Distribution in the Upper Atmosphere of Sodium Atoms Excited by Sunlight

Calculation is made of the distribution of atoms excited to the ²P3/2 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×{}10⁹ cm^-2 and 2×{}10¹¹ atoms/cm² in late twilight. The effect of imprisonment, not included, is expected to modify only the late twilight results.