LITHIUM, SODIUM, AND POTASSIUM IN THE TWILIGHT AIRGLOW

Abstract

A birefringent filter photometer has been used to measure the weaker twilight emissions due to free lithium and potassium atoms, the twilight sodium emission having been monitored simultaneously with an interference wedge photometer. Comparisons of the relative abundances Na/Li and Na/K with those found in meteorites and in sea water suggest that the principal sources are meteorites for the lithium, and the sea for the sodium and potassium.A spectacular seasonal variation of the twilight lithium has been found, showing a correlation with the occurrence of the Leonid meteor shower and with two unusual interplanetary dust showers, one during the interval November 15–18, and the other on February 2. Effects of high-altitude thermonuclear explosions are discussed and it is concluded that these can increase the brightness of twilight lithium emission by 1 to 2 powers of 10.The vertical distributions of all three elements have roughly the same shape. However, the maximum concentration of lithium occurs at 80 km, approximately 11 km below the sodium peak, while the maximum concentration of potassium occurs at about the same height as the sodium peak.The chemistry and ionization of alkalis in the upper atmosphere are considered. It is suggested that the degree of ionization is negligible, and a fast recombination process is discussed. A mechanism for vertical transport of sodium from the lower atmosphere is suggested.