Equinox and solstice averages of magnetospheric relativistic electrons: Strong semiannual modulation of fluxes

Data from SAMPEX, POLAR, and other spacecraft have previously shown that high energy electrons (E ≳ 1 MeV) vary in a remarkably coherent way throughout the entire outer radiation zone of the Earth (2.5 ≲ L ≲ 6.5). Such data have been used to perform analysis of the flux variations of relativistic electrons throughout the outer Van Allen zone. This talk reports similar analyses of Van Allen Probes data from the REPT sensor system from 2012 to 2019. Averages are performed for monthly intervals centered on the spring and fall equinoxes and on the winter and summer solstices. Modulation is deonstrated such that equinoctial fluxes of electrons are larger than the solstitial fluxes by large factors based upon a superposed epoch analysis. These semiannual modulations of relativistic electron fluxes are compared with concurrent solar wind data. Results are also examined in terms of prior models of geomagnetic activity acceleration processes.