Explorer 12 observations of the temporal variations of low-energy electron intensities in the outer radiation zone during geomagnetic storms

Abstract

Large increases of electron 100 ev ≲ Ee ≲. 40 kev energy fluxes over L ≃ 2.8 to L ≃ 4.0 were observed at the onset of magnetic storms on October 1 and October 29, 1961, with instrumentation on Explorer 12. The omnidirectional energy fluxes at L = 3.5 were ∼1000 ergs(cm2 sec)−1 for these two events, the duration of these events was approximately one day, and the peak energy flux was positioned at L ≃3.0. The large enhancement of electron 100 ev ≲ Ee ≲ 40 kev energy fluxes on October 1 is coincident with large decreases of electron Ee ≳ 1.6 Mev intensities and with increases of electron 40 kev ≲ Ee ≲ 100 kev intensities in the outer radiation zone. Although no spectral information concerning the electron 100 ev ≈ Ee ≤ 40 kev fluxes is available, estimates of the decrease of the magnetic field on the surface of the earth at the magnetic equator for monoenergetic electron intensities corresponding to the observed energy fluxes are ∼60 γ for Ee = 500 ev and ∼30γ for Ee = 2 kev during the main phase of the magnetic storm. The observations reported here suggest that these electrons form a ring current centered at ∼3 RE, which is responsible for some fraction of the main phase and the rapid-decay component DR1 of magnetic storms. An upper limit on the increases of the proton Ep≳ 400 ev energy fluxes is ∼100 ergs (cm2 sec)−1 at L∼3 during the main phases of these two magnetic storms, an upper limit that is not low enough to eliminate a low-energy proton ring current of similar or greater magnitude when compared with the above low-energy electron ring current.