Long-term variations in the relativistic (∼MeV) electrons in the Earth's radiation belt are explored to study seasonal features of the electrons. An L-shell dependence of the seasonal variations in the electrons is reported for the first time. A clear ∼6 month periodicity, representing one/two peaks per year, is identified for 1.5–6.0 MeV electron fluxes in the L shells between ∼3.0 and ∼5.0. The relativistic electron flux variation is strongest during solar cycle descending to minimum phases, with weaker/no variations during solar maximum. If two peaks per year occur, they are largely asymmetric in amplitude. The peaks essentially do not have an equinoctial dependence. Sometimes the peaks are shifted to solstices, and sometimes only one annual peak is observed. No such seasonal features are prominent for L<3.0 and L>5.0. The results imply varying solar/interplanetary drivers of the radiation belt electrons at different L shells. This has a potential impact on the modeling of the space environment. Plausible solar drivers are discussed.

中文翻译：

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地球辐射带的季节性依赖性–新见解

探索了地球辐射带中相对论（〜MeV）电子的长期变化，以研究电子的季节性特征。首次报道了电子季节性变化的L壳依赖性。在L壳层中约3.0至5.0之间的1.5–6.0 MeV电子通量中 ，明确了约6个月的周期性，代表每年一个/两个峰值。 。相对论电子通量变化在太阳周期下降到最小相位时最强，而在太阳最大时变化较弱/没有变化。如果每年出现两个高峰，则它们的幅度在很大程度上是不对称的。峰基本上不具有等电依赖性。有时高峰移至孤峰，有时仅观察到一个年度高峰。当L <3.0和L > 5.0时，没有这样的季节性特征。结果表明，在不同的L壳层，辐射带电子的太阳/行星际驱动器发生了变化。这对空间环境的建模有潜在的影响。讨论了合理的太阳能驱动器。