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

Abstract

The refractive index structure constant Cn2 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 fT 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 Cn2. Further analysis of the seasonal applicability of the new model indicated that the correlation coefficients between the estimated and measured Cn2 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 Cn2 estimated by the W73 model, the correlation coefficient of Cn2 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 fT demonstrated higher accuracy than the existing models, which can lay a foundation for estimating turbulence parameters in different sea areas.