Spatial distribution of relativistic electron precipitation during a radiation belt depletion event

Abstract

We present observations from the NOAA‐15 MEPED telescopes during a radiation belt depletion event on January 19–20, 2000 to investigate the spatial extent of electron precipitation during this interval. Precipitation mapped to the equatorial plane was confined to radial distances less than ∼6.5 Earth radii, indicating that precipitation was not the direct cause of the decrease in trapped flux observed by GOES. We found an enhanced day–night magnetic field asymmetry during the event, suggesting that magnetopause losses may have been responsible. Precipitation at lower L‐values was observed by POES on the dusk passes (18:30–21:00 MLT), but not on the dawn passes, and was observed in conjugate hemispheres. These observations suggest that both precipitation and magnetopause losses were acting during this flux depletion event.