Statistics of the Magnetospheric Multi-Scale Observations of Energetic Particle Properties and their Relation to Diamagnetic Cavities

Encounters with the high-latitude magnetopause by the Magnetospheric Multi-Scale spacecraft allow to study the origin of high energy (>40 keV) particles in the magnetosheath which may be leaking out of the magnetosphere [Nykyri et al., 2019a, JGR]. Of particular interest are observations of energetic particles trapped in the high-latitude diamagnetic cavities, that can be formed by magnetic reconnection. The origin of these particles may have multiple sources: ionosphere, solar wind, and magnetosphere. Test particle simulations indicate that particles can be locally accelerated due to the reconnection quasi-potential if they remain trapped sufficiently long, and can be subsequently lost when magnetic field topology in the vicinity of the cavity changes (e.g. due to changes in IMF orientation or by Kelvin-helmholtz Instability (KHI)). We present a statistical analysis of high energy electron and ion observations in the diamagnetic cavities as well as global MHD simulations with test particles to determine their source and subsequent transport trajectories. We also analyze the observed magnetic fields and plasma flows to determine whether these events can be attributed to diamagnetic cavities formed by the traditional magnetic reconnection scenario near the magnetospheric cusp, or by low-latitude component reconnection, and what is the role of the high-latititude KHI in the transport of these energetic particles from the dayside diamagnetic cavities into the magnetosphere or magnetosheath.