Measurement of Solar and Diurnal Effects in the High Atmosphere by Artificial Satellites

Abstract

IN a previous investigation¹ atmospheric densities had been derived from the orbital elements² of the satellites 1958 β 2, 1958 α, 1958 δ and others, and reduced to the mean altitude of the perigee by means of the Kallmann–Juncosa³ model. A good correlation exists between atmospheric fluctuations and the 20-cm. solar flux curve⁴. This is apparent not only from the ‘monthly’ fluctuations⁵ but also from long-period variations extending over several months. For altitudes of 660, 350 and 210 km. the relation between density and solar flux is approximately linear for values of solar flux S between 100 and 240 × 10⁻²² W./m.² c./s. To demonstrate the effect it was necessary to separate quantitatively the suspected diurnal fluctuations and the fluctuations caused by variable solar radiation. A preliminary investigation was carried out using the geocentric angular distance perigee–Sun which had already been employed by Jacchia (see ref. 2) for comparison with the satellite data. The angular distance proved very useful so long as no separation of the diurnal and terrestrial effects was possible. One expected, however, the atmospheric density to be dependent on Δα = α_π−α_⊙, Δδ = δ_π−δ_⊙ and the geocentric latitude ψ of the perigee (where α is right ascension, δ is declination, π is perigee, ⊙ is Sun).