New Perspective on Phase Space Density Analysis for Outer Radiation Belt Enhancements: The Influence of MeV Electron Injections.

Observation of growing phase space density (PSD) peak in the outer electron radiation belt has been considered evidence for local wave‐driven acceleration as a primary cause of radiation belt enhancement. However, recent studies showed that strong substorm‐associated MeV electron injections can also cause significant radiation belt enhancements on fast timescales (∼10s min). Such rapid enhancements pose challenges for determining true spatial PSD profiles. To address this, we conduct a detailed spatiotemporal analysis of electron flux and PSD during an enhancement event, using Van Allen Probes data. Our analysis reveals rapid and intermittent flux enhancements. During these rapid enhancements, inbound spacecraft observed false PSD peaks, due to spacecraft's relatively slow movement. However, we identify time intervals of stable fluxes between enhancements, enabling us to determine quasi‐stationary PSD profiles with no noticeable peaks. This study provides new insights into accurate PSD analysis, critical for understanding the mechanisms underlying radiation belt enhancements. Plain Language Summary: Radiation belt physics studies the origin and dynamics of high‐energy electrons trapped in the Earth's radiation belts. The radial profiles of these electrons' phase space density (PSD) are essential parameters for investigating their origin and dynamics. Outward‐increasing PSD profiles indicate that electrons have been transported radially (injections) from outside the radiation belt, while locally peaked profiles suggest that they were generated locally within the belt. Obtaining accurate PSD profiles is challenging due to significant temporal changes in electron flux, particularly rapid flux enhancements from injections as observed in recent studies. To examine the impact of rapid flux enhancements on PSD analysis, we closely tracked electron flux changes in space and time during an enhancement event using data from NASA's Van Allen Probes. Our results show that inbound spacecraft can observe falsely peaked PSD profiles during rapid flux enhancements, which are temporal artifacts from relatively slower spacecraft motion. By identifying time intervals of stable electron flux between enhancements, we were able to determine the true spatial PSD profiles, which overall exhibited outward‐increasing trends, consistent with injections. Our findings offer new perspective on accurately determining PSD radial profiles, which is essential for unraveling the origins of high‐energy electrons in the Earth's radiation belts. Key Points: Rapid and intermittent electron enhancement pattern significantly impacts phase space density (PSD) analysisInbound spacecraft can observe a temporal PSD peak during rapid electron enhancements driven by injectionsQuasi‐stationary time intervals between enhancements enable accurate determination of PSD radial profiles [ABSTRACT FROM AUTHOR]