Corotating interaction regions in the outer heliosphere - Report of Working Group 4

We discuss the structure and evolution of CIRs and their successors in the outer heliosphere. These structures undergo significant evolution as they a re convected to greater heliocentric distances. A progression of different types of structure are observed at increasing distance from the Sun. Simila r structures are observed at similar heliocentric distance at different por tions of the solar cycle. CIRs and their successors are associated with man y important physical processes in the outer heliosphere. We discuss the rel ationship between these structures and recurrent phenomena such as cosmic r ay variations, and review some of the associated theoretical models on the role of corotating structures and global merged interaction regions (GMIRs) in global cosmic ray modulation. We also discuss some outstanding question s related to the origin of non-dispersive quasi-periodic particle enhanceme nts associated with CIRs and their successors in the outer heliosphere.