Solar Origin and Interplanetary Evolution of Stream Interfaces

In a Corotating Interaction Region (CIR) the stream interface is identified as a relatively sharp density drop, temperature rise, and flow shear in the solar wind, and is now generally believed to mark the boundary between solar wind which was originally slow when it left the Sun and solar wind which was originally fast. This paper summarises some important facts and open questions about the origin and nature of the boundary between fast and slow solar wind near the Sun, the evolution of stream interfaces with heliocentric distance in the inner heliosphere, and their relationship. This revised version was published online in August 2006 with corrections to the Cover Date.