ON THE DIFFERENCES IN ELEMENT ABUNDANCES OF ENERGETIC IONS FROM COROTATING EVENTS AND FROM LARGE SOLAR EVENTS

We have examined the abundances of energetic ions accelerated from high-speed solar wind streams by shock waves formed at corotating interaction regions (CIRs) where high-speed streams overtake the lower speed solar wind. The observed element abundances appear to represent those of the high-speed solar wind, unmodified by the shock acceleration. These abundances, relative to those in the solar photosphere, are organized by the first ionization potential (FIP) of the ions in a way that is different from the FIP effect commonly used to describe differences between abundances in the solar photosphere and those in the solar corona, solar energetic particles (SEPs), and the low-speed solar wind. In contrast, the FIP effect of the ion abundances in the CIR events is characterized by a smaller amplitude of the difference between high-FIP and low-FIP ions and by elevated abundances of He, C, and S. It is likely that these differences in abundances can be understood in terms of higher temperatures and shorter time scales in the chromospheric fractionation region of coronal holes. Similar processes could also cause the enhanced C/O ratio and the strong suppression of He in the Galactic cosmic-ray sources.