Sporadic structures in the atmospheric sodium layer

Abstract

The sporadic occurrence of layers of enhanced concentration of meteoric metals in the vicinity of the mesopause has been observed by lidar at many locations. Thes layers layer has been reported in the literature only once, by Kane et al. [2001]. The layers in question, observed in sodium by a lidar operating at Arecibo (18.3°N,66.7°W), appear as C-shaped structures in the lidar height/time display. The structures, which have been observed at around 100 km, with durations around 30 min, appear not to be related to normal sporadic metals layers, and the Arecibo workers suggest that they might be produced by wave-breaking or Kelvin-Helmholtz billows. At São José dos Campos (23°S, 46°W) we observe C-structures in the sodium layer only very occasionally, but an analysis of their formation, together, with simultaneous meteor winds measurements, suggests that the observed structures might be the result of wind-shear distortion of preexisting clouds of enchanced sodium concentration. Copyright 2004 by the American Geophysical Union.