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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. 

Abstract Shocks in collisionless astrophysical plasmas redistribute some of the incident flow energy into both thermal and non‐thermal energy. Quantifying the partition of that energy amongst various particle species or their sub‐populations, and electromagnetic energy, represents a fundamental goal of shock physics. It embodies the role of the equation of state for the system. Here we apply a framework to assess all the incident and downstream energy fluxes at a crossing of Earth's bow shock for which the upstream magnetic field was roughly aligned with the shock normal direction. Such quasi‐parallel shocks are known to be non‐steady and to produce significant populations of suprathermal particles. We quantify the evolution of all the important carriers of energy flux through the shock region. We sub‐divide the proton population into thermal, suprathermal, and energetic components in order to investigate the shock's efficiency in energizing the nonthermal particles. While the largest energy fluxes are found in the incident proton ram energy and downstream proton thermal enthalpy fluxes, a significant suprathermal population pervades the regions both up‐ and downstream. We also evaluate the energy fluxes attributable to fluctuations in the fluid and field parameters. 

The current state of the art thermal particle measurements in the solar wind are insufficient to address many long standing, fundamental physical processes. The solar wind is a weakly collisional ionized gas experiencing collective effects due to long-range electromagnetic forces. Unlike a collisionally mediated fluid like Earth’s atmosphere, the solar wind is not in thermodynamic or thermal equilibrium. For that reason, the solar wind exhibits multiple particle populations for each particle species. We can mostly resolve the three major electron populations (e.g., core, halo, strahl, and superhalo) in the solar wind. For the ions, we can sometimes separate the proton core from a secondary proton beam and heavier ion species like alpha-particles. However, as the solar wind becomes cold or hot, our ability to separate these becomes more difficult. Instrumental limitations have prevented us from properly resolving features within each ion population. This destroys our ability to properly examine energy budgets across transient, discontinuous phenomena (e.g., shock waves) and the evolution of the velocity distribution functions. Herein we illustrate both the limitations of current instrumentation and why higher resolutions are necessary to properly address the fundamental kinetic physics of the solar wind. This is accomplished by directly comparing to some current solar wind observations with calculations of velocity moments to illustrate the inaccuracy and incompleteness of poor resolution data. 

Abstract We analyze a magnetotail reconnection onset event on 3 July 2017 that was observed under otherwise quiescent magnetospheric conditions by a fortuitous conjunction of six space and ground‐based observatories. The study investigates the large‐scale coupling of the solar wind–magnetosphere system that precipitated the onset of the magnetotail reconnection, focusing on the processes that thinned and stretched the cross‐tail current layer in the absence of significant flux loading during a 2‐hr‐long preconditioning phase. It is demonstrated with data in the (a) upstream solar wind, (b) at the low‐latitude magnetopause, (c) in the high‐latitude polar cap, and (d) in the magnetotail that the typical picture of solar wind‐driven current sheet thinning via flux loading does not appear relevant for this particular event. We find that the current sheet thinning was, instead, initiated by a transient solar wind pressure pulse and that the current sheet thinning continued even as the magnetotail and solar wind pressures decreased. We suggest that field line curvature‐induced scattering (observed by magnetospheric multiscale) and precipitation (observed by Defense Meteorological Satellite Program) of high‐energy thermal protons may have evacuated plasma sheet thermal energy, which may require a thinning of the plasma sheet to preserve pressure equilibrium with the solar wind.