Auroral emissions and particle precipitation in the noon sector

In this article air-borne optical measurements during December 1969 are compared with satellite particle measurements made earlier in 1969. The latitudinal distributions of Hβ, λ4278, and λ6300 emissions during quiet periods are observed to agree with what would be expected from the latitudinal distribution of particle precipitation during similar conditions. In particular, there is a belt 200–500 km wide (at ionospheric heights) in which the magnetosheath plasma penetrates down to low altitudes through the cusps in the dayside magnetosphere and in which both Hβ and λ6300 emissions are observed. There are brighter red arcs with green lower borders within this belt. It is suggested that these are produced by narrow regions of precipitation of slightly more energetic electrons embedded in the cusp fluxes. Poleward of this belt the flux of particles is low, and the atmospheric emissions are very weak, except for occasional narrow regions of electron precipitation (without measurable protons) and the corresponding polar-cap aurora (without the Hβ emission). In the morning sector a wide region of precipitating outer Van Allen belt electrons is observed equatorward of the cusp. A corresponding diffuse glow of λ5577 and λ4278 emissions is observed. These features are also present in the afternoon but are much weaker in intensity. Data supporting these conclusions are presented, including color all-sky photographs and photometric latitude profiles obtained from high-altitude aircraft and intensity-modulated energy-time spectrograms for particle fluxes.

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