关键词: 大气光学, 湍流, 大气边界层, 折射率结构常数, 耗散率

Abstract: Objective　Turbulent transport is a crucial process for the transmission of substances and energy within the atmospheric medium. Currently research on atmospheric optical turbulence predominantly focuses on inland regions, with relatively less studies dedicated to the optical properties of marine atmospheres. China is a coastal nation with over 3 million square kilometers of maritime territory. The ocean has a high specific heat capacity and exhibits characteristics of local circulation, so its atmospheric properties are completely different from those of the inland atmosphere. Conducting basic research on the characteristics of marine atmospheric optical turbulence is helpful to effectively mitigate the impact or interference of atmospheric optical turbulence on photoelectronic systems, and has theoretical significance and practical value for research on pollutant transport, weather changes, and forecasting in coastal areas. Methods　This paper primarily uses coherent Doppler lidar to detect turbulent parameters such as the characteristics of sea, land and atmospheric wind fields, turbulent energy dissipation rate ε and refractive index structure constant C2 n . The equipment has the advantages of high spatiotemporal resolution and continuous real-time observation. Specifically, wind measurement data from coherent Doppler lidar are combined with ground-based meteorological stations data and standard atmospheric model to establish an outer-scale parameterization model L0, which is used to retrieve C2 n . Subsequently, ε was calculated using the velocity structure function DV (r), together with L0 and the standard deviation of vertical velocity σa within the boundary layer. Furthermore, the spatiotemporal variation characteristics of C2 n and ε were studied, and the correlations of C2 n with ε and the vertical velocity variance σ 2 a were analyzed. Results and Discussion　The coherent Doppler lidar data from April 3rd and 9th in 2020 were utilized to analyze the estimation results near the coast, when the atmospheric weather conditions were favorable during the daytime, and the realtime meteorological station data were combined with the temperature and pressure model to calculate temperature and pressure profiles. After calculating the refractive index gradient, an external scale model was used to estimate the C2 n profile, and its diurnal variation with height and spatiotemporal characteristics were analyzed. The results showed that the intensity of turbulence near the ground is usually the strongest and gradually decreases with the increasing height. At a height of 100 meters, there is a significant diurnal variation. During the daytime, the turbulence intensity is generally higher than that at night. And as the altitude increases, this diurnal pattern gradually diminishes. This phenomenon indicates that the spatiotemporal variation of atmospheric turbulence intensity is complex. The lidar data from April 3rd and 9th were also used to analyze the estimation results for ε , with a focus on its spatiotemporal characteristics. The magnitude of ε ranged from 10−6 and 10−1 m2/s3, primarily clustered within 10−4 to 10−2 m2/s3. The diurnal variation of ε was relatively complex. Below the boundary layer, it generally decreased with increasing altitude. the correlations of C2 n with σ 2 a and ε were analyzed. During the daytime, C2 n showed a relatively high correlation with ε, reaching above 0.89, and the correlation between C2 n and σ 2 a could reach above 0.57. The favorable correlation between C2 n and σ 2 a indicates that the turbulent motion is locally isotropic, which means that the statistical characteristics of turbulence do not change with the variation of the spatial direction. Conclusions　In this study, coherent Doppler lidar was used to detect the characteristics of atmospheric wind field at a specific observation site in the South China Sea region. By combining standard atmospheric models and outer scale models, the spatiotemporal characteristics of C2 n and ε in this region were analyzed, and the correlations of C2 n with ε and σ 2 a were also investigated. It is shown that the atmospheric turbulence in the coastal region is highly complex. Below the boundary layer, it gradually decreases as the height increases. The magnitude of ε is mainly between 10−4 and 10−2 m2/s3. Correlation analysis indicates that under conditions of fully developed turbulence, the correlation between C2 n and ε is relatively high, with a correlation coefficient above 0.8. The correlation between C2 n and σ 2 a can reach above 0.5. The favorable correlation estimated between C2 n and σ 2 a indicates isotropic turbulence characteristics in this region. This paper not only verifies the feasibility of using coherent Doppler lidar data to estimate the boundary layer turbulence parameters in coastal areas, but also reasonably validates the relevant algorithms used in the research. However, due to the observation location being located in the coastal area with relatively complex atmospheric conditions the interaction between sea and land has a significant impact, such as the transport and diffusion of water vapor by sea-land winds and sudden changes in local climate. Therefore, in-depth analysis and research of turbulence parameter variations in the coastal area still require further comparative analyses with continuous synchronous detection data from various other observation devices.

Key words: atmospheric optics, turbulence, atmospheric boundary layer, refractive index structure constant, dissipation rate 548