Terrestrial Absorption in the Sodium D2 Line

An experimental investigation of the abundance of upper atmospheric sodium at Boca Raton, Florida, using high resolution absorption spectroscopy, is described. The discussion is based primarily on data taken from January to October, 1968, but W. Lammer's data of September through November, 1967, is used for the seasonal analysis. A description of the data and the method of analysing it are presented, with emphasis on the theory underlying a computer method of analysis.
Measurements indicate a seasonal variation of about a factor of two, with a sharp drop off in late February, 1968. A maximum average monthly abundance of 5.4 ± 2.0 x 10^9 atoms/cm^2 in a vertical column in October, 1967, and a minimum average of 2.6 ± 0.6 x 10 atoms/cm^2 in March, 1968, was measured. The average for the twelve months beginning November, 1967, was 3.6 x 10^9 atoms/cm^2 . In general, uncertainties of the order of 50% are present in the measured abundance determined by a single recorder trace. This value is generally smaller for those traces which are less noisy, and which show a larger amount of terrestrial sodium absorption. No correlation between the abundance and hurricanes has been established. If any correlation exists, it probably is smaller than the uncertainty of our measurements.