Distribution in the Upper Atmosphere of Sodium Atoms Excited by Sunlight

Abstract

Calculation is made of the distribution of atoms excited to the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state by solar radiation, direct and reflected from the earth for a model sodium layer between 70 and 100 km. Account is taken of the attenuation by resonance absorption of sunlight in the layer before the solar photons reach a given point in the layer. This absorption grossly modifies the scattered intensity at twilight, causing minima to appear at about 5° solar depression and reducing greatly the difference in scattering for thicknesses between 2×${10}^9$ ${\mathrm{cm}}^{-2\mathrm{}}$ and 2×${10}^{11}$ atoms/${\mathrm{cm}}^2$ in late twilight. The effect of imprisonment, not included, is expected to modify only the late twilight results.