Some ubiquitous features of the mesospheric Fe and Na layer borders from simultaneous and common‐volume Fe and Na lidar observations

Abstract

[1] High-accuracy atom density profiles, obtained by the simultaneous and commonvolume Fe and Na lidar measurements at Wuhan, China (30.5°N, 114.4°E), reveal some ubiquitous features of the Fe and Na layers on their borders. The Fe and Na lower boundaries show consistently a delicate stratification in which the lower boundary of the Fe layer is in general slightly higher than or coincident with that of the Na layer, with an overall mean altitude difference being about 0.2 km. Despite the existence of considerable vertical displacements, the two lower boundaries vary always following almost the same track. The overall correlation coefficient between them is as high as 0.96. This ubiquitous delicate stratification of the measured lower boundaries (nearly coincident density cutoff ) suggests strongly that the undersides of Fe and Na layers are controlled by the same or very similar processes. The upper boundary of the Na layer is always several kilometers higher than that of the Fe layer. A relatively weak positive correlation is also persistently observed between the two upper boundaries. Weak sporadic layering events frequently occur on the upper extent of the metal layers. They may impair the correct determination of the upper boundaries of the normal metal layers and consequently weaken the correlation. Both the Fe and Na layers often show an evidently steeper density gradient on the underside than on the upper extent, and the borders of the Fe layer are clearly steeper than those of the Na layer. The explanation to these ubiquitous features needs further experimental and modeling efforts.

Average properties and small-scale variations of the mesospheric Na and Fe layers as observed simultaneously by two closely colocated lidars at 30° N

“…They noticed that even though the individual density profiles appeared quite different, the temporal variations of Na and Fe layer parameters (abundances, centroid heights, and RMS widths) were highly correlated in most cases. The simultaneous and common-volume Na and Fe lidar observations at 30 • N revealed that Na and Fe lower boundaries always follow almost the same track and show consistently a delicate stratification with the Fe lower boundary being in general slightly higher than or coincident with that of the Na layer (Yi et al, 2007(Yi et al, , 2008. In addition, the Na layer always shows a few kilometers more extension on its top side than the Fe layer.…”

“…The mean profiles will quantitatively show the relationship of the two background metal layers. In contrast to our previous work that only focuses on the relationship between the Na and Fe layer boundaries (defined by a given small density criterion) (Yi et al, 2008), here we will examine the relation between the Na and Fe density variations at all fixed altitudes over the main metal layer. An intriguing ubiquitous connection between the Na and Fe density variations at fixed altitudes on the layer bottom side is revealed for the first time.…”

Simultaneous, common‐volume lidar observations and theoretical studies of correlations among Fe/Na layers and temperatures in the mesosphere and lower thermosphere at Boulder Table Mountain (40°N, 105°W), Colorado

“…An example is shown in Figure 7a for 4 September 2012. Note that in the current study, the lower and upper boundaries of a metal layer are defined to be the altitudes where the densities are 2% of the nightly mean peak density, instead of a fixed density for two lidars as presented in Yi et al [2008]. For the total 704 pairs of Fe and Na density profiles over 12 nights, the Fe layer lower boundaries are plotted versus the Na lower boundaries in Figure 7b.…”

“…[27] A detailed study by Yi et al [2008] from 26 nights of observations at Wuhan (30.5°N, 114.4°E), China, has found a close correlation between Fe and Na boundary altitude variations, especially at the layer bottomside. Our Table Mountain observations reveal similar behavior, with higher correlations at the lower boundary (nearly 99%) and slightly lower correlation (~70%) at the upper boundary.…”

“…Unfortunately, observations of multiple species are rare, although general properties of Fe and Na layers have been reported by several groups independently [Tilgner and von Zahn, 1988;Plane et al, 1999;States and Gardner, 1999;Raizada and Tepley, 2003;Gardner et al, 2011] and by a few correlative observations Gardner et al, 1993Gardner et al, , 2005. The lidar group at Wuhan has undertaken extensive simultaneous Fe and Na observations with broadband resonance lidars [Yi et al, 2008[Yi et al, , 2009. Several unique features have been characterized from a large amount of data [Chen and Yi, 2011;Ma and Yi, 2010], but definitive explanations for these features are still lacking.…”