On the extraterrestrial ring current during geomagnetic storms

Abstract

Measurements of the differential energy spectrums of protons and electrons, separately, over the energy range extending from ∼200 ev to 50 kev with a sensitive array of electrostatic analyzers borne on the earth-satellite OGO 3 reveal large temporal variations in intensities of these low-energy charged particles at low and moderate latitudes in the outer radiation zone during two moderate geomagnetic storms in late June and early July 1966. At L = 3.5 on July 9, for example, the intensities of protons (31 ≤ E ≤ 49 kev) increased by factors ≳30 over the pre-storm intensities. The peak proton (200 ev ≤ E ≤ 50 kev) energy densities at the magnetic equator for June 23 (relative magnetic quiescence), June 25 (DST(H) ≃ −30 γ), and July 9 (DST(H) ≃ −50 γ) were 9 × 10−8 erg(cm)−3 at L = 6.8, 2 × 10−7 erg(cm)−3 at L = 4.5, and 5 × 10−7 erg (cm)−3 at L = 3.3, respectively. This energy density is predominantly shared by protons in the energy range ∼3–50 kev. The total energy of these low-energy protons and electrons within the earth's magnetosphere is sufficient to account for the depression of the geomagnetic field (DST(H)) observed at the earth's surface over low and moderate latitudes; hence these charged particles may be identified as the major contributors to the storm-time extraterrestrial ring current. Electrons (200 ev ≤ E ≤ 50 kev) are found to provide approximately 25% of this storm-time ring current. The apparent mean lifetimes of low-energy protons in the outer radiation zone are in agreement with calculated lifetimes assuming charge-exchange collisions with the ambient neutral and charged constituents of the terrestrial exosphere as the predominant loss mechanism.