Statistical Analysis of Storm‐Time O ⁺ Outflows as Observed by the Van Allen Probes

Abstract The outflow of low‐energy ions into inner magnetosphere is a key contributor to the warm plasma cloak, and O + torus, which can also contribute to storm time ring current particularly after local acceleration. Although outflows are well observed, their source and transport in the inner magnetosphere remain unclear. Using Helium Oxygen Proton and Electron mass spectrometer data from the Van Allen Probes, we systematically examine outflows during geomagnetic storms. We developed an automated event identification method to detect outflows, estimate onset times, and record occurrence details. With this event set, we performed a statistical analysis of occurrence characteristics and storm phase dependence, separately for outflows parallel and anti‐parallel to the magnetic field. Our findings show: (a) outflows are mostly detected off the magnetic equator; (b) with the understanding that the parallel outflows are from the Southern Hemisphere, while anti‐parallel from the Northern Hemisphere, we observed more events in the hemisphere within which the source of O + outflow lies; (c) the peak of the occurrence rate in MLT is derived at mid‐night with skewing toward dawn; (d) during the main phase of the storms, outflows events are concentrated at post‐midnight and dawn. Decrease in the occurrence rate is observed in the recovery phase. Hemispheric and dawn‐dusk asymmetries are evident in the event distribution patterns; (e) a preference for outflows from the summer hemisphere. These results offer new insights into nightside, low‐energy outflows. Our large event data set enables us to explore the sources of energization and their transport better.