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Lidar observations of metal layers play a significant role in research on the chemistry and dynamics of the mesosphere and lower thermosphere. This work reports on Fe lidar observations conducted in Beijing and Mohe. Utilizing the same laser emission system, a 1064 nm seed laser was injected into an Nd: YAG laser to generate a single longitudinal-mode pulse 532 nm laser, which pumped a dye laser to produce a 572 nm laser. The 572 nm laser and the remaining 1064 nm fundamental frequency laser passed through a sum–frequency module to generate a 372 nm laser to detect the Fe layer. According to a total of 52.6 h of observations for 10 nights in Beijing, the Fe layer has an average column density of 1.24 × 1010 cm−2, an RMS width of 4.4 km and a centroid altitude of 89.4 km. In Mohe, observed for 16 nights and a total of 91.5 h, the Fe layer has an average column density of 1.08 × 1010 cm−2, an RMS width of 4.6 km and a centroid altitude of 89.5 km. The probability of the occurrence of sporadic Fe layers was 42.4% in Beijing and 29.4% in Mohe. Compared to simultaneously observed Na layers, the occurrence probabilities of sporadic Fe layers were higher than those of sporadic Na layers in both stations. Based on the two cases observed in Beijing, it is conjectured that the formation mechanism of sporadic metal layers above approximately 100 km has a more significant influence on sporadic Fe layers than on sporadic Na layers. The lower thermospheric Fe layers with densities significantly larger than those of the main layer were observed during two nights in Mohe. This work contributes to the refinement of the global distribution of Fe layers and provides abundant observational data for the modeling and study of the metal layers. [ABSTRACT FROM AUTHOR]

In March 2020, an all-solid-state dual-wavelength narrow-band lidar system was deployed. A total of 226 nights spanning from March 2020 to July 2022 were employed in order to investigate the seasonal variations of calcium atoms and ions in the mesosphere over Beijing (40.41°N, 116.01°E). The Ca+ layer shows general annual variation, while a semiannual variation is observed on the Ca layer. The calcium atomic column densities ranged from 2.0 × 106 to 1.1 × 108 cm−2, and the calcium ion column densities ranged from 1.6 × 106 to 4.2 × 108 cm−2. The mean centroid heights of Ca+ and Ca are 98.6 km and 93.0 km, respectively, and the centroid heights of Ca+ and Ca are mostly influenced by annual variations. The seasonal variation in the Ca+ and Ca layers in Beijing exhibits similarities to that of Kühlungsborn (54°N). While the peak density of Ca+ in Beijing are similar to those observed in Kühlungsborn, the peak density of the Ca layer in Beijing is about half of that reported in the Ca layer at 54°N. We provide an explanation for the disparities in the column abundance and centroid altitude of the Ca layer between Yanqing and Kühlungsborn, discussing variations in neutralization among different metal ions. [ABSTRACT FROM AUTHOR]

Resonance fluorescence scattering is the physical mechanism with which lidar detects atmospheric metal layers. The resonance fluorescence scattering cross section is an important parameter for lidar data processing. In this work, the resonance fluorescence backscattering cross sections of most detectable metal atoms and ions in the atmosphere were calculated. The calculated maximum backscattering cross section of Na at the D2 line is 7.38 × 10−17 m2/sr; K at the D1 line is 7.37 × 10−17 m2/sr; Fe at the 372 nm line is 7.53 × 10−18 m2/sr; Fe at the 374 nm line is 6.98 × 10−18 m2/sr; Fe at the 386 nm line is 3.75 × 10−18 m2/sr; Ni at the 337 nm line is 4.05 × 10−18 m2/sr; and Ni at the 341 nm line is 2.05 × 10−17 m2/sr; Ca is 3.06 × 10−16 m2/sr; Ca+ is 1.12 × 10−16 m2/sr. The influence of the laser linewidth on the effective scattering cross section was discussed. If the laser linewidth is lower than 2 GHz to detect Na, the laser center frequency locked at the D2a line is a better option than the D2 line in order to obtain greater signals. If an unlocked lidar is used to detect Na, the frequency at D2a should be used as the laser center frequency when the effective scattering cross section of Na was calculated, because the absorption cross section of Na atom has two local maxima. This work proposes a quantifiable comparative method for assessing the observation difficulty of different metal particles by comparing their relative uncertainties in lidar observation. It is assumed that under the same observation conditions, the detectability of different metal atoms and ions is compared. Using Na as a basis for comparison, the relative uncertainty of Ni at 337 nm is the highest, about a factor of 21 larger than that of Na, indicating that it is the most difficult to be detected. The purpose of this work is to present a quantifiable comparison method for the detection difficulty of the metal particles by lidar in the middle and upper atmosphere, which has great significance for the design of the lidar system. [ABSTRACT FROM AUTHOR]

Based on the established LIDAR chain along the 120°E meridian in China, the gravity wave (GW) activity between 80 and 105 km and the seasonal behavior of temporal and spatial spectra at Beijing, Hefei and Hainan were studied with three years of continued observations. The averaged GW-induced atmospheric density perturbations are near 6%, which in summer are obviously larger than in winter. The semiannual maxima occur near the solstice and the minimum emerges around the equinox at different latitudes. Besides, as a disparity, the density perturbation of GW is still active considerably in winter at low latitude at Hainan. The spectra of vertical wave number Fa(m) and observed frequency Fa(ω) show power law shapes, of which the average is near −3 and −1.7, respectively, and both spectra with special values all exhibit similar seasonal behavior as the atmospheric density perturbations shows. This behavior is explained by multiple effects possibly originating from Tibet plateau (TP) and the main GW source in China was roughly calculated by the LIDAR observation method for the first time located at the TP boundary. [ABSTRACT FROM AUTHOR]

We report a world record of lidar profiling of metallic Ca+ ions up to 300 km in the midlatitude nighttime ionosphere during geomagnetic quiet time. Ca+ measurements (∼80–300 km) were made over Beijing (40.42°N, 116.02°E) with an Optical‐Parametric‐Oscillator‐based lidar from March 2020 through June 2021. Main Ca+ layers (80–100 km) persist through all nights, and high‐density sporadic Ca+ layers (∼100–120 km) frequently occur in summer. Thermosphere‐ionosphere Ca+ (TICa+) layers (∼110–300 km) are likely formed via Ca+ uplifting from these sporadic layers. The lidar observations capture the complete evolution of TICa+ layers from onset to ending, revealing intriguing features. Concurrent ionosonde measurements show strong sporadic E layers developed before TICa+ and spread F onset. Neutral winds can partially account for observed vertical transport but enhanced electric fields are required to explain the results. Such lidar observations promise new insights into E‐ and F‐region coupling and plasma inhomogeneities. Plain Language Summary: Inhomogeneities (also called irregularities) in the ionospheric plasma distribution can significantly degrade satellite communications and negatively impact Global Positioning System‐based navigation systems that rely on the trans‐ionospheric radio‐wave propagation. Understanding the formation mechanisms of, thus predicting, ionospheric inhomogeneities is still a huge challenge in space weather research. Long‐lived meteoric metal ions (≫ $\gg $1 day above 100 km altitude) converge to form dense ion layers, causing plasma irregularities in the ionosphere. Therefore, it is imperative to observe and understand the transport and formation of metallic ion layers. However, it is technically challenging to detect specific ion species, especially tracing ion transport over large vertical ranges and time durations. Numerous instruments detect electron density but cannot distinguish ion species. Rocket‐borne mass spectrometers can distinguish ion species but provide only snapshots. Lidars provide a powerful tool to profile and trace metallic species over extended periods by exciting specific resonance fluorescence. The only metal ions detectable by ground‐based lidars are Ca+, and previous lidar measurements reached ∼180 km. Our Ca+ lidar upgraded with narrowband lasers has achieved high detection sensitivity, enabling the Ca+ profiling up to 300 km. Such lidar measurements of dynamical Ca+ layers open a new window to study plasma irregularities. Key Points: First lidar profiling of Ca+ ions from ∼80 to 300 km was made over Beijing in the nighttime ionosphere during geomagnetic quiet timeThermosphere‐ionosphere Ca+ layers (∼10 s cm−3) are likely formed by uplifting ions from sporadic Ca+ at ∼110 km & show complex structuresSpread F occurs concurrently with Thermosphere‐ionosphere Ca+ & strong sporadic E layers occur before the onset of TICa+ and spread F, suggesting E‐ and F‐region coupling [ABSTRACT FROM AUTHOR]

A double-laser-beam lidar was successfully developed in 2010 to measure the K layer over Yanqing County, Beijing (40.5°N, 116.2°E). Comprehensive statistical analyses of sporadic K (Ks) layer parameters were conducted using two years of lidar data, and the parameters of the Ks layers and their distribution obtained by the analyses are described. The seasonal distribution of Ks occurrence was obtained, with two maxima observed in January and July, respectively. The seasonal distributions of sporadic E (Es) occurrence over Beijing differ from those of Ks occurrence. However, good correlations between Es and Ks in case by case study were found. We also found that four Ks events with peak altitudes lower than 90 km were associated with large and sharp temperature increases in five comparative examples. [ABSTRACT FROM AUTHOR]

Beijing Na–K lidar has been started running in 2010. This lidar has two laser beams: one dye laser emits a 589-nm laser beam for Na layer detection; the other dye laser emits a 770-nm laser beam for K layer detection. Under similar conditions, the echo signal of K layer is only about 2 orders of magnitude smaller than that of Na layer. This lidar has a sufficient Signal Noise Ratio (SNR). The structure and details of potassium layer can be effectively distinguished from a single original echo. Several examples of co-observation of density of Na and K layer showed some different results with previous studies. This lidar not only can supplement the lack of Na and K layer observation at this latitude region, but also provide evidence for the atmospheric sciences and space environment monitoring. [ABSTRACT FROM AUTHOR]