The annual variation of the height of the atmospheric sodium layer at 23°S: possible evidence for convective transport

On the basis of a long series of lidar measurements made at São José dos Campos, it is found that the centroid height of the atmospheric sodium layer is about 1 km lower in November than during the rest of the year. Photometric measurements of the OH(9,4) and OI 557.7 nm airglow intensities, observed at a nearby location, show that these emissions have maximum values at this time of the year. The hydroxyl emission shows a sharp increase in intensity by about 20% in November, and the atomic oxygen emission has a broader peak in October, November, and December. There is a strong inverse correlation between the seasonal variations in sodium layer centroid height and the OH intensity, with a correlation coefficient of 0.86 and a regression coefficient of −89±16 Rayleighs km −1 . It is suggested that the anticorrelated variations in sodium layer height and airglow intensity could be the result of seasonal changes in convective transport in the lower thermosphere.