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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 present an analysis of the response of quasi-10-day waves (Q10DWs) to the sudden stratospheric warming (SSW) event which occurred on March 23, 2020. The Q10DWs are observed in the mesosphere and lower thermosphere (MLT) region by three meteor radars, which are located at middle latitudes along the 120°E meridian from Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), to Wuhan (WH, 30.5°N, 114.6°E). The Q10DWs reveal similar temporal and altitudinal variations during the SSW in the MLT region at the three stations. The activities of Q10DWs are also captured in the temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite in the MLT region. Further analysis of the Q10DW phases indicates that the Q10DWs might be in situ generated due to mesospheric instabilities at higher latitudes around MH and then propagate southward to lower latitudes at BJ and WH. The atmospheric instabilities are not directly responsible for the excitations of Q10DWs at lower latitudes, while the observed equatorward propagation of the Q10DWs is important. Our result provides the observational evidence for latitudinal couplings in the MLT region after the SSW onset, which is achieved by southward propagating planetary waves in the MLT region. [ABSTRACT FROM AUTHOR]

Based on the full-diurnal-cycle sodium (Na) lidar observations at Beijing (40.41 ∘ N, 116.01 ∘ E), we report pronounced downward extensions of the Na layer bottomside to below 75 km near mid-December 2014. Considerable Na atoms were observed even as low as ∼ 72 km, where Na atoms are short-lived. More interestingly, an unprecedented Na density of ∼ 2500 atoms cm -3 around 75 km was observed on 17 December 2014. Such high Na atoms concentration was 2 orders of magnitude larger than that normally observed at the similar altitude region. The variations of Na density on the layer bottom were found to be accompanied by warming temperature anomalies and considerable perturbations of minor chemical species (H, O, O 3) in the upper mesosphere. Different from the previous reported metal layer bottom enhancements mainly contributed by photolysis after sunrise, these observational results suggest more critical contributions were made by the Na neutral chemical reactions to the Na layer bottom extensions reported here. The time–longitudinal variations of background atmospheric parameters in the upper mesosphere and stratosphere from global satellite observations and ERA reanalysis data indicated that the anomalous structures observed near the lidar site in mid-December 2014 were associated with planetary wave (PW) activities. The anomalies of temperature and O 3 perturbation showed opposite phase in the altitude range of 70–75 and 35–45 km. This implied that the vertical coupling between the mesosphere and stratosphere, possibly driven by the interactions of PW activities with background atmosphere and modulation of gravity wave (GW) filtering by stratospheric wind, contributed to the perturbations of background atmosphere. Furthermore, the bottom enhancement on 17 December 2014 was also accompanied by clear wavy signatures in the main layer. The strong downwelling regions are likely due to the superposition of tide and GW, suggesting the wave-induced adiabatic vertical motion of the air parcel contributed greatly to the formation of the much stronger Na layer bottom enhancement on 17 December 2014. These results provide a clear observational evidence for the Na layer bottom response to the planetary-scale atmospheric perturbations in addition to tide and GW through affecting the chemical balance. The results of this paper also have implications for the response of the metal layer to vertical coupling between the lower atmosphere and the mesosphere. [ABSTRACT FROM AUTHOR]

Based on the long‐term observations of the Wuhan and Beijing Mesosphere‐Stratosphere‐Troposphere (MST) radars, the statistic characteristics of the mesospheric vertical winds at midlatitudes are investigated for the first time. The vertical wind data come from the Wuhan MST radar (29.51°N, 114.13°E) during 2012–2017 and from the Beijing MST radar (39.75°N, 116.96°E) during 2012–2014. The subdaily, seasonal, and annual variations of the mesospheric vertical winds at Wuhan and Beijing are presented. No obvious subdaily and seasonal variations are found and the annual variations of the mean vertical winds are downward in most of time. The mean vertical winds at Wuhan become smaller in summer and turn to upward at some heights, while those of Beijing only become smaller in summer. The difference of summer vertical winds over Wuhan and Beijing is closely related to the gravity wave activity. The Wuhan MST radar is located to the east side of the Qinghai‐Tibet plateau and also in the East Asian monsoon region, thus the mesospheric winds over Wuhan may experience more influence of gravity waves compared with those over Beijing. The possible bias sources in the vertical wind measurement of the two MST radars are carefully analyzed and the presented wind velocities are proved to be credible. The measured velocity magnitude is similar to other Very High Frequency radar observations, but much larger than that of the WACCM simulation. The Stokes drift, multicellular circulation structures, the wave influence on the radar echoes are raised as the potential sources for this discrepancy. Key Points: Wuhan and Beijing MST radars are used to study the statistical characteristics of the midlatitude mesospheric vertical windsEstimated mesospheric vertical winds at Wuhan and Beijing are generally downward all the year, and much larger than the model dataMuch more gravity wave activities are responsible for the summer difference of the mesospheric vertical winds [ABSTRACT FROM AUTHOR]

In this study, we employed the non-uniform rational B-splines surface technique to develop a provisional horizontal wind model of the mesosphere and lower thermosphere at altitudes of 87, 97, and 250 km over Kelan (38.7°N, 111.6°E) in China using Fabry–Perot interferometer (FPI) observations for the period between January 2012 and May 2014. We compared the meridional and zonal winds derived from the Kelan FPI wind model with those based on Meteor Radar wind observations at Beijing (39.92°N, 116.39°E), and those calculated from horizontal wind models, i.e., HWM93 and HWM07, at Kelan. Our analysis showed the following. (1) At 87 and 97 km, the Kelan FPI wind patterns exhibited strong annual variation in the meridional wind and semiannual variation in the zonal wind, as well as diurnal variation, which was dominated by a semidiurnal tidal variation in the meridional and zonal winds during May and September with a diurnal phase difference. The Kelan FPI wind patterns agreed well with the Meteor Radar winds and the HWM07 model results, but less well with the HWM93 model. (2) At 250 km, the FPI wind patterns agreed fairly well with the HWM93 results, where both indicated annual/diurnal variation in the meridional and zonal winds, and weak semidiurnal tidal variation. There were large discrepancies between the Kelan FPI winds and the HWM07 model results, which were mainly due to differences in the annual variation in the nighttime meridional wind. (3) The magnitude of the FPI winds was comparable to the HWM93 results but they were nearly 40–50% lower than the other winds, which is attributable to the inherent limitations of airglow measurement. Thus, this local empirical wind model could be used to investigate the climatological features of local ionospheric spatial–temporal variations. [ABSTRACT FROM AUTHOR]

• A new Ni lidar has been designed and deployed at Yanqing station. This lidar has three advantages: first, the lidar employs 532 nm laser light to pump a near-IR laser dye with a high conversion efficiency and long life (dye replacement every 36 hours), which is much better suited to long-term observations; second, frequency doubling the IR laser beam avoids disturbances by receiving backscatter of Amplified Spontaneous Emission (ASE) of the dye laser.; third, this new Ni lidar makes use of narrow bandwidth interference filters. The narrow bandwidth filters better discriminate against background light. • The lidar measurements of Nickel layers have been made in Yangqing from 3 April to 31 December 2019 (25 days in total). This demonstrates the stability of the lidar for making continuous Ni measurements over an extended period, enabling the first investigation of night-time and seasonal density variation of the Ni layer. The Ni density results are similar to that reported by Gerding et al. [2018] and the WACCM-Ni model [Daly et al., 2020]. • For the first time, we used the high altitude Ni lidar to determine the branching ratios of three different optical transition from Ni in the 3d9(2D)4s3D3 state (excited at 341 nm), and showed that these branching ratios are very close to the theoretical values. Ni atoms, produced in the Earth's upper atmosphere by meteoric ablation, are challenging to measure by lidar because the Ni atom density is low, the resonance scattering cross section is relatively small, and the transitions occur in the near-UV around 340 nm where absorption by the stratospheric ozone layer starts to become significant. A new Ni lidar has been designed and deployed at Yanqing station (4 0 ∘ N , 11 6 ∘ E) Beijing, China over the period from 3 April 2019 to 31 December 2019. The combination of a frequency-doubled near-IR laser and narrow bandwidth filters enables stable and continuous operation. From 25 nights of measurements, the Ni peak density ranges from 98 to 460 cm−3 with the peak altitude between 80 and 88 km; the average peak density is 258 ± 115cm−3. The average column abundances of Nickel varied between 1.52 × 108 and 6.0 × 108 cm−2 between mid-summer and mid-winter. An experiment was also carried out using the Ni lidar to determine the spectroscopic branching ratios from the excited Ni(3F 4) state into 3 lower states; very close agreement with the literature values were obtained. [ABSTRACT FROM AUTHOR]

It is well known that gravity waves play an important role in determining the atmospheric circulation. The breaking of the gravity wave also contributes to the production of turbulence. Atmospheric gravity waves are also believed to have a significant impact on climate. Among the variety of techniques, MST (Mesosphere-Stratosphere-Troposphere) radar is a great tool for studying atmospheric dynamics, and it plays a unique role in gravity wave investigations. Since 2011, the Beijing MST radar (one of the only two domestic MST in China, within the Chinese Meridian Project) has been in continuous operation observing the vertical distribution of three-dimensional winds and turbulence in the troposphere-lower stratosphere and mesosphere-lower thermosphere regions with high spatial and temporal resolutions. Using one year's data from the Beijing MST radar observed in 2012, a statistical analysis is made to investigate inertia-gravity waves (IGWs) characteristics in troposphere and lower stratosphere. A combination of the Lomb-Scargle spectral analysis, the quasi-monochromatic gravity waves model, and the hodograph method were used to investigate wave characteristics including intrinsic frequencies, vertical wavelengths, horizontal wavelengths and period. The characteristics of IGWs show difference in troposphere and lower stratosphere. The gravity waves energy is consistent with the variation of the horizontal wind disturbance intensity. In addition, the monthly averaged IGWs occurrence rate indicates that the IGWs occur mostly in summer, which is related to the dynamic instability excitation; while in the lower stratosphere the occurrence is large in winter, which is closely related to the vertical shear of the horizontal wind. [ABSTRACT FROM AUTHOR]