Evidence of an extraterrestrial source for the mesospheric sodium layer

Lidar observations of the mesospheric sodium layer, made at São José dos Campos (23§S, 46§W), show three distinct types of organized structure in the vertical distribution of sodium. Profiles averaged over several days show a smooth but asymmetrical distribution. A sequence of profiles for a given night normally shows a wavelike structure which descends through the layer with time. Very occasion an extremely narrow peak is observed at a constant several hours. On one occasion a layer e, with scale heights of 700 m on the bottomside and 900 m on the topside, was observed to persist at a constant height for hours. It is concluded that such a layer could neither be produced by neutral density perturbations nor by photochemical processes and therefore indicates a source of sodium in the mesosphere.