Winter enhancement of atomic lithium and sodium in the polar upper atmosphere

Winter twilight spectrophotometric observations of alkali metal resonance line emissions over Svalbard yield column densities of 1.9 × 10 7 Li atoms cm −2 and 1.1 × 10 10 Na atoms cm −2 near the polar mesopause for November 1978 through January 1979. The latter density is high but consistent with observations elsewhere. The former is at least twice as large as either the sporadic increases or the seasonal peak observed at lower latitudes and was not significantly diminished according to similar observations in December 1977 and November 1979. Other polar observations nearer the equinox indicate lower Na abundances, implying the existence of a December–January polar seasonal maximum.