Spaced lidar and nightglow observations of an atmospheric sodium enhancement

On the night of August 25–26, 1979, a large enhancement was observed in the density of atmospheric sodium at a height of 95 km. The enhancement, lasting about 15 min and extending over a height range of about 2 km, was observed at three positions about 50 km apart. Increases in sodium airglow occurring almost simultaneously were observed at two points separated by 107 km. From the time lags between the occurrence of the enhancement at the various measuring points it is concluded that it was caused by the horizontal motion of a cloud of sodium with a density about 10 times the normal density at the peak of the sodium layer. The cloud appears to have been moving in an approximately SW direction with a velocity of the order of 200 m s −1 . On the assumption that the sodium was of meteoric origin, it is concluded that a minimum of 10 kg of meteoric material was necessary for its formation. From the magnitude of the observed increases in sodium abundance and sodium airglow a value of 3 × 10 13 m −3 is derived for the ozone density at 95 km.