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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]

A prediction system was developed to determine the maximum Rayleigh altitude (MRA) by improving the automated detection of LIDAR power-on conditions and adapting to advancements in middle- and upper-atmosphere LIDAR technology. The proposed system was developed using observational data and nighttime sky imagery collected from multiple LIDAR stations. To assess the accuracy of predictions, three key parameters were employed: mean square error, root mean square error, and mean absolute error. Among the three prediction models created through multivariate regression and autoregressive integrated moving average (ARIMA) analyses, the most suitable model was selected for predicting the MRA. One-month predictions demonstrated the accuracy of the MRA with a maximum error of no more than 5 km and an average error of less than 2 km. This technology has been successfully implemented in numerous LIDAR stations, enhancing their automation capabilities and providing key technical support for large-scale, unmanned, and operational deployments in the middle- and upper-atmosphere LIDAR systems. [ABSTRACT FROM AUTHOR]

Equipped with a 1-meter Cassegrain telescope with 6.2 meter focal length and an electronically gated Intensified Charge-Coupled Device (ICCD), a multilayer Na imager is designed and developed at Wuhan in China. This novel instrument has successfully achieved the first preliminary 3-D image of the mesospheric Sodium (Na) layer when running alongside a Na lidar. The vertical Na layer profile is measured by the lidar, while the horizontal structure of the layer at different altitudes is measured by the ICCD imaging with a horizontal resolution of ~3.7 urad. In this experiment, controlled by the delay and width of the ICCD gating signal, the images of the layer are taken with three-second temporal resolution for every 5 km. The results show highly variable structures in both the vertical and horizontal directions within the Na layer. Horizontal images of the Na layer at different altitudes near both the permanent layer (80–100 km) and a sporadic Na layer at 117.5 km are obtained simultaneously for the first time. The Na number density profiles measured by the lidar and those derived from this imaging technique show excellent agreement, demonstrating the success of this observational technique and the first 3-D imaging of the mesospheric Na layer. [ABSTRACT FROM AUTHOR]

The transmission spectrum of a narrow-band interference filter is crucial and highly influenced by factors such as the temperature and angle, thus requiring precise and online measurements. The traditional method of measuring the transmission spectrum of an interference filter involves the use of a spectrometer, but the accuracy of this method is limited. Moreover, placing a narrow-band interference filter inside a spectrometer hinders real-time online measurements. To address this issue, there is demand for high-precision online spectral testing methods. In response to this demand, we propose and experimentally validate a fine spectral characterization method for narrow-band interference filters. This method uses a narrow-linewidth tunable laser, achieving a spectral resolution in the MHz range for online testing. Two types of narrow-band interference filters were tested using the constructed laser spectroscopy experimental system, obtaining a transmission spectrum with a spectral resolution of 318 MHz. In comparison to spectrometer-based methods, our proposed method demonstrates higher spectral accuracy, enables online measurements, and provides more accurate measurements for special spectral interference filters. This approach has significant application value and promising development prospects. [ABSTRACT FROM AUTHOR]

We report an all-solid-state narrowband lidar system for the simultaneous detection of Ca and Ca+ layers over Yanqing (40.41°N, 116.01°E). The uniqueness of this lidar lies in its transmitter, which is based on optical parametric oscillation (OPO) and optical parametric amplification (OPA) techniques. The injection seeded OPO and the OPA are pumped by the second harmonic of an injection-seeded Nd:YAG laser, which can generate coherent light at the wavelength of 786 nm or 846 nm lasers, whose second harmonics in turn generate the 393 nm or 423 nm pulses, respectively, for the detection of thermospheric and ionospheric Ca+ and Ca layers. Compared to the conventional dye-based system, this lidar transmitter is a narrowband system (bandwidth < 200 MHz), which has produced a factor of two more output power with higher stability and reliability. The lidar system in Yingqing demonstrated Ca+ detection sensitivity of 0.1 atoms-cm−3 for long-term observation and reached a height of ~300 km. Potential applications and further improvements in this lidar technique are also discussed in this paper. [ABSTRACT FROM AUTHOR]

We present the first simultaneous observation of mesopause sodium (Na) and potassium (K) layer by a lidar which has Na and K channel simultaneously at the South Hemisphere site, São José dos Campos (23.1°S, 45.9°W). Measurements reported here were conducted on two nights with 3.5 and 8 h of observations in November 2016. On 20 November 2016, sporadic layers in both Na and K layer occurred above 100 km, and the higher layers corresponded well with sporadic E (Es) layer. And the density of Na at 100–105 km is higher than that at main layer around 90 km, but K density around 100 km is at least 3 times smaller compared with the K density around 90 km for the similar period. On 21 November 2016, both sporadic layers occurred in main layer height with obvious descending variations with time, which seems like tidal induced. Notably, the peak K/Na ratio slowly increased with time. And Na layer and K layer showed different processes along with time with K density reaching its maximum 1 h later than that of Na. Correlations of Na/K density, Es, and winds were also discussed. [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 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]

In 2011, Chu et al. reported the observation of neutral Fe layers reaching 155 km. Since then, there are five additional reports of layers extending above 130 km to as high as 170 km, none from central middle latitudes (35°–55°), a large atmospheric region of considerable importance. Here we report the first concurrent observations of thermospheric Na layers from two nearby lidar stations so located, Yanqing (40.5°N, 116.0°E) and Pingquan (41.0°N, 118.7°E). From one‐year data set, we found four such layers, including an unprecedented one reaching 200 km with highest density of 35 cm−3 and fastest descending rate. While the main Na layers were comparable, in three nights, these thermospheric layers were observed only in one station (Yanqing), suggesting that these layers often occur locally with a horizontal scale less than ~250 km. We tabulate, compare, and discuss the principle characteristics of all the reported thermospheric layers. Plain Language Summary: The neutral Na atomic layers are mainly distributed from 80 to 105 km and they have been used as tracers to study atmospheric chemistry and dynamical processes. Based on four thermospheric Na layers above 130 km observed by two central middle‐latitude lidar stations simultaneously, the paper analyzes the horizontal dimension of the observed thermospheric Na layers, and reports an unprecedented layer reaching an altitude of 200 km with a peak density of 35 cm−3 and a descending rate of 9.3 m/s. The fact high peak density is possible around 150 km opens up the potential for tripling the altitude range for probing temperature and wind by a resonance fluorescence lidar, thus advancing our understanding of dynamics and chemistry in the upper atmosphere. Key Points: The first report of thermospheric Na layers above 130 km over central middle latitudesThe unprecedented thermospheric Na layer that reached highest altitude (200 km), Na density (35 cm−3), and descending speed (9.3 m/s)The first concurrent observation of thermospheric layers from two stations, revealing 3/4 cases with horizontal dimension within ~250 km [ABSTRACT FROM AUTHOR]

A combined lidar system on the basis of conventional Rayleigh lidar has been extended by two rotational Raman (RR) channels for nocturnal atmospheric temperature measurements from 5 to 80 km over Wuhan, China (30.5°N, 114.5°E). An overlapping altitude range of about 10 km is obtained with the RR-technique temperatures reaching upward to 40 km and the Rayleigh-integration-technique temperatures above 30 km. Temperature values obtained by two different mechanisms match nicely in the overlapping area. By using a data-merge method, complete temperature profiles covering widely from 5 to 80 km are obtained for the observation of the thermal structure and perturbations from the troposphere up to the mesosphere. Based on the overlapping-region (30–40 km) data obtained from this combined RR–Rayleigh lidar system and Rayleigh-integration-technique temperatures initialized with model data at an upper height (90 km), we develop a self-calibration method for the determination of the system-dependent constants for RR temperature retrieval. Compared with the conventional radiosonde calibration method, the self-calibration obtained in the overlap region of both lidar temperature measurement techniques can be extrapolated to the lower temperatures in the tropopause region by using the simpler two-constant calibration function. With this new calibration method, the combined lidar system can perform independent and accurate atmospheric temperature measurements when a coincident (in time and space) radiosonde is not available, as it is often the case. This combined RR–Rayleigh lidar thus has the potential for long-term studies of atmospheric thermal structure and associate perturbations. [ABSTRACT FROM PUBLISHER]

The low thermospheric sodium layer (LTSL) is the separate sodium atom layer above 105 km. Based on 11,607 h of lidar observations from Yanqing (40.5° N, 116.0° E) from 2010 to 2016, we found 38 LTSLs wherein the peak densities were more than five percent above those of the main sodium layers. This work presents the peak altitudes, peak local times and peak densities of the LTSLs as well as the long-term characteristics of the seasonal and inter-annual variations of LTSLs. We analyzed the correlation between the LTSL and sporadic E layer (Es). The seasonal variation trends of the occurrences of LTSL and Es are similar, and the results showed that 95% of the LTSLs were accompanied by Es. We also found that 69% of the LTSL cases exhibited apparent downward phase progressions, while the descending rates of the LTSLs are consistent with the phase speeds of the tide. [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]

In the above paper [1], there are two errors on page 7058. In addition, the support information has been updated to include an additional funding source. The complete funding statement should be: [ABSTRACT FROM PUBLISHER]