High-altitude sporadic metal atom layers observed with Na and Fe lidars at 30°N

The seasonal/annual characteristics of the high-altitude sporadic metal atom layers are presented on the basis of extensive Na and Fe lidar measurements at 30°N during the past several years. It is found that the extremely high sporadic Na (Nas) and Fe (Fes) layers above 105 km occurred mostly during summer. They had long durations (a few hours) and broad layer widths (much larger than 2 km). Their absolute peak densities could be comparable to or even larger than those of the corresponding main layers on a few nights. By using all the raw data profiles including sporadic layers, we have constructed the contour plots of Na and Fe densities versus month and altitude at 30°N. The Na and Fe layers both exhibit evidence for summer topside extension, which is consistent with the earlier observations for K and Ca at different latitudes. The summer topside extension of mean metal atom layers might represent a universal phenomenon that is alike for different atom species, different geographic locations and different measurement years. The extremely high sporadic metal atom layers above 105 km occurring during summer give rise to the phenomenon.