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Dependence of mesospheric Na and Fe distributions on electron density at Arecibo
© Raizada et al. 2015
- Received: 2 March 2015
- Accepted: 2 September 2015
- Published: 11 September 2015
The Erratum to this article has been published in Earth, Planets and Space 2015 67:202
We present case studies of the mesospheric alkali and non-alkali metals, Na and Fe, along with electron concentrations [Ne] obtained from measurements made at Arecibo on nights of 17–18 and 18–19 March 2004. The background mesospheric conditions as recorded by an airglow all-sky imager displayed ripple- and band-type structures on these nights. Both of the metals display detailed structures within their neutral sporadic layer but are more pronounced in Na than for Fe. A sporadic-E (Es) with electron concentrations [Ne] exceeding 3000 electrons cm−3 is accompanied by a strong Na enhancement and a weak sporadic Fe (Fes) layer around 95-km altitude. The concentration of Fe+ and Na+ is estimated to be close to 600 and 30 ions.cm−3, respectively, within the sporadic-E layer. In order to investigate ion-neutral coupling, a correlative analysis was performed in two altitude regions. Similar features are seen between neutrals and electrons in the 96–100-km altitude range, while within the altitude range of 80–90 km, an opposite behavior is seen. A comparative study between neutral layers below 90 km often referred to as the main or permanent layer and sporadic activity above 90 km reveals different characteristics for alkali and non-alkali metal. Fe concentrations in the main layer are higher than in Fes resulting in a density ratio of less than 1 determined from two layers of 3 km thickness centered at 97 and 87 km. For the case of Na, the ratio exceeds 1 during Es activity on both the nights.
The case studies discussed in this work facilitate our understanding of different factors that can influence the sporadic activity in alkali and non-alkali metals. In a region dominated by ion-molecule chemistry, temperature fluctuations that can be induced by wave activity will have more impact on Na than for Fe within their layers depending on altitude.
- Mesospheric layers
- Ion-neutral coupling
A variety of interesting phenomena occur in the mesospheric region of the Earth’s atmosphere that includes sporadic-E (Whitehead, 1989), polar mesospheric summer echoes (Rapp and Lübken, 2004), and deposition of meteoric metals (Gadsden, 1969; Plane, 2003). The existence of metals in the Earth’s mesosphere was first established using airglow studies (Brown, 1973). With the advent of laser technology, several groups reported temporal and altitudinal distributions of various metals like Na, K, Ca, and Fe using ground-based lidar systems located at different latitudes (Alpers et al., 1990,1994; Tepley et al., 2003; Collins et al., 1994; Clemesha et al., 2004; Sridharan et al., 2009; Gardner et al., 2011; Raizada et al., 2011; Yuan et al., 2012). This led to the development of modeling efforts to understand mesospheric chemistry and the role of meteor input in the distribution of metals (Plane, 2003). One of the most abundant metals in meteoroids as well as in the mesosphere is atomic Fe. Upper atmospheric atomic Fe has been studied from different locations (Granier et al. 1989, Alpers et al., 1990; Kane and Gardner, 1993; Chu et al., 2006; Raizada and Tepley, 2002, Huang et al., 2013). Raizada and Tepley (2003) found significant latitudinal differences in the Fe distribution. Observations of Fe at South Pole and Rothera have shown seasonal differences in its distribution (Gardner et al., 2011). In addition to the main or permanent metal layer, earlier studies have shown the occurrence of thin regions of enhanced concentrations occasionally, generally referred to as sporadic layers in the neutrals. A strong link between these sporadic layers and sporadic-E has been suggested in many earlier studies (Kirkwood and von Zahn, 1991; Gardner et al., 1993; Alpers et al., 1994; Collins et al., 2002; Williams et al., 2007; Zhou et al., 2008). Sporadic-E is often patchy in nature, i.e., the electron concentrations display spatial variations and hence result in inhomogeneity in the atmosphere (Miller and Smith, 1975). Observations of Fe by Alpers et al. (1990) from Andoya, Norway (69° N) revealed frequent occurrences of Fes within 15 h. A more comprehensive comparison of Na and Fe layers at mid-latitudes showed sporadic activity to be very prominent for Fe but not so for Na (Kane and Gardner, 1993). The latitudinal variation in the occurrence of Nas layers is evident from the following studies: Nagasawa and Abo (1995) reported frequent observations of sporadic Na layers above Tokyo (35.6° N). Yi et al. (2002) studied the seasonal variability of Nas layers over Wuhan (30.5° N), China and found that their occurrence rate maximized in summer. Their study revealed broader Nas widths as compared to low and high latitudes. Recent work by Wang et al. (2012) have shown that at 40° N double layers in Na occurred between 105 and 130 km with about 17 such events per 319 of total observations. Later on, Dou et al. (2013) analyzed Na lidar data from four sites (40° N, 31° N, 30° N, 19° N) representing mid- and low latitudes in China and found that the occurrence rate of Na sporadic layers were similar at locations less than 31° N but about 3 time smaller at 40° N. Nas layers are common at low and high latitudes (Batista et al., 1989; Kwon et al., 1988; Hansen and von Zahn, 1990).
The occurrence of both sporadic-E and neutral layers has been linked to several processes that include neutralization, the presence of wind shears, and advection (Gardner et al., 1993; Tepley et al., 2003; Plane, 2004; Raizada et al., 2011,2012). Recently, Yuan et al. (2014) related the seasonal variations of Nas and Es layers to the convergence of metal ions in summer, while ion diffusion appeared to dominate in wintertime. Zhou et al. (2008) investigated the seasonal and local time variations of Fes and their relation to sporadic-E at Arecibo (18° N). They reported three nights of simultaneous observations of Fe and electron concentrations, where good correlations were seen in the occurrence of Fes with Es layers. A correlative analysis between Na and Fe layers observed in China (30° N) revealed that the lower sides of these metal layers track each other extremely well, while the densities at the top side do not follow each other (Yi et al., 2008). They found that Na layer is broader and extends to higher altitudes; its upper boundary is about 5.2 km higher, while the lower boundary is ~0.6 km lower than Fe. Also, the temporal behavior of the upper boundary displayed some differences and was attributed to be likely due to sporadic layers. Recently, Yue et al. (2013) extended this study for the same metals observed at Arecibo with similar results showing that altitudinal dependence of Na and Fe correlations are global in nature. Both the studies did not compare the similarities or differences in sporadic activities, which is one of the goals in the current study.
Even though several studies of metal layers have been performed from different locations that have been mentioned in the above paragraphs, they were focused on other aspects of the metallic layers. In this study, we examine two cases of Na and Fe distributions along with simultaneous electron concentrations that were obtained using co-located resonance fluorescence lidars (RFLs) and incoherent scatter radar (ISR) at Arecibo (18.35° N, 66.75° W). The examples used in this investigation offer an excellent opportunity to improve our understanding related to metal layer response to sporadic-E and hence provide better insight about ion-neutral coupling. This study aims to understand the role played by various atmospheric constituents and other factors that may be responsible for differences observed in metallic layer.
The RFL system used for the measurements reported in this work consists of a single state of the art, Nd:YAG laser that pumps two identical dye lasers. The pumping was performed by splitting the second harmonic at 532 nm with 14 W of average power in each beam at 50-Hz repetition rate. The two dye lasers were tuned to generate resonance wavelengths of Na and Fe at 589 and 372 nm, respectively. We used the rhodamine 610 dye to generate the fundamental, 589-nm emission for Na, while the generation of the UV emission for 372 nm required a sum-frequency technique. So, for the second dye laser, we combined rhodamine 590 and 610 dyes for a dye fundamental at 572 nm and then sum frequency mixed with the IR residual from the Nd:YAG at 1064 nm to generate photons at 372 nm. The average power at this wavelength was ~1 W while at 589 nm, it was ~4 W. The backscattered photons were collected using an f/15 Cassegrain type telescope with a 0.8 m diameter. An optical fiber with a core diameter of 1.5 mm directed the light to a dichroic filter that splits the incoming beam to the detectors and narrow band interference filters of ~1-nm bandwidth at FWHM. EMI 9863-350B and Hamamatsu R943-02 photomultiplier tubes were used to collect the light at 372 and 589 nm, respectively. Other instrumental details can be found in the earlier work (Raizada and Tepley, 2002; 2003; Raizada et al., 2004; Tepley et al., 2003; Raizada et al., 2011; 2012).
The range resolution for all the lidar data presented here is 300 m. The temporal resolution for the Na and Fe datasets was ~1 min, and it was ~2 min for Ne.
The electron concentrations were derived from standard Barker-coded power profile measurements that were made during one of the topside ISR runs at Arecibo (González and Sulzer 1996). The technique utilizes a 13-baud, 4 μs/baud coded pulse, yet we oversampled the data by a factor of 2 to yield a bin size of 300 m (Ioannidis and Farley 1972).
The background atmospheric conditions over Arecibo were monitored by using The Penn State Allsky Imager (PSASI), which records nighttime airglow at three different optical wavelengths (557.7, 630.0, 777.4 nm) that are emitted from different layers of the ionosphere. The 557.7-nm airglow comes from the upper mesosphere (~96 km) or E-region and its intensity is proportional to column-integrated [O]3 (cube of concentration of atomic oxygen) in the emission layer. Since atomic oxygen is one of the major sources of ions and electrons in the lower E-region of the ionosphere, this emission can be used to monitor both neutral phenomena (such as gravity waves) and electrodynamics near this altitude. More details on PSASI, airglow, and ionospheric phenomena revealed by it can be found in Seker et al. (2007).
To obtain accurate information from the all-sky images, each image was processed in the following way. First, the images are spatially calibrated using star locations to find the geographic directions. Then, the stars are removed using a median filter and contrast is enhanced to better show the phenomena of interest (gravity waves). Finally, based on the location and coverage of the imager and height of the emission layer, the images are un-warped (to correct for the fish-eye lens effect) and then mapped to geographical coordinates.
Co-located ISR and RFL measurements corresponding to the different metals offer an excellent way to understand mesospheric processes. Data pertaining to an alkali and a non-alkali meteoric metal measured at Arecibo on two consecutive nights, 17–18 and 18–19 March 2004, are discussed. These two cases represent sporadic-E events that are accompanied by a strong enhancement in the neutral Na but relatively weaker in Fe. We discuss these two nights in the following sections.
17–18 March 2004
18–19 March 2004
This work investigates two cases based on consecutive nights of lidar and ISR data obtained from Arecibo. Earlier studies have associated Es layers with neutral distribution mainly through ion-molecule chemistry (Gardner et al., 1993; Collins et al., 2002; Raizada and Tepley, 2002; Zhou et al., 2008). The unique set of observations presented here illustrates the differences in neutral distribution and offers an excellent opportunity to understand the processes that can be responsible for such different behaviors observed for alkali and non-alkali metals. In this regard, it is important to compare the average/peak column abundances of Na and Fe in the main layer and also within Es.
Average and peak abundances for Na, Fe, and Ne on two nights at Arecibo
Na abundance (109 × cm−2)
Fe abundance (109 × cm−2)
Ne abundance (109 × cm−2)
17 March 2004
18 March 2004
Comparing the relative abundances of ions of chondrites in the MLT region
6.3 × 10−2
7.4 × 10−2
9.1 × 10−2
6.8 × 10−2
2.8 × 10−2
3.9 × 10−2
Earlier studies from Arecibo have shown a good correlation between sporadic-E and Fes layers (Raizada and Tepley, 2002; Zhou et al., 2008). The current study shows a good correlation between neutral sporadic and Es layers in the altitude range of 96–100 km. The neutralizations of both Na+ and Fe+ have negative temperature dependence, which can explain such behavior. Between 85–90-km altitude intervals, the correlation between Na and Fe is similar when the sporadic-E descends to lower altitudes; otherwise these metals display different response to Ne. The simultaneous occurrence of sporadic neutral and Es layers also results in good correlation between Na and Fe but results in poor correlation in absence of such coincidence. Yue et al. (2013) investigated altitudinal correlations between Na and Fe and found negative correlation coefficients (r) occurring in a narrow middle region encompassed by positive r values at the top and bottom parts of the layers. They demonstrated that the layer structure for the case of Na and Fe is mainly determined by chemistry, while the correlation between the two species is governed by gravity wave-induced density fluctuations. However, they determined r using the average data for all the night and to obtain its temporal variation, a sliding window of 1 h was used. Additionally, the work presented by Yue et al. (2013) did not study the influence of electron concentration on the neutrals due to the lack of ISR data. Since in this study, we aim at investigating the ion-neutral coupling, the correlations have been determined for specific altitude regions based on chemical differences. Later, we determine the chemical lifetimes of Fe and Na ions to shed more light on correlations.
The lidar gives the temporal variation of a particular metal along the line of sight and its altitudinal variation is often referred to as “lidargrams” (Clemesha et al., 2004). Thus, both radar and lidar sample the line of sight volume of the atmosphere and do not provide any information regarding the spatial variability in horizontal dimensions. Collins et al. (2002) has discussed this aspect in detail. Earlier measurements have revealed structured sporadic-E with sizes ~300 m, limited by the range resolution of the radar (Miller and Smith, 1975). Later on, Hysell et al. (2012) found irregular sporadic-E with periodic structuring that was attributed to shear instability in the neutral flow. Though the medium can be inhomogeneous, the altitudinal/temporal resolution profiles at a given location can be useful to determine the variations, which can be caused either by dynamics or chemistry. A good correlation between metals is often observed apart from inhomogeneity in the atmosphere. The evidence comes from similarity between the lower boundary of Na and Fe layers as observed in the data presented in this study (Figs. 1 and 4), which is consistent with earlier observations (Yi et al., 2008; Yue et al. 2013). This suggests that local dynamics plays a significant role in the temporal variation of Na and Fe on any given night. The influence of Es through ion-neutral coupling is evident from high correlations between the metals and Ne in the presence of sporadic-E. In the absence of strong Es, particularly between 85- and 90-km regions, Na and Fe display anti-correlation but changes to good correlation as the sporadic-E layers descend to lower altitudes (Fig. 2). This elucidates a different sensitivity of Na and Fe to electron concentrations. Also, the concentration ratios evaluated for both the neutral in the upper altitudes and within the main layer reveal that the latter is stronger in the case of Fe relative to its sporadic, which is an opposite behavior to the alkali metal, Na, on the two nights reported here. The possible reasons for this different sporadic activity in the neutral Fe and Na are discussed below.
Earlier studies have shown that the structure and distribution of different mesospheric metals are governed both by dynamics and chemistry (Plane, 2003; Gerding et al., 2000; Yue et al. 2013). To investigate the dynamical activity on these nights, we use the PSASI imager that reveals wave characteristics on these two nights. It is to be noted that imagers are well-suited instruments that provide information about gravity waves, MSTIDS (Makela et al., 2010). Figure 9a displays a GW event on the night of 17–18 March 2004 as measured from the O(1S) 557.7-nm emission. This night is characterized by ripple-type (smaller wavelength, faster speed) and band-type (larger wavelength, slower speed) gravity waves (GWs) that were seen from 02:00 until 05:00 AST. Two separate GWs were observed around 03:00 AST. The first GW packet appeared southwest of the Arecibo and was aligned along the northwest-southeast direction and moved slightly westward of the north direction, disappearing toward the northwest of Arecibo. The horizontal wavelength, speed, and period of the GWs were measured as ~25 km, 2.5 km/min (150 km/h or ~40 m/s), and 10 min, respectively. These values are typical for E-region band-type (large-scale, slow speed) GWs. The second GW packet appeared southeast of Arecibo and propagated northward. The horizontal wavelength, speed, and period of the GWs were measured as ~10 km, 1.5 km/min (90 km/h or 25 m/s), and ~7 min, respectively. This wavelength value is typical for E-region ripple-type GWs (Chung et al., 2003).
Figure 9b shows the wave activity, again observed at 557.7 nm, obtained on the night of 18–19 March 2004. This night is also characterized by both band-type and ripple-type GWs. Ripple-type GWs were dominant, especially during 02:30–03:30 h AST and all-sky band-type GWs were dominant during 04:00 h AST. The ripple-type GWs appeared northeast of Arecibo, were aligned along northeast-southwest, and moved toward the northwest, disappearing north of the site. The horizontal wavelength, speed, and period of the GWs were measured as ~20 km, 2.5 km/min (150 km/h or ~40 m/s), and 8 min, respectively. The band-type GWs covered the whole sky, were aligned northwest-southeast, and propagated southwestward. The horizontal wavelength, speed, and period of the band-type GWs were measured as ~14 km, 1 km/min (60 km/h or ~17 m/s), and 14 min, respectively.
Thus, the PSASI imager data reveal that both nights had similar wave structure, which can also cause temperature perturbations. The occurrence of ripple-type structures seen on both the nights suggests that the atmospheric conditions are conducive for dynamical instabilities, which are likely to occur in the presence of strong horizontal shears. As discussed in the above paragraph, the ripple-type structures appear to propagate in meridional direction with a component in the zonal direction. This implies the possibility of existence of large horizontal wind shears that are required for Es formation (Whitehead, 1989). This is consistent with the ISR observations of sporadic-E layer on both the nights. Recent studies by Fytterer et al. (2014) revealed that the amplitude of 8-h Es maximizes during equinox at low and mid-latitudes in both hemispheres.
The differences in lifetime sensitivity to electron concentrations manifest in correlation seen in the Figs. 2 and 6. The anti-correlation between Na and Fe in the lower part (85–90 km) on both the nights can possibly be attributed to longer Fe+ lifetimes and higher sensitivity to Ne concentrations relative to Na.
This work suggests that the stronger Na sporadic layer can result from the faster neutralization process, which is more sensitive to temperature changes compared with Fe at altitudes above 100 km. Our data suggests that the stronger structures in the case of Na compared with Fe within sporadic neutral layer are more likely to be the manifestation of temperature-induced lifetime variability. Thus, it appears that Na acts as better tracer for studying gravity wave-induced fluctuations at higher altitudes.
Two adjacent nights of simultaneous Na, Fe, and Ne data from Arecibo were studied to examine their characteristics. Fe+, being one of the most abundant ions in the upper mesosphere, makes its neutral species counterpart an interesting element to be studied, in particular when electron concentrations and measurements of other metals are available. An estimation of the concentration of ions within sporadic-E events observed at Arecibo during nighttime reveals that the Fe+ and Na+ concentrations are ~600 and 30 ions.cm−3, respectively. The strength of the neutral sporadic layers is determined by evaluating the ratios of the concentrations above 90 km to that of the main layer. This value is larger for Na compared with Fe, indicating that sporadic activity in Na is stronger than the more abundant metal, Fe on the two nights reported here. Thus, this suggests that each metal responds differently to Es layers. Several factors like dynamics and chemistry can contribute to the differences in sporadic activity. Airglow images obtained at 557.7 nm indicate similar dynamical activity on the two nights with ripple-type structures suggesting the occurrence of dynamical instabilities. This indicates the presence of large shears in the horizontal winds that are required for Es formation. The sporadic-E activity observed in the ISR data supports this scenario. Inhomogeneity alone cannot account for a weaker sporadic Fe layer relative to its main layer, as this is one of the dominant species in the mesosphere. A comparison of lifetimes of these two metals reveals a faster neutralization for the alkali metal (Na), which is more sensitive to temperature changes than for changes in minor species concentrations. To summarize, the weaker, or less pronounced, sporadic events in Fe are most likely due to slower neutralization rates along with their lesser sensitivity to temperature changes.
Future work should focus on understanding the climatological distribution of simultaneous measurements of Na and Fe. Such studies will facilitate the appreciation of the role of dynamics and chemistry that can influence the structure of the metals layers and contribute to their seasonal as well as latitudinal and altitudinal variability.
We acknowledge the National Science Foundation (NSF) grants AGS-1243063, AGS-1241436 to SRI International, USA and AGS-1243133 to Miami University, USA that allowed us to carry out the research for this paper. J. D. Mathews’ and part of S. Sarkhel’s component were supported by a NSF grant AGS 1241407 to The Pennsylvania State University, USA. S. Raizada is extremely grateful to Raúl García for providing technical support. The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968) and in alliance with Ana G. Méndez—Universidad Metropolitana and the Universities Space Research Association.
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- Alpers M, Höffner J, von Zahn U (1990) Iron atom densities in the polar mesosphere from lidar observations. Geophys Res Lett 17:2345–2346View ArticleGoogle Scholar
- Alpers M, Höffner J, von Zahn U (1994) Sporadic Fe and E layers at polar, middle, and low latitudes. J Geophys Res 99:14,971–14,985View ArticleGoogle Scholar
- Batista PP, Cieraesha BR, Batism IS, Simonich C DM (1989) Characteristics of the sporadic sodium layers observed at 23° S. J Geophys Res 94:15,349–15,358View ArticleGoogle Scholar
- Behnke RA, Vickrey JF (1975) Radar evidence for Fe+ in a sporadic-E layer. Radio Sci l0:325–327View ArticleGoogle Scholar
- Brown TL (1973) The chemistry of metallic elements in the ionosphere and mesosphere. Chem Rev 73(6):645–667View ArticleGoogle Scholar
- Chu X, Espy PJ, Knott GJ, Diettrich JC, Gardner CS (2006) Polar mesospheric clouds observed by an iron Boltzmann lidar at Rothera (67.5° S, 68.0° W), Antarctica from 2002 to 2005: properties and implications. J Geophys Res 111:D20213. doi:10.1029/2006JD007086 View ArticleGoogle Scholar
- Chung J-K, Kim YH, Won Y-I (2003) Observation of mesospheric waves with an all-sky camera in Korean Peninsula. Adv Space Res 32(5):825–830. doi:10.1016/S0273-1177(03)00414-9 View ArticleGoogle Scholar
- Clemesha BR (2004) A review of recent MLT studies at low latitudes. Ann Geophys 22:3261–3275. doi:10.5194/angeo-22-3261-2004 View ArticleGoogle Scholar
- Clemesha BR, Batista PP, Simonich DM, Batista IS (2004) Sporadic structures in the atmospheric sodium layer. J Geophys Res 109:D11306. doi:10.1029/2003JD004496 View ArticleGoogle Scholar
- Collins RL, Nomura A, Gardner CS (1994) Gravity waves in the upper mesosphere over Antarctica: lidar observations at the South Pole and Syowa. J Geophys Res 99:5475–5485. doi:10.1029/93JD03276 View ArticleGoogle Scholar
- Collins SC, Plane JMC, Kelley MC, Wright TG, Soldan P, Kane TJ, Gerrard AJ, Grime BW, Rollason RJ, Friedman JS, Gonzalez SA, Zhou Q, Sulzer MP, Tepley CA (2002) A study of the role of ion–molecule chemistry in the formation of sporadic sodium layers. J Atmos Terr Phys 64:845–860Google Scholar
- Cox RM, Plane JMC (1997) An experimental and theoretical study of the clustering reactions between Na+ ions and N2, O2 and CO2. J Chem Soc Faraday Trans 93:2619–2629View ArticleGoogle Scholar
- Friedman JS, Tepley CA, Raizada S, Zhou QH, Hedin J, Delgado R (2003) Potassium Doppler-resonance lidar for the study of the mesosphere and lower thermosphere at the Arecibo Observatory. J Atmos Sol Terr Phys 65:1411–1424. doi:10.1016/j.jastp.2003.09.004 View ArticleGoogle Scholar
- Dou XK, Qiu SC, Xue XH, Chen TD, Ning BQ (2013) Sporadic and thermospheric enhanced sodium layers observed by a lidar chain over China. J Geophys Res Space Phys 118:6627–6643. doi:10.1002/jgra.50579 View ArticleGoogle Scholar
- Friedman JS, Chu X (2007) Nocturnal temperature structure in the mesopause region over the Arecibo Observatory (18.35° N, 66.75° W): seasonal variations. J Geophys Res 112:D14107. doi:10.1029/2006JD008220 View ArticleGoogle Scholar
- Fytterer T, Arras C, Hoffmann P, Jacobi C (2014) Global distribution of the migrating terdiurnal tide seen in sporadic E occurrence frequencies obtained from GPS radio occultations. Earth Planets Space. doi:10.1186/1880-5981-66-79.
- Gadsden M (1969) Antarctic twilight observations, 1, search for metallic emission lines. Ann Geophys 25:667–677Google Scholar
- Gardner CS, Kane TJ, Senft DC, Qian J, Papen GC (1993) Simultaneous observations of sporadic E, Na, Fe, and Ca+ layers at Urbana, Illinois: three case studies. J Geophys Res 98(D9):16,865–16,873Google Scholar
- Gardner CS, Chu X, Espy PJ, Plane JMC, Marsh DR, Janches D (2011) Seasonal variations of the mesospheric Fe layer at Rothera, Antarctica (67.5° S, 68.0° W). J Geophys Res 116:D02304. doi:10.1029/2010JD014655 Google Scholar
- Granier C, Jegou JP, Megie G (1989) Iron atoms and metallic species in the Earth’s upper atmosphere. Geophys Res Lett 16:243–246View ArticleGoogle Scholar
- Gerding M, Alpers M, von Zahn U, Rollason RJ, Plane JMC (2000) The atmospheric Ca and Ca+ layers: mid-latitude observations and modeling. J Geophys Res 105:27131–27146Google Scholar
- González SA, Sulzer MP (1996) Detection of He+ layering in the topside ionosphere over Arecibo during equinox solar minimum conditions. Geophys Res Lett 23:2,509–2,512View ArticleGoogle Scholar
- Hansen G, von Zahn U (1990) Sudden sodium layers in polar latitudes. J Atmos Terr Phys 52:585–608View ArticleGoogle Scholar
- Helmer M, Plane JMC, Qian J, Gardner CS (1998) A model of meteoric iron in the upper atmosphere. J Geophys Res 103:10913View ArticleGoogle Scholar
- Md Mosarraf Hossain, Vineeth C N, Nair S, Sumod G K, Pant T K (2014) Highly varying daytime sodium airglow emissions over an equatorial station: a case study based on the measurements using a grating monochromator. Earth Planets Space. doi:10.1186/1880-5981-66-56.
- Huang W, Chu X, Gardner CS, Wang Z, Fong W, Smith JA, Roberts BR (2013) 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. J Geophys Res 118:8748–8759. doi:10.1002/jgrd.50670 Google Scholar
- Hysell DL, Nossa E, Larsen MF, Munro J, Smith S, Sulzer MP, González SA (2012) Dynamic instability in the lower thermosphere inferred from irregular sporadic E layers. J Geophys Res 117:A08305. doi:10.1029/2012JA017910 Google Scholar
- Ioannidis G, Farley DT (1972) Incoherent scatter observations at Arecibo using compressed pulses. Geophys Res Letts 7(7):763–766Google Scholar
- Kane TJ, Gardner CS (1993) Structure and seasonal variability of the nighttime mesospheric Fe layer at midlatitudes. J Geophys Res 98:16,875–16,886View ArticleGoogle Scholar
- Kirkwood S, von Zahn U (1991) On the role of auroral electric fields in the formation of low altitude sporadic-E and sudden sodium layers. J Atmos Terr Phys 53:389–407View ArticleGoogle Scholar
- Kopp E (1997) On the abundance of metal ions in the lower ionosphere. J Geophys Res 102:9667–9674View ArticleGoogle Scholar
- Kwon KH, Senft DC, Gardner CS (1988) Lidar observations of sporadic sodium layers at Mauna Kea Observatory, Hawaii. J Geophys Res 93(14):199–14,208Google Scholar
- Makela JJ, Miller ES, Talaat ER (2010) Nighttime medium-scale traveling ionospheric disturbances at low geomagnetic latitudes. Geophys Res Lett 37(L24):104. doi:10.1029/2010GL045922 Google Scholar
- Mathews JD, Bekeny FS (1979) Upper atmosphere tides and the vertical motion of ionospheric sporadic layers at Arecibo. J Geophys Res 84:2743–2750View ArticleGoogle Scholar
- Mathews JD, Machuga DW, Zhou Q (2001) Evidence for electrodynamic linkages between spread-F, ion rain, the intermediate layer, and sporadic E: results from observations and simulations. JASTP 63:1529–1543Google Scholar
- Miller KL, Smith LG (1975) Horizontal structure of midlatitude sporadic-E layers observed by incoherent scatter radar. Radio Sci 10(3):271–276View ArticleGoogle Scholar
- Nagasawa C, Abo M (1995) Lidar observations of a lot of sporadic sodium layers in mid-latitude. Geophys Res Letts 22(3):263–266View ArticleGoogle Scholar
- Plane JMC, Cox RM, Rollason RJ (1999) Metallic layers in the mesopause and lower thermosphere region. Adv Space Res 24:1559–1570View ArticleGoogle Scholar
- Plane JMC (2003) Atmospheric chemistry of meteoric metals. Chem Rev 103:4963–4984View ArticleGoogle Scholar
- Plane JMC (2004) A time-resolved model of the mesospheric Na layer: constraints on the meteor input function. Atmos Chem Phys Discuss 4:39–69View ArticleGoogle Scholar
- Raizada S, Tepley CA (2002) Iron Boltzmann lidar temperature and density observations from Arecibo—an initial comparison with other techniques. Geophys Res Lett 29(12):1560View ArticleGoogle Scholar
- Raizada S, Tepley CA (2003) Seasonal variation of mesospheric iron layers at Arecibo: first results from low-latitudes. Geophys Res Lett 30:1082View ArticleGoogle Scholar
- Raizada S, Tepley CA, Janches D, Friedman JS, Zhou Q, Mathews JD (2004) Lidar observations of Ca and K metallic layers from Arecibo and comparison with micrometeor sporadic activity. J Atmos Sol Terr Phys 66:595–606View ArticleGoogle Scholar
- Raizada S, Tepley CA, Aponte N, Cabassa E (2011) Characteristics of neutral calcium and Ca+ near the mesopause, and their relationship with sporadic ion/electron layers at Arecibo. Geophys Res Lett 38:L09103. doi:10.1029/2011GL047327 View ArticleGoogle Scholar
- Raizada S, Tepley CA, Williams BP, Garcia R (2012) Summer to winter variability in mesospheric calcium ion distribution and its dependence on Sporadic E at Arecibo. J Geophys Res 117:A02303. doi:10.1029/2011JA01695 Google Scholar
- Rapp M, Lübken F-J (2004) Polar mesosphere summer echoes (PMSE): review of observations and current understanding. Atmos Chem Phys 4:2601–2633View ArticleGoogle Scholar
- Sarkhel S, Raizada S, Mathews JD, Smith S, Tepley CA, Rivera F, Gonzalez SA (2012) Identification of large scale billows-like structure in the neutral Na layer over Arecibo. J Geophys Res 117:A10301. doi:10.1029/2012JA017891 View ArticleGoogle Scholar
- Sarkhel S, Mathews JD, Shikha R, Sekar R, Chakrabarty D, Guharay A, Jee G, Kim J-H, Kerr RB, Geetha R, Sridharan S, Wu Q, Mlynczak MG, Russell JM, III (2015) A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India. Earth Planets Space 67:19. doi:10.1186/s40623-015-0183-5 View ArticleGoogle Scholar
- Sarkhel S, Mathews JD, Shikha R, Ramanathan S, Dibyendu C, Amitava G, Geonhwa J, Jeong-Han K, Kerr RB, Geetha R, Sundararajan S, Qian W, Mlynczak MG, Russell JM (2015b) Erratum to: A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India. Earth Planets Space 67:145. doi:10.1186/s40623-015-0276-1
- Seker I, Mathews JD, Wiig J, Guiterrez PF, Friedman JS, Tepley CA (2007) First results from the Penn State all sky imager at the Arecibo Observatory. Earth Planets Space 59:165–176View ArticleGoogle Scholar
- Sridharan S, Vishnu Prasanth P, BhavaniKumar Y, Geetha R, Sathishkumar S, Raghunath K (2009) Observations of peculiar sporadic sodium structures and their relation with wind variations. J Atmos Sol Terr Phys 71:575–582View ArticleGoogle Scholar
- Swider W (1996) Steady state D-region model, published in the book: Solar-Terrestrial Energy Proram (STEP). In: Schunk RW (ed) Handbook of ionospheric modelsGoogle Scholar
- Tepley CA, Mathews JD (1985) An incoherent scatter radar measurement of the average ion mass and temperature of a nighttime sporadic layer. J Geophys Res 90:3517–3519View ArticleGoogle Scholar
- Tepley CA, Mathews JD, Meriwether JW, Walker JCG (1981) Observations of the Ca+ twilight airglow from intermediate layers of ionization. J Geophys Res 86:7781–7786View ArticleGoogle Scholar
- Tepley CA et al (2003) First simultaneous observations of Ca+, K, and electron density using lidar and incoherent scatter radar at Arecibo. Geophys Res Lett 30(1):1009. doi:10.1029/2002GL015927 View ArticleGoogle Scholar
- Vondrak T, Woodcock KRS, Plane JMC (2006) Phys Chem Chem Phys 8:503View ArticleGoogle Scholar
- Wang J, Yang Y, Cheng X, Yang G, Song S, Gong S (2012) Double sodium layers observation over Beijing, China. Geophys Res Lett 39:L15801. doi:10.1029/2012GL052134 Google Scholar
- Whitehead JD (1989) Recent work on mid-latitude and equatorial Sporadic-E. J Atmos Terr Phys 51(5):401–424View ArticleGoogle Scholar
- Williams BP, Berkey FT, Sherman J, She C-Y (2007) Coincident extremely large sporadic sodium and sporadic E layers observed in the lower thermosphere over Colorado and Utah. Ann Geophys 25:3–8View ArticleGoogle Scholar
- Woodcock KR, Vondrak ST, Meech SR, Planew JMC (2006) A kinetic study of the reactions FeO+ + O, Fe+ N2 + O, Fe+. O2 + O and FeO+ + CO: implications for sporadic E layers in the upper atmosphere. Phys Chem Chem Phys 8:1812–1821. doi:10.1039/b518155k View ArticleGoogle Scholar
- Yi F, Zhang SD, Zeng HJ, He YJ, Yue XC, Liu JB, H FL, Xiong DH (2002) Lidar observations of sporadic Na layers over Wuhan (30.5° N, 114.4° N). Geophys Res Lett 29(9):1345. doi:10.1029/2001GL014353 View ArticleGoogle Scholar
- Yi F, Zhang S, Yue X, He Y, Yu C, Huang C, Li W (2008) Some ubiquitous features of the mesospheric Fe and Na layer borders from simultaneous and common-volume Fe and Na lidar observations. J Geophys Res 113:A04S91. doi:10.1029/2007JA012632 Google Scholar
- Yuan T, Wang J, Xuguang C, Sojka J, Rice D, Oberheide J, Criddle N (2014) Investigation of the seasonal and local time variations of the high-altitude sporadic Na layer (Nas) formation and the associated midlatitude descending E layer (Es) in lower E region. JGR. doi:10.1002/2014JA019942
- Yuan T, She C-Y, Kawahara TD, Krueger DA (2012) Seasonal variations of midlatitude mesospheric Na layer and their tidal period perturbations based on full diurnal cycle Na lidar observations of 2002–2008. J Geophys Res 117:D11304. doi:10.1029/2011JD017031 View ArticleGoogle Scholar
- Yue X, Zhou Q, Raizada S, Tepley CA, Friedman JF (2013) Relationship between mesospheric Na and Fe layers from simultaneous and common-volume lidar observations at Arecibo. J Geophys Res. doi: 10.1002/jgrd.50148.
- Zhou Q, Mathews JD, Tepley CA (1993) A proposed temperature dependent mechanism for the formation of sporadic sodium layers. J Atmos Sol Terr Phys 55(3):513–521View ArticleGoogle Scholar
- Zhou Q, Friedman J, Raizada S, Tepley CA, Morton YT (2005) Morphology of nighttime ion, potassium and sodium layers in the meteor zone above Arecibo. J Atmos Sol Terr Phys 67:1245–1257View ArticleGoogle Scholar
- Zhou Q, Raizada S, Tepley CA, Plane JMC (2008) Seasonal and diurnal variation of electron and iron concentrations at the meteor heights above Arecibo. J Atmos Sol Terr Phys 70:49–60. doi:10.1016/j.jastp.2007.09.012 View ArticleGoogle Scholar