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The plasmasphere accounts for the majority of the mass of Earth's magnetosphere and contains most of the cold ion (1 eV) population. The plasmasphere is extremely dynamic, undergoing a constant cycle of erosion and refilling. In this paper we perform a statistical study of erosion and refilling rates using 6 years of data from the Van Allen Probes from the beginning of 2013 through the end of 2018. Using in‐situ density measurements derived from the upper hybrid resonance line, we create global maps of the erosion and refilling rates over a wide range of L shells and local times. Sorting the data by L shell, magnetic local time, and distance to the plasmapause, we characterize the absolute and relative rates of erosion and refilling during a variety of geomagnetic conditions. We also examine three case studies of geomagnetic storms and compare their density evolutions during the recovery period. Our results are in agreement with refilling rates found by previous statistical studies using different methods, but somewhat lower than many of the case studies reported. We find median erosion rates of 164, 83, and 43 cm−3/day and refilling rates of 87, 42, and 27 cm−3/day at L = 3, 4 and 5, respectively when Kp ≤ ${\le} $ 3. We also find little local time dependence for both erosion and refilling rates. Plain Language Summary: The plasmasphere is the innermost region of Earth's magnetosphere, and accounts for the majority the magnetosphere's mass. During a geomagnetic storm, the plasmasphere loses mass in process called erosion where plasma is transported toward the sun until it is lost from the magnetosphere. Following the storm, material from the ionosphere slowly refills the plasmasphere in a matter of weeks. In this paper we study average erosion and refilling rates using data from the Van Allen Probes during the years 2013–2018. We create global maps of the erosion and refilling rates over a wide range of longitudes and distances to Earth. We characterize both the absolute and relative rates of erosion and refilling during storms of varying intensities. We also examine three case studies of geomagnetic storms and compare their density evolutions throughout these events. Our results are in agreement with refilling rates found by previous statistical studies, but somewhat lower than many of the case studies reported. At locations of 3, 4, and 5 Earth radii away, we find median refilling rates of 87, 42, and 27 cm−3/day for storms of the lowest intensity. We also find that the erosion and refilling rates are roughly the same for the dawn, day, dusk, and night sides of the planet. Key Points: We perform a statistical study of erosion and refilling rates in the plasmasphere over L shell, local time, and geomagnetic conditionsWe present three case studies which all show similar density evolutions during the recovery periodThe percent rate of change erosion rates are well sorted by distance to the plasmapause, while refilling rates are better sorted by L shell [ABSTRACT FROM AUTHOR]

Relativistic electron precipitation (REP) refers to the release of high‐energy electrons initially trapped in the outer radiation belt, which then precipitate into Earth's upper atmosphere, contributing significantly to the rapid depletion of radiation belt electron flux. This study presents a statistical analysis of REP observations collected by the Calorimetric Electron Telescope (CALET) experiment aboard the International Space Station from 2015 to the present day. Specifically, the analysis utilizes count rates acquired from the two top scintillators constituting the top charge detector, each sensitive to electrons with energies above 1.5 and 3.4 MeV, respectively. Analysis of CALET data reveals a previously unreported semi‐annual variation in the occurrence of REP events. REP periodicities resemble those observed for trapped electron fluxes in the outer belt. Furthermore, their amplitude follows the overall trend of solar wind high‐speed streams and the solar activity. Plain Language Summary: Relativistic electron precipitation (REP) refers to the release, toward the upper atmosphere, of high energy electrons initially trapped in a torus shaped region around Earth known as the outer Van Allen radiation belt. REP is relevant as it contributes to the fast depletion of the electrons from this region. This study presents a statistical analysis of the REP observations made by the Calorimetric Electron Telescope (CALET) experiment on board the International Space Station (2015–present). Data from CALET experiment reveals a previously unreported 6‐month periodicity similar to those observed for high energy electrons in the outer belt. Key Points: Semi‐annual variation of relativistic electron precipitation (REP) have been observed for the first timeReported periodicities have been compared with those characterizing the outer belt electron fluxesThe temporal variation in the REP and the trapped fluxes were found to be in strong correlation [ABSTRACT FROM AUTHOR]