Study of the Cn2 Model through the New Dimensionless Temperature Structure Function near the Sea Surface in the South China Sea

The refractive index structure constant C-n(2) near the ocean surface is an important parameter for studying atmospheric optical turbulence over the ocean. The measured refractive index structure constant and meteorological parameters, such as temperature and three-dimensional wind speed, near the sea surface on the South China Sea during the period from January to November 2020 were analyzed. On the basis of Monin-Obukhov similarity theory, the dimensionless temperature structure parameter function f(T) near the sea surface was established, and a new parameterized model of the near-sea surface was proposed. The new model improved the error of the widely used model proposed by Wyngaard in 1973 (W73) and better reproduced the daily variation in the measured C-n(2). Further analysis of the seasonal applicability of the new model indicated that the correlation coefficients between the estimated and measured C-n(2) in the spring, summer, autumn, and winter were 0.94, 0.94, 0.95, and 0.89, respectively, and the root mean square errors were 0.32, 0.41, 0.46, and 0.40 m(-2/3), respectively. Compared with the C-n(2) estimated by the W73 model, the correlation coefficient of C-n(2) estimated by the new model and measured by the micro-thermometer increased by 0.05-0.27 and the root mean square error decreased by 0.04-0.56. The improved f(T) demonstrated higher accuracy than the existing models, which can lay a foundation for estimating turbulence parameters in different sea areas.