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Lyman α scattering in the Earth's hydrogen geocorona: 3. The extrageocoronal contribution

1964; American Geophysical Union; Volume: 69; Issue: 7 Linguagem: Inglês

10.1029/jz069i007p01301

2156-2202

T. M. Donahue,

Calibration and Measurement Techniques

A reanalysis of the high-altitude Lyman α experiment of Chubb et al. which measured the altitude variation of Lyman α brightness between 500 and 1100 km shows that the results are not inconsistent with as many as 15 × 1012 atoms/cm2 above 120 km. The altitude variation can be interpreted in terms of 0.7 × 10−3 erg/cm2 sec ster in a broad line originating outside the geocorona and 1.5 × 10−3 erg/cm2 sec ster from multiple scattering at 120 km. The extrageocoronal component is the same as that called for by the absorption cell measurement of Morton and Purcell, in which 15 per cent of the signal from overhead at 25° angle of solar depression passed through an absorption cell. This follows from the use of the theory of radiative transfer in a geocorona of optical thickness 2.3 and proper attention to the solar dip angle prevailing when the various experiments were performed. The result is that the model of a hydrogen geocorona containing 3 × 1012 atoms/cm2 in the daytime and 15 × 1012 atoms/cm2 at night can account for all Lyman α experiments, including the high-altitude and absorption cell experiments, if an external source of 0.7 × 10−3 erg/cm2 sec ster exists in the antisolar direction.