Seasonal variations of the nocturnal mesospheric Na and Fe layers at 30°N

Abstract

[1] The complete seasonal variation patterns of the nocturnal mesospheric Na and Fe layers over Wuhan, China (30°N), have been established on the basis of several years of Na and Fe lidar measurements. Both the Na and Fe layer column abundances show strong annual variations as well as moderate semiannual variations with maxima in winter and double minima from late spring to midautumn (note that only one night of Fe data is presently available between mid-May and mid-July). The seasonal variation in the Fe abundance is evidently stronger than that of Na. The Na layer abundance has an annual mean of $2.5 Â 10 9 cm À2 , while this value for Fe is $7.5 Â 10 9 cm À2 . The Na and Fe centroid heights are dominated by semiannual oscillations with similar phases. The mean centroid heights are $91.4 km for Na and $88.7 km for Fe. The Na RMS width exhibits a strong semiannual oscillation with the layer slightly broader in winter, whereas the Fe width varies principally annually with a maximum in winter. The mean RMS widths of the Na and Fe layers are 4.5 and 4.1 km, respectively. The seasonal characteristics of the Na and Fe layers observed at 30°N have been compared with those currently available at other latitudes. The seasonal ratios of their abundances are smaller compared with 40°N and the South Pole. Their centroid heights and RMS widths also show less seasonal variations than the counterparts at all other latitudes. The annual mean Na and Fe abundances are about 60-77% of the counterparts at 40°N, 18°N, and the South Pole. This suggests that both the nocturnal Na and Fe layers have a low-abundance region around 30°N. On the basis of the results observed at the three latitudes in the Northern Hemisphere, the annual mean Fe layer width decreases with increasing latitude.

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

“…2, the Na column abundance, centroid height and RMS width are respectively 2.8 × 10 9 cm −2 , 91.5 km, and 4.1 km, while the corresponding values for Fe are respectively 7.4×10 9 cm −2 , 88.8 km, and 3.6 km (see Table 1). The values of the column abundance and centroid height approach those derived in terms of the conventional arithmetic mean from the more extensive Na and Fe lidar measurements (including separate Na and Fe data) at Wuhan , while the values of the RMS width are slightly smaller than those given by Yi et al (2009). This is caused by the detection threshold criteria imposed on the layer boundaries.…”

“…This is consistent with the fact that Fe is the main component of the meteoric source, whereas the alkali metals are the minor ones (Heide and Wlotzka, 1995). Among the alkali metals, only the Na layer has a typical abundance value approaching that of the Fe layer (Kane and Gardner, 1993;Gardner et al, 2005;Yi et al, 2009). Hence a detailed quantitative comparison between the Na and Fe layers at a given site is feasible.…”

“…Meteoric ablation is believed to provide the substance source for the metal layers. Based on independent extensive lidar measurements, the average properties and seasonal variations of these layers have been respectively obtained at many locations (Megie and Blamont, 1977;Clemesha et al, 1979;States and Gardner, 1999;Plane et al, 1999b;Eska et al, 1999;Gerding et al, 2000;She et al, 2000;Gardner et al, 2005Gardner et al, , 2011Yi et al, 2009). Several one-dimensional gas-phase chemical models corresponding to different metal species such as Na, Fe, K, and Ca have been respectively developed to explain these observational results (Helmer et al, 1998;Plane et al, 1999b;Eska et al, 1999;Gerding et al, 2000;Plane, 2004;Gardner et al, 2005).…”

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

“…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.…”

A statistical study of sporadic sodium layer observed by Sodium lidar at Hefei (31.8° N, 117.3° E)

“…Many researchers consider that in the interpretation of the short-time scales atmospheric dynamics (such as gravity waves and tides), the sodium layer can be regarded as a passive tracer (Gardner and Shelton, 1985;Gardner and Voelz, 1987;Kwon et al, 1987;Bills and Gardner, 1993), due to the longer lifetime of sodium atoms above 85 km (Xu and Smith, 2003). Extensive lidar studies of the seasonal variations of the sodium layer were conducted at different latitudes in the 1970s (Gibson and Sandford, 1971;Megie and Blamont, 1977;Simonich et al, 1979;States and Gardner, 1999;Plane et al, 1999;She et al, 2000;Gardner et al, 2005;Yi et al, 2009). With the development of narrowband lidars (Bills et al, 1991;She et al, 1992;Bills and Gardner, 1993;Papen et al, 1995), the mesospheric temperature and wind measurements has complemented sodium observations and helped to us understand the dynamical process in the MLT region.…”