). Measurements of energetic ions from the Cosmic Ray and Solar Particle Instrument/Low Energy Telescope (COSPIN/LET) onboard Ulysses taken at 5 AU, at mid-northern heliographic latitudes, showed that Ulysses encountered recurrent particle events during the same time period. We used the solar wind speeds observed at both locations to estimate the corresponding solar source longitudes of the particle events. These longitudes are related to warps of the Sunʹs large high latitude northern coronal hole boundaries observed by SOHOʹs Extreme Ultraviolet Imaging Telescope (EIT). The findings are supported by threedimensional magnetohydrodynamic (MHD) calculations of the footpoint positions of the magnetic field lines at both spacecraft. The observations suggest that close to the Sun a superradial expansion of the fast solar wind from the Sunʹs high latitude northern coronal hole down to ecliptic latitudes is present.