Spatial and temporal variations of CIRs: Multi-point observations by STEREO

In the absence of solar activity, Co-rotating Interaction Regions (CIRs) are a prevailing source of energetic ions observed near 1 AU. The combination of observations by near-Earth space observatories and the twin STEREO spacecraft offers an excellent platform for multi-point studies of CIRs. The analysis of CIR events during Carrington rotations 2067-2082 provides evidence that CIR-associated energetic ions frequently show significant differences, particularly at sub-MeV energies. We found discrepancies in the structures observed by different spacecraft which cannot always be attributed to the latitudinal separation or to changes in the coronal hole which generates the high-speed stream. We present several cases where these differences are linked to the presence of Interplanetary Corona! Mass Ejections (ICMEs) or small-scale interplanetary transients in the vicinity of or embedded within the CIR. Evidence of the possible role of ICME-CIR interactions as sources of temporal variations in the CIR-associated ion increases are presented and discussed. (C) 2010 Elsevier Ltd. All rights reserved.