Simultaneous Observations of Electron Phase Space Density Variations in the Geostationary Orbit by GK2A, GOES‐16, and GOES‐17

Abstract This study presents simultaneous measurements of electron phase space density (PSD) gradients in geostationary orbit using data from GK2A, GOES‐16, and GOES‐17. By leveraging a three‐satellite configuration, we provide statistical results of PSD gradient estimation in invariant coordinates. The analysis examines spatiotemporal PSD variations under both geomagnetically quiet and disturbed conditions. During quiet times, positive PSD gradients in the third invariant ( L* ) occur more frequently at low (≲500 MeV/G) and small (≲0.5 ), consistent with radial diffusion. In contrast, geomagnetic disturbances often produce negative gradients at high () and large (0.5), suggesting enhanced losses such as magnetopause shadowing and pitch‐angle scattering, coupled with local acceleration inside the geostationary orbits. In addition to purely positive or negative gradients, the three‐satellite observation reveals profiles of localized PSD maxima and minima, indicative of spatially confined source and sink processes. Statistical analysis further shows that these complex PSD profiles constitute a major fraction of the observed PSD variation near the geostationary orbit. These findings underscore the energy‐ and pitch‐angle‐dependent dynamics of radiation belt electrons and demonstrate the importance of multi‐point geostationary observations for understanding coupled source‐loss processes in the outer radiation belt.