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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]

Based on the resonance fluorescence scattering mechanism, a narrowband sodium (Na) lidar can measure temperature and wind in the mesosphere and lower thermosphere (MLT) region. By using a narrowband spectral filter, background light noise during the day can be suppressed, allowing for continuous observations. To obtain full-diurnal-cycle temperature and wind measurement results, a complex and precise retrieval process is required, along with necessary corrections to minimize measurement errors. This paper introduces the design of a data acquisition unit for three frequencies in three directions of the Na lidar system in the Chinese Meridian Project (Phase II) and investigates the calibration and retrieval methods for obtaining diurnal temperature and horizontal wind in the MLT region, using a Na Doppler lidar with Faraday anomalous dispersion optical filter (FADOF). Furthermore, these methods are applied to observations conducted by a Na lidar in Beijing, China. The wind and temperature results over full diurnal cycles obtained from the all-solid-state Na Doppler lidar are reported for the first time and compared with temperature measurements from satellite, as well as wind observations from a meteor radar. The comparison demonstrates a reasonable agreement between the results, indicating the rationality of the lidar-retrieved results and the feasibility and effectiveness of the data correction and retrieval method. [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]