Wave-associated sporadic neutral layers in the upper atmosphere

Clemesha, B. R.; Batista, P. P.; Simonich, D. M.

doi:10.1590/s0102-261x1997000300003

Cited by 7 publications

(6 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Based on the observations made earlier, Na s layers exhibited the following characteristics: they lasted from a few minutes to several hours; their peak heights generally followed a Gaussian distribution with the mean at $93 km; they mostly moved downwards; their occurrence time was highly variable with the location of observations (Kwon et al, 1988;Hansen and von Zahn, 1990;Clemesha et al, 1997;Qian et al, 1998;Gong et al, 2002;Prasanth et al, 2007). It should be mentioned that all these characteristics were from the lidar observations with conventional time resolutions (from 100 s to 9 min).…”

Section: Introductionmentioning

confidence: 95%

Behavior of sporadic Na layers on small time scale

Liu

2009

Journal of Atmospheric and Solar-Terrestrial Physics

View full text Add to dashboard Cite

Section: Introductionmentioning

confidence: 95%

Behavior of sporadic Na layers on small time scale

Liu

2009

Journal of Atmospheric and Solar-Terrestrial Physics

View full text Add to dashboard Cite

“…Results of the sodium layer measurements have been published in numerous papers over the past 30 years. These include studies of the sodium morphology [ Simonich et al , 1979], atmospheric tides [ Batista et al , 1985], the temperature profile [ Clemesha et al , 1999b] sporadic layers [ Clemesha et al , 1998] and global change [ Clemesha et al , 2003]. The recent publication by Kane et al [2001], showing an intriguing new type of sporadic sodium layer, prompted us to reexamine our recent data to see whether such structures occur at our location.…”

Section: Observations and Discussionmentioning

confidence: 99%

Sporadic structures in the atmospheric sodium layer

et al. 2004

View full text Add to dashboard Cite

[1] 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. These layers are much thinner than the background layer, last between a few minutes and many hours, and appear to be related to ionospheric sporadic E. A much more rare type of transient 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 enhanced sodium concentration.

show abstract

“…These were first observed in sodium by Clemesha et al (1978), and have subsequently been detected in other metals such as iron, calcium, potassium and magnesium. The definition of what constitutes an Ns layer is necessarily somewhat subjective, but it generally involves a layer of metal atoms between a few hundred meters and a few kilometers thick, with a concentration equal to or greater than twice that of the background metal layer which in the case of sodium has a typical width of around 10 km (Clemesha et al, 1997). A number of different mechanisms have been suggested for the formation of these layers, including direct meteor deposition (Clemesha et al, 1978(Clemesha et al, , 1988, the liberation of sodium from aerosol particles by auroral particle bombardment (von Zahn et al, 1987), redistribution of the background layer (Kirkwood and Collis, 1989), and sodium chemistry (von Zahn and Murad, 1990;Zhou et al, 1993;Zhou and Mathews, 1995), but none of these can account satisfactorily for all of the observed phenomena (Clemesha, 1995;Clemesha et al, 1999;Cox and Plane, 1998).…”

Section: Introductionmentioning

confidence: 99%

“…However, recent observations of Na s on a small timescale reveal that the instantaneous rate of change of Na atoms in a sporadic layer is often on the order of 100 cm −3 s −1 (Liu and Yi, 2009), which is too fast to be explained by the ion-molecule mechanism (Cox et al, 1993;Cox and Plane, 1998;Hansen and von Zahn, 1990). But as pointed out by Clemesha (1995) and Clemesha et al (1997), the observed rapid growth rates could well represent not the formation of neutral metal atoms, but the advection of a cloud of neutrals of limited horizontal extent over the observing site. However, the altitude and abundance variations of Es layers and Na s layers have been found to be highly correlated (Beatty et al, 1989); the vertical and temporal structures of the Na and electron densities are remarkably similar and the Na and electron density variations in phase .…”

Section: Introductionmentioning

confidence: 99%

Comparison of sporadic sodium layer characteristics observed at different time resolutions

et al. 2013

Self Cite

View full text Add to dashboard Cite

Abstract. Sporadic sodium (Na s ) layers, occurring in roughly the same height range as ionospheric sporadic-E layers, were first detected by lidar some 30 yr ago. Na s layers have a typical thickness of a few hundred meters to a few km, with peak atom concentrations several times that of the background layer. Despite a great deal of excellent work over the past decades, the source of Na s layers is still not altogether clear, partly as a result of our incomplete knowledge of Na s layer characteristics. In this paper we concentrate on some typical case studies chosen from the ∼ 127 h of sporadic sodium layer observations made at a time resolution of 1.5 s at Yanqing (115.97 • E, 40.47 • N), Beijing, China. This is a much better time resolution than what has been employed in most earlier measurements. The results show that the Na s layer peak heights are dispersed at slightly different although adjacent heights. When averaged over several minutes, as has been the case with most earlier measurements, the height scatter results in an apparent layer thickness of a few km. We conclude, therefore, that these dispersed peaks at different but adjacent heights constitute the 5 min Na s layer. Similar to the observations of sporadic-E-ion (Es) layers and meteor rate, we observe quasi-periodic fluctuations on a timescale on the order of several minutes in the peak height and the peak density of sporadic layers, which is a universal feature but concealed by the lower temporal resolution previously adopted. Spatially localized multiple scatterers and multiple thin layers with similar apparent movement in Na s layers are also found. We discuss the possible formation mechanism by the direct deposition of large swarms of micrometeoroids and demonstrate a typical example of meteor trails evolving into a Na s layer, which suggests that this mechanism might indeed occur.

show abstract

Wave-associated sporadic neutral layers in the upper atmosphere

Cited by 7 publications

References 0 publications

Behavior of sporadic Na layers on small time scale

Behavior of sporadic Na layers on small time scale

Sporadic structures in the atmospheric sodium layer

Comparison of sporadic sodium layer characteristics observed at different time resolutions

Contact Info

Product

Resources

About