A Search for Compositional Differences in Slow Solar Wind at the Leading and Trailing Edges of Stream Interfaces

Abstract

The elemental and ionic composition of the slow (∼400 km/s) solar wind (SW) differs from that of the fast (>600 km/s) SW streams. In particular, the first ionization potential (FIP) effect and the O7/O6 ratios are higher in the slow SW than in the fast SW. While this fundamental difference between fast and slow SW has long been appreciated, there has been no reason to expect or effort to search for systematic variations within given fast or slow SW streams. If present, however, such systematic variations could be diagnostic of the solar processes at the sources of the SW. We suggest two reasons to expect compositional differences between leading and trailing edges of slow SW streams. After selecting two long‐lived fast SW streams from 2005 and 2006 and determining their slow‐fast (SF) and fast‐slow (FS) stream interfaces (SIs), ACE SWICS (version 3) compositional data were obtained for the 1‐day periods of the preceding SF and following FS slow SW streams. The statistics were limited, but no compositional differences between the preceding and following slow SW regions were found for either stream sequence.