The solar origin of corotating interaction regions and their formation in the inner heliosphere - Report of Working Group 1

Corotating Interaction Regions (CIRs) form as a consequence of the compress ion of the solar wind at the interface between fast speed streams and slow streams. Dynamic interaction of solar wind streams is a general feature of the heliospheric medium; when the sources of the solar wind streams are rel atively stable, the interaction regions form a pattern which corotates with the Sun. The regions of origin of the high speed solar wind streams have b een clearly identified as the coronal holes with their open magnetic field structures. The origin of the slow speed solar wind is less clear; slow str eams may well originate from a range of coronal configurations adjacent to, or above magnetically closed structures. This article addresses the corona l origin of the stable pattern of solar wind streams which leads to the for mation of CIRs. In particular, coronal models based on photospheric measure ments are reviewed; we also examine the observations of kinematic and compo sitional solar wind features at 1 AU, their appearance in the stream interf aces (SIs) of CIRs, and their relationship to the structure of the solar su rface and the inner corona; finally we summarise the Helios observations in the inner heliosphere of CIRs and their precursors to give a link between the optical observations on their solar origin and the in-situ plasma obser vations at 1 AU after their formation. The most important question that rem ains to be answered concerning the solar origin of CIRs is related to the o rigin and morphology of the slow solar wind.