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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Short summary
Geomagnetic activity is known to exhibit semi-annual variation with larger occurrences during equinoxes. A similar seasonal feature was reported for relativistic (∼ MeV) electrons throughout the entire outer zone radiation belt. Present work, for the first time reveals that electron fluxes increase with an ∼ 6-month periodicity in a limited L-shell only with large dependence in solar activity cycle. In addition, flux enhancements are not essentially equinoctial.
Preprints
https://doi.org/10.5194/angeo-2020-62
https://doi.org/10.5194/angeo-2020-62

  22 Sep 2020

22 Sep 2020

Review status: a revised version of this preprint is currently under review for the journal ANGEO.

Seasonal dependence of the Earth's radiation belt: new insight

Rajkumar Hajra Rajkumar Hajra
  • Indian Institute of Technology Indore, Simrol, Indore 453552, India

Abstract. Long-term variations of 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 of the electrons is revealed for the first time. A clear ~ 6-month periodicity is identified for 1.5–6.0 MeV electron fluxes in the L-shells between ~ 3.0 and ~ 5.0, representing two peaks per year. The two-peak variation is strong during solar cycle descending to minimum phases, with weaker/no variations during solar maximum. The peaks are largely asymmetric in amplitude. These are not essentially equinoctial: sometimes the peaks are shifted to solstices and sometimes one annual peak is only 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 space environment. Plausible solar drivers are discussed.

Rajkumar Hajra

 
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Rajkumar Hajra

Rajkumar Hajra

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Short summary
Geomagnetic activity is known to exhibit semi-annual variation with larger occurrences during equinoxes. A similar seasonal feature was reported for relativistic (∼ MeV) electrons throughout the entire outer zone radiation belt. Present work, for the first time reveals that electron fluxes increase with an ∼ 6-month periodicity in a limited L-shell only with large dependence in solar activity cycle. In addition, flux enhancements are not essentially equinoctial.
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