Longitude and temporal variations of energetic electron precipitation near the trapping boundary

Electron precipitation occurring at latitudes near the midnight trapping boundary was measured remotely with a satellite‐borne x ray imager (>21 keV). This investigation has demonstrated for the first time the repetitive mapping of precipitation at the trapping boundary with x rays. The satellite spin motion (5.5 second period) provided repeated scans of each scene during a single pass of the satellite. When the in situ electron precipitation, measured directly with a spectrometer (>68 keV) on the same satellite, was limited to a narrow region at the trapping boundary the precipitation inferred from the x rays was generally fairly uniform over a median longitude interval of at least 45°. Significant decreases of x rays at longitudes away from the satellite crossing seldom occurred, but significant increases at certain longitudes were sometimes observed. The widespread arc patterns of the precipitation have important implications for both understanding the nature of the responsible loss mechanisms and for assessing the atmospheric effects.