Geophysical Research Letters

Magnetic storm of September 4, 1984: A synthesis of ring current spectra and energy densities measured with AMPTE/CCE



Comprehensive energy (a few eV ≲ E ≲ 5 MeV), charge state, and mass coverage of the particle instrumentation on the AMPTE Charge Composition Explorer (CCE) satellite, together with field and wave instruments, has made possible compositional studies of equatorial distributions of ring current ions during the magnetic storm of September 4, 1984. Examination of ion spectra at L ≃ 4 on September 5 in the local evening sector (∼ 1700 MLT), where the maximum magnetic field depression and ground-based Dst were seen, shows that the energy density was dominated by protons, with oxygen ions contributing ∼ 27% at the peak (∼ 150 keV), while helium ions contributed ≲ 2%. The energy density versus L profile shows that the majority of the ring current resided in the range 3.2 ≲ L ≲ 4. Ion spectra on September 6 during the recovery phase of the storm show that oxygen ion intensities at ≳ 20 keV had decreased markedly and the ring current energy density at this time was provided mostly by protons.