Global Observations of the O+/H+ Ratio During Large Geomagnetic Storms

During large geomagnetic storms the fraction of magnetospheric oxygen ions increases compared to hydrogen, and is at times even becomes the dominant population. However, it is not well known how this population is energized and transported in the inner magnetosphere. Using a combination of global images from the Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission and in situ observations from the Van Allen Probes Hydrogen Oxygen Proton and Electron (HOPE) sensors, we examine how the inner magnetospheres O+/H+ changes during large storms. TWINS provides continuous global observations of medium energy (<50 keV) H and O Energetic Neutral Atoms (ENAs) from the inner magnetosphere. These ENA observations allow us to follow global changes in the composition and energy during storms. HOPE provides 20 eV-45 keV, high-spatial-resolution, in situ measurements of the inner magnetospheric source populations for the ENAs. We present these complementary (global and local) observations of the O+/H+ ratio for selected case study storms, and examine the dependence on local time and storm phase.