Energetic electron flux behavior at low L-shells and its relation to the South Atlantic Anomaly

Abstract

Here we study energetic electron fluxes in the inner radiation belt ( L < 2 ) , especially within the South Atlantic Anomaly (SAA) region during a period of a few months using data from the low-altitude NOAA-15 and 16 satellites. Observations by these two spacecraft can yield long-term measurements of energetic electron fluxes at four different local time sectors. We discuss the time development as well as local time and longitude dependence of energetic electron fluxes around the magnetic equator at L < 2 inside and outside of the SAA region. In particular, we concentrate on the observed local time dependence of trapped and precipitating fluxes inside the SAA region and the observed interesting differences between the trapped and precipitating components. Our observations show that there is a strong and stable dawn–dusk asymmetry in the precipitating electron flux (fluxes higher in the dawn) inside the SAA present at all times. Trapped electron fluxes inside the SAA exhibit a clear local time dependence where the fluxes are maximum at night side and decrease towards east. We have suggested an explanation for these features in terms of inward radial transport of electrons mainly in the night side and wave–particle interactions that could cause the dawn–dusk asymmetry in precipitation.