Statistical Study of Oxygen Ions Abundance and Spatial Distribution in the Dayside Magnetopause Boundary Layer: MMS Observations

Abstract

AbstractUsing energetic ion composition data at the dayside magnetopause measured by Magnetospheric Multiscale (MMS) satellites, we study the responses of H+, O+ density (1–40 keV), and their ratio to geomagnetic activity and solar wind conditions; their spatial distributions in the XYGSM plane for different ranges of the above parameters are presented as well. The dependencies of the H+ and O+ fluxes spatial distributions on different energy ranges are also investigated. Statistical results show that the dependencies of the H+ density on SYM‐H index, IMF By, and IMF Bz are weak, while the O+ density and its abundance (O+/H+) vary with SYM‐H index and solar wind dynamic pressure exponentially. The IMF directions not only affect the O+ density and its abundance but also play a major role in their spatial distributions. The O+ density shows duskside asymmetry under southward IMF with positive IMF By and shows dawnside asymmetry under northward IMF with negative IMF By. The influence of the dawn‐dusk IMF direction on dawn‐dusk asymmetry is significant. The positive and negative IMF By can strengthen the O+ duskside asymmetry and dawnside asymmetry when the IMF is southward and northward, respectively. Otherwise, as particle energy enhances from ~10 to ~35 keV, the H+ fluxes concentrate more on the duskside magnetopause boundary layer while the O+ fluxes dawn‐dusk asymmetry shows minor difference. This suggests that the H+ and O+ at energies below 40 keV experience different processes when they are transported to the dayside magnetopause boundary layer.