SOLAR LYMAN SERIES LINE-PROFILES AND ATOMIC-HYDROGEN EXCITATION RATES

The atomic hydrogen Lyman series lines on the Sun were observed in high spectral resolution (0.14 Angstrom) during a Naval Research Laboratory sounding rocket flight in 1962 August, a period of low solar activity. The spectral fluxes which had not been previously published reveal strong intrinsic reversal of the Ly alpha and Ly beta lines, but Gaussian shaped lines are seen for Lyman 3-10. Placing the line fluxes on an absolute scale through use of independent measurements allows the calculation of excitation rates which are applicable to planetary and interplanetary hydrogen atoms. In these calculations, the effect of cascade was evaluated with a detailed model of the branching rates following Lyman series excitation. Application of the calculated excitation rates to measurements of Ba alpha emission in the terrestrial nightglow shows that emission lines arising from the 3 S-2 and 3 D-2 states can contribute 6.4% and 0.7% of the total emission, respectively, with the remainder resulting from fluorescence from direct Ly beta excitation of the 3 P-2 state. These results are consistent with ground-based observations which show line reddening with an excess intensity of 10% +/- 5% relative to that expected from Ly beta excitation of the 3 P-2 State of hydrogen.