Solar Fast‐Wind Regions as Sources of Shock Energetic Particle Production

Abstract

If the production of solar energetic particles (SEPs) near the Sun is due to shocks driven by coronal mass ejections (CMEs), then two factors might favor SEP acceleration in slow rather than fast solar wind streams. The first is that both the MHD fast-mode and solar wind flow speeds are higher in the fast-wind streams. The second is that shock seed populations in the fast-wind streams consist of weak suprathermal ion tails with soft spectra. An earlier study used observed fast west-limb or halo CMEs and solar wind O+7/O+6 ratios to compare associated SEP events and fast CMEs in fast wind with those in slow wind. Properties of the few fast CMEs in fast-wind regions suggested a bias in terms of associated SEP event size and/or CME speed against shock production of SEPs in fast-wind regions. Here the previous 1998-2000 study is expanded through 2002. The results of the much larger event sample now show no significant bias against SEP production in fast-wind regions. We discuss the implications of this result for shock seed populations and for shock propagation in coronal fast-wind regions.