The Coronal Source Regions of Solar Wind Suprathermal Electrons at 0.1-200 keV

We present a statistical study of solar wind suprathermal (strahl, halo and superhalo) electrons and their possible coronal source regions, using Wind/3DP, ACE/SWEPAM, ACE/SWICS, SOHO/EIT and STEREO/SECCHI measurements from 1998 to 2014, by comparing their in situ properties at 1 au (e.g., power-law spectral index, number density) and the locations of their possible coronal source regions in the solar atmosphere. According to Zhao et al. (2017), the coronal source regions are classified into four types: active region (AR), quiet Sun (QS), coronal hole (CH), and helmet-streamer associated region (HS), based on the proximity of the back-mapped footpoints at 1 Rs solar surface to coronal structures in the EUV Carrington images. We find that superhalo electrons from QS generally appear to have a smaller power-law spectral index than those from AR, while superhalo electrons from different regions have a similar density. For strahl electrons, QS-strhal and CH-strahl generally appear to have a larger kappa index than AR-strahl and HS-strahl, while QS-strahl appears to have a smaller density than AR-strahl. Halo electrons generally show the same relation with their source regions as strahl electrons, but halo electrons have similar densities for all four source regions. Furthermore, superhalo electrons show no obvious correlation with the O7+/O6+ ratio, while the kappa index of strahl/halo electrons is negatively correlated with the O7+/O6+ ratio. Using these results, we will discuss the formation of strahl, halo and superhalo electrons in solar wind.