Abstract
Abstract. During moderate magnetic storms, an electron channel (300–1100 keV) of the NOAA satellite has shown sudden electron flux enhancements in the inner radiation belt. After examinating the possibility of contamination by different energetic particles, we conclude that these electron flux enhancements are reliable enough to be considered as natural phenomena, at least for the cases of small to moderate magnetic storms. Here, we define small and moderate storms to be those in which the minimum Dst ranges between −30 and −100 nT. The electron flux enhancements appear with over one order of magnitude at L~2 during these storms. The enhancement is not accompanied by any transport of electron flux from the outer belt. Statistical analysis shows that these phenomena have a duration of approximately 1 day during the period, starting with the main phase to the early recovery phase of the storms. The flux enhancement shows a dawn-dusk asymmetry; the amount of increased flux is larger in the dusk side. We suggest that this phenomenon could not be caused by the radial diffusion but would be due to pitch-angle scattering at the magnetic equator. The inner belt is not in a stationary state, as was previously believed, but is variable in response to the magnetic activity.
Highlights
The variability of energetic particles in the Earth’s radiation belts has been studied in order to understand particle acceleration and loss processes and their relationship to magnetospheric disturbances
The most significant point is that the electron flux at L=2 increased by more than one order of magnitude during the main phase before the flux increase in the outer belt
It should be noted that the inner belt enhancement was separated from the outer belt by the distinct slot region
Summary
The variability of energetic particles in the Earth’s radiation belts has been studied in order to understand particle acceleration and loss processes and their relationship to magnetospheric disturbances (see the review for electron radiation belts by Friedel et al, 2002, and the references therein). By using data from the NOAA satellite, Kikuchi and Evans (1989) showed that a >30-keV electron flux at the lower L (∼1.3) exhibited a sudden enhancement during a magnetic storm. Morioka et al (2001) and Miyoshi et al (2002) reported that a 300-keV electron flux enhancement in the inner belt (L∼2) was synchronized with the onset of the outer belt electron decrease during some magnetic storms. A polar orbiting low-altitude satellite such as NOAA is appropriate for observing flux distributions and their dynamics over a wide range of L with high time resolution because it permits a detailed comparison between the outer and inner radiation belts within time scales of the development of storms. The electrons of the 90◦ sensor are in the drift loss cone (Blake et al, 2001)
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