Observation and Interpretation of Energetic Neutral Hydrogen Atoms from the December 5, 2006 Solar Flare

Although solar energetic particle (SEP) activity has been at a minimum for the last few years, significant particle enhancements due to corotating interaction regions (CIRs) have regularly appeared at 1 AU, providing an ideal opportunity to study CIR particles without SEP contamination. Observations of CIR time profiles from the two STEREO spacecraft commonly show delays that are often roughly as expected from the corotation time lag between the two spacecraft. However, in many cases different features seen at Ahead and Behind may suggest that transient disturbances in the solar wind alter connection to or transport from the shock, or that temporal changes occur in the CIR shock itself. We present CIR observations from STEREO and ACE at energies from ~2-10 MeV/nucleon and examine the evolution of CIR time profiles as a function of spacecraft separation in longitude, radius, and heliographic latitude