Equatorial and precipitating solar protons in the magnetosphere, 2. Riometer observations

The equatorial solar protons measured on ATS 1 during the January 28, 1967, solar event are used together with the ionosphere model of Potemra et al. (1969) to calculate the expected daytime 30-MHz riometer absorption. The computed absorption values compare favorably with the riometer observations at Byrd, Antarctica, located on approximately the same L shell (L=7) as ATS 1 (L=6.4). The latitude profiles measured by the polar-orbiting satellite 1963-38C show that during the decay of the event Byrd was within a latitude region where fewer protons precipitated in comparison to higher latitudes. The absorption measured at Byrd during this period was systematically lower than the absorption measured at either South Pole (L=13) or McMurdo (L=32), stations well within the polar cap. Absorption values computed from the 1963-38C proton fluxes at the latitude of Byrd compare favorably with the observed absorption at this station. Empirical linear relationships between the square root of the 2π-omnidirectional ATS 1 proton fluxes greater than some Emin and the daytime 30-MHz riometer absorptions are also studied, with an excellent correlation found for Em i n over a wide energy range.