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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]

• Na density inversion with narrowband filters for daytime measurement is discussed based on spectral analysis. • Annual mean diurnal variations of Na layer is obtained, showing considerable daytime bottom extension and nighttime top extension. • Large height-scale nighttime extension on Na layer topside shows obvious seasonal dependence, appearing frequently from early summer to autumn, while disappearing in winter months. • A case of nighttime Na layer top extension shows both gravity wave and tides signatures. Diurnal observations of metal Na layer can be implemented by making use of narrowband Faraday filters. On one hand, the narrowband spectral filters help to effectively suppress the background noise; on the other hand, the narrow bandwidth leads to different transmissions of Na layer resonance fluorescence signal and stratosphere Rayleigh scattering signal. The influence of the narrow spectral transmission on Na density retrieval cannot be canceled out by Rayleigh normalization and would result in a systematic error. In this paper, the Na density retrieval method when narrowband Faraday filters are used in the lidar receiver is discussed based on the transmission spectrum of Faraday filters and echo spectra of Rayleigh scattering and Na fluorescence. The results of Na layer diurnal variations that have been obtained from Na lidar observations at Beijing, China are presented. Considerable diurnal variation in Na density on the layer top and bottom are clearly revealed on a logarithmic scale. Intriguingly, larger height-scale nighttime extensions on the Na layer topside have been frequently observed from early summer to autumn. These observational results can provide valuable evidence for studying solar effect on the metal layer variation, atmospheric dynamical and chemical processes in the mesosphere and lower thermosphere region. [ABSTRACT FROM AUTHOR]

Based on long-term lidar (light detection and ranging) observations at Yanqing (40.5°N, 116°E) and Pingquan (41°N, 118.7°E), cloud events occurred in the vicinity of the stratopause above Beijing were reported for the first time. These events occurred with tenuous and sparse layers within the altitude range of 33–65 km, and the maximum VBSC value ranged from 1 × 10 − 10 m − 1 sr − 1 to 5.5 × 10 − 9 m − 1 sr − 1 . Considering temperature and water vapor measurements from SABER/TIMED, the occurrence mechanism of these lidar-observed cloud events was examined. It was found that some cloud layers resulted from the nucleation of water vapor due to the local meteorological changes in the middle atmosphere, while other lidar-observed clouds could comprise floating clusters of cosmic dust, hydrate droplets, volcanic ash, space traffic exhaust, etc. These cloud events are rare cloud-like phenomena in the middle atmosphere observed by lidars at midlatitudes in China; they differ from NLCs and PSCs in terms of altitude distribution and seasonal variation, and the relevant microphysics processes behind their occurrence are likely meaningful to meteorology at midlatitudes. [ABSTRACT FROM AUTHOR]

Based on observations from daytime lidars in eastern China, diurnal cycles of the sodium layer over Wuhan (30.5°N, 114.6°E) and Beijing (40.5°N, 116°E) are investigated. Diurnal variations of Na density, root mean square (RMS) layer width, and centroid height of the sodium layer are analyzed. Results reveal that the large diurnal cycles of the sodium layer are controlled mainly by 24-hr oscillations at the two observation sites. The diurnal variation of the sodium layer over Wuhan was modulated mainly by tidal perturbations during the lidar observation campaign. Conversely, the diurnal variation over Beijing was controlled principally by photoionization and photochemistry effects during another campaign, and there was little evidence of direct tidal perturbations. These comparisons suggest that the diurnal variation of the sodium layer perhaps has obvious regional characteristics across China. The variation can be either controlled mainly by tidal perturbations or by photoionization and photochemistry effects in different seasons. [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]

Sporadic sodium layers (SSLs) were studied with sodium (Na) lidar at Beijing (40.5°N, 116.0°E) and Haikou (19.5°N, 109.1°E) in China. The altitude distribution, strength factors, and occurrence time of SSL and sporadic E (E) layer events were statistically analyzed at both observing sites. SSL occurrence had a maximum near 22:00 local time, and E layer occurrence had a maximum before midnight. The altitude distributions of SSL and E layer events were better correlated at Haikou than at Beijing. All the average values of height and strength factor for SSL and E layer events, as well as the average of the maximum frequency that can be reflected by the E layer (fE), at Beijing were higher than those at Haikou. A better correlation between SSL and E layer events was also found at Haikou, and the formation of SSLs was considered to likely depend on the seasonal variability of chemical and dynamical processes. [ABSTRACT FROM AUTHOR]

• High Power-Aperture lidar system with two wavelengths and three channels for Rayleigh scattering, Mie scattering and Na fluorescence simultaneous detecting was completed at Beijing (Yanqing District, 40.3°N, 116.2°E). The excellent detecting performance of the lidar as photon counts shows a considerable high value of which the sodium layer echo peak value can reach to more than 37000 counts. • A relevant advanced lidar detecting standard has been realized. High resolution mode (15 m, 6.7 s) has been implemented while photo count per shot reaches to a considerable high value as 861, and the Power-Aperture Product can reach to 0.7 Wm2 which is equivalent to the largest LZT lidar (6-meter diameter, 5 w power, 1500 photocount per shot, 0.6 Wm2 at UBC, Canada), ALO (1000 photocount per shot 0.6 Wm2 at Cerro Pachón, Chile) and STAR (Boulder, Colorado US) lidar as their high level standard at the moment. • Based on this High Power-Aperture lidar, the first report of observations of turbulence spectrum in North hemisphere over China was provided, which had been extremely difficult to be observed due to the resolution and the signal/noise rate as in before for most researches. The observed turbulence spectrum was found in consistent with the only report by ALO lidar at Chile in South hemisphere observed in 2017 [Y. Guo et. al., Geophys.Res.Lett., 2017 ] and well fitted with the theory prediction, which can effectively help us to further understand the entire global gravity wave behavior. With the support of the Meridian Project of China, an integrated two-wavelength and three-channel lidar system was completed for atmospheric detection in Yanqing, Beijing. This lidar system emitted a 589 nm laser beam for detecting the 80–110 km sodium atomic layer. A 532 nm laser system was used to detect the 30–80 km atmospheric temperature and density and also to provide the atmosphere aerosol information from the ground to a height of 30 km. Because all of the technique details were carefully designed, this lidar obtained a very good signal and achieved the full-scale detection of the atmosphere from near-ground to a height of 110 km. With the conventional mode (3 minutes, 100 m), the atmospheric 532 nm Rayleigh detecting channel could reach a height of 80 km, and the 589 nm channel photo counting peak could reach 37000. This specification actually reached the high power-aperture sodium lidar standard in advance, which caused the high-resolution detection mode (15 m, 6.7 s) to be realized. For the high-resolution detecting mode of our Yanqing Lidar, observations of the spectrum of a gravity wave in the turbulence region were given according to the advantages of the high signal/noise ratio. Additionally, the properties of the turbulence spectrum and their variations were first obtained in the northern hemisphere over China. The observed gravity wave turbulence spectra well fitted with the theoretical prediction. These results achieved new field detections, which will lead us to further discover the nature and essence of a gravity wave and deeply study the behavior of upper atmosphere circulation on a large scale. [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]

Sporadic sodium layers (SSLs) have been observed all over the globe and always has been of great concern. However, most researches on SSLs are based on only nocturnal observations due to strong daytime solar background noise, thus there is still insufficient understanding of the diurnal variation of SSLs. In this paper, a statistical analysis of SSLs observed by a diurnal sodium (Na) lidar at Beijing (40.5 ° N, 116 ° E) from April 2014 to December 2016 has been reported. A total of 54 and 87 events that peaked during daytime and nighttime, respectively, are identified. The average occurrence interval for daytime observations is ~36 h per SSL, which is slightly longer than the value of ~29 h per SSL for nighttime observations. Both daytime and nighttime SSLs show evident seasonal variations with summer SSLs occurring much more frequently and tending to appear at higher altitude with lower peak density while larger strength factor. The seasonal dependence of SSL occurrence is consistent with that of sporadic E (Es) occurrence, however, their diurnal variations are found to be totally different. The SSLs are observed more frequently around 03–04 LT during nighttime and 16–17 LT during daytime when Es layers appear at lower altitudes (below 110 km), while have a lowest occurrence rate around midday when Es layers occurrence rate peak. The average peak altitude of SSLs during the second half of the night is lower compared to that during the first half of the night. Around midday, the average peak width of SSLs is narrower and peak density tends to be smaller when compared to those at other times. The possible explanations for the diurnal and seasonal variations of SSLs characteristics are discussed, and the key role of the evolution of Es layer height modulated by semidiurnal tide in the local time variation of SSL is highlighted. • The occurrence rate of daytime SSLs has a similar seasonal dependence to those of nighttime SSLs as well as Es. • SSLs occurred more frequently around 03–04 LT during nighttime and 16–17 LT during daytime, while rarely around midday. • Both daytime and nighttime observations SSLs tend to have higher peak altitude, larger strength factor, lower peak density in summer. • Diurnal variation of SSL occurrence is related to tidal-modulated Es height and photochemistry and ionization reactions. [ABSTRACT FROM AUTHOR]

Based on application of the atomic filter technology in a signal detection system of lidar, the diurnal observation of sodium lidar were obtained using the system at the National Space Science Center of the Chinese Academy of Sciences at Beijing Yanqing station (40.5° N, 116° E) in April 2014. During the lidar observation period, among the 103 cases of continuous daytime observations, the longest time was 181 h. In the case of a continuous observation period of 5 days (13–18 October 2014), the signal-to-noise ratio reached to 19:1 at 12:00–13:00 Local Time of the daytime, when the spatial and time resolutions were respectively set to 96 m of 167 s. The improvements resulted in the highest detection level of any existing diurnal lidars in China. Some interesting phenomena such as the sporadic sodium layer have also been observed during the daytime. The daytime capability extended the observing time range of the earlier systems that were limited to only nighttime observations. This innovation provides a useful method for the studies of diurnal tides, photochemistry, gravity waves, and correlative modeling studies. [ABSTRACT FROM AUTHOR]