In the present declining phase of the solar cycle, corotating interaction regions (CIRs) have once again become more prevalent. Since the launch of the two STEREO spacecraft in October 2006, at least 5 significant particle enhancements due to CIRs have been observed at 1 AU. The Low Energy Telescope (LET) on each STEREO spacecraft has been operating since mid-November 2006. This instrument is capable of measuring elemental composition and spectra for particles from H to Ni (and beyond) from ~2 to ~50 MeV/nucleon, depending on species, and in addition provides anisotropy information for 6 different species or element groups. Another STEREO instrument, the Suprathermal Ion Telescope (SIT), measures ion composition from ~0.05 to 5 MeV/nucleon. Using data from these STEREO instruments, supplemented with measurements from ULEIS and SIS on ACE, we obtain preliminary results on the spectra, composition, and anisotropy of these CIR events.

This work was supported by NASA under grants NAS5-03131 and NAG5-12929.

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 1 (SH), pages 375-378