In this paper, we present comprehensive night-time seeing statistics at the Lenghu site using data collected between 2018 and 2021 using a differential image motion monitor. The results show that the median seeing is 0.80 arcsec, which slightly larger than that previously reported due to climate change. Additionally, we investigated the annual, seasonal, and monthly seeing statistics, as well as possible hourly seeing trends in each season. The results demonstrate that the seeing at the Lenghu site is very stable, with monthly median seeing varying from 0.6 arcsec to 0.95 arcsec. The seasonal dependence of seeing shows obvious variations over different years. The best year of seeing was 2019 (0.74 arcsec), and the best seeing occurred in spring (0.68 arcsec) to early summer (June, 0.63 arcsec), while the worst seeing occurred in winter (0.80 arcsec). The minimum seeing value throughout the night is at approximately three hours before dawn. Furthermore, wind speed profiles, especially V₂₀₀ (particularly the wind speed at 200 mbar), are important parameters for evaluating astronomical sites in terms of their suitability for adaptive optics. We first show the complete monthly average behaviours of the wind speed profile and V₂₀₀ using the European Center for Medium-Range Weather Forecast reanalysis datasets. The results demonstrate the annual periodicity and variability of V₂₀₀, and the yearly V₂₀₀ modulation function is also provided. V₂₀₀ maintains large values throughout the autumn (average:35.01 m/s) and winter (average:34.33 m/s), while the minimum V₂₀₀ occurs in spring (average:27.93 m/s).

This paper presents a comprehensive site survey of the Delingha site on the northern Tibetan Plateau from 2012 to 2014. In this campaign, we investigated 24 h continuous astronomical seeing, meteorological properties, and |$C_{n}^{2}$| in the ground layer (GL). The results show that the median seeing is 3.46 arcsec during the day and 1.80 arcsec during the night. The best nighttime seeing occurs in summer (1.66 arcsec), while the worst occurs in autumn (1.96 arcsec). Seeing exhibits obvious diurnal behavior, with the worst seeing occurring around midday (11:00 to 14:00, Beijing time), and the best seeing just before sunset (18:00 to 20:00, Beijing time). Moreover, the Delingha site has good meteorological properties for astronomical observations during the measurement period, especially the low median wind speed (2.8 m s⁻¹) and great temperature inversion (day: -0.3 K, night: 0.6 K). As for the vertical distribution of |$C_{n}^{2}$|⁠, the exponential h^−0.46 dependency of |$C_{n}^{2}$| varying with height in the GL is also obtained, and its power index is significantly related to the seasons. Furthermore, we calculated the contribution of optical turbulence in the GL to the whole atmosphere. Turbulence within the GL contributes significantly in summer, and its contribution can reach more than 35 %. Finally, we firstly present the complete dependence analysis of seeing on meteorological parameters at the Delingha site. The results show that the best seeing tends to occur when the temperature inversion is sufficiently large, but the dependence of seeing on wind speed is not significant.

Understanding optical turbulence within the atmospheric boundary layer (ABL) is essential for refining atmospheric motion analyses, enhancing numerical weather prediction models, and improving light propagation assessments. This study develops an optical turbulence model for the boundary layer over the South China Sea (SCS) by integrating multiple observational and reanalysis datasets, including ERA5 data from the European Center for Medium-Range Weather Forecasts (ECMWF), radiosonde observations, coherent Doppler wind lidar (CDWL), and ultrasonic anemometer (CSAT3) measurements. Utilizing Monin–Obukhov Similarity Theory (MOST) as the theoretical foundation, the model’s performance is evaluated by comparing its outputs with the observed diurnal cycle of near-surface optical turbulence. Error analysis indicates a root mean square error (RMSE) of less than 1 and a correlation coefficient exceeding 0.6, validating the model’s predictive capability. Moreover, this study demonstrates the feasibility of employing ERA5-derived temperature and pressure profiles as alternative inputs for optical turbulence modeling while leveraging CDWL’s high-resolution observational capacity for all-weather turbulence characterization. A comprehensive statistical analysis of the atmospheric refractive index structure constant ($C_n^2$) from November 2019 to September 2020 highlights its critical implications for optoelectronic system optimization and astronomical observatory site selection in the SCS region.

In this study, we devised a constraint method, called multi-model ensemble pattern (MEP), to estimate the refractive index structure parameter ($C_n^2$) profiles based on observational data and multiple existing models. We verified this approach against radiosonde data from field campaigns in China’s eastern and northern coastal areas. Multi-dimensional statistical evaluations for the $C_n^2$ profiles and integrated astronomical parameters have proved MEP’s relatively reliable performance in estimating optical turbulence in the atmosphere. The correlation coefficients of MEP and measurement overall $C_n^2$ in two areas are up to 0.65 and 0.76. A much higher correlation can be found for a single radiosonde profile. Meanwhile, the difference evaluation of integrated astronomical parameters also shows its relatively robust performance compared to a single model. The prowess of this reliable approach allows us to carry out regional investigation on optical turbulence features with routine meteorological data soon.

We verified the feasibility of an alternative solution to generate temperature and pressure profiles with the U.S. standard atmosphere model (USSA-76). We simultaneously integrated this model with conventional meteorological parameters measured by a weather station in the course of estimating the refractive index structure constant ( C n 2 ). Moreover, a continuous-time-series estimation method of the refractive index structure constant was established within the marine atmospheric boundary layer (ABL) based on wind data obtained from a coherent Doppler wind lidar (CDWL). We also analyzed the optical turbulence characteristics induced by wind shear during the conducted experiment. Laminated and patchy stratified turbulences, which affect the performance of imaging and light transmission systems, were found within the marine ABL. Additionally, the relationship between the ABL and all atmospheric optical turbulence factors shows that the ratio of marine ABL in the entire layer differs from that reported in previous studies. Moreover, the influence of thermal turbulence factors within the marine ABL was less than that of the entire layer in our case. We report a real-time C n 2 estimation method based on a CDWL. The characteristics of the marine ABL C n 2 constitute a reference for optoelectronic applications.

Long-term variations in precipitable water vapor (PWV) and temperature are critical for ground-based astronomical observations at infrared, millimeter, and sub-millimeter wavelengths. This study presents a comprehensive 40 yr analysis (1984–2023) of atmospheric conditions at the Delingha Observatory on the northeastern Tibetan Plateau, based on ERA5 reanalysis and in situ measurements. The site exhibits a median PWV of 3.96 mm, with PWV remaining below 6.00 mm for approximately 63% of the time. The median temperature is 2.32°C, with a median nighttime variation amplitude of 11.97°C. Both PWV and temperature exhibit strong seasonal cycles, with highest values typically observed in summer (peaking in July) and lowest in winter (January). Statistically significant long-term trends are observed, with annual mean PWV increasing by +0.24 mm decade⁻¹ and temperature rising by +0.42°C decade⁻¹. Furthermore, the observed correlations suggest that PWV is significantly modulated by the North Atlantic Oscillation (NAO) and the Pacific Decadal Oscillation (PDO), while temperature also shows significant correlations with the El Niño-outhern Oscillation, in addition to the NAO and PDO, with phase lags ranging from 0 to 11 months. These findings highlight the importance of incorporating climate diagnostics into long-term planning for telescope scheduling and site management.