Analysis of Optical Turbulence over the South China Sea Using Balloon-Borne Microthermal Data and ERA5 Data

Abstract

It is very useful for adaptive optics (AO) systems to have appropriate knowledge of optical turbulence. However, due to the limitations of space and time, it is difficult to obtain turbulence parameters, especially in the far sea area. In this paper, the characteristics of optical turbulence over the South China Sea are obtained by analyzing the meteorological data obtained from the field experiment of ocean optical parameters and the fifth set of reanalysis data of the European Centre for Medium-Range Weather Forecasts (ECMWF) for 10 years (2011–2020). Firstly, a new statistical model is proposed based on the measured data and the Hufnagel-Valley 5/7, which can well reconstruct the atmospheric turbulence characteristics of the South China Sea. Secondly, according to the comparison between the temperature and wind speed data in ERA5 data and microthermal measurement, the ERA5 data have good reliability, with the temperature deviation basically less than 1.5 K and the wind speed deviation basically less than 2 m∙s−1. Thirdly, the vertical distributions and seasonal behavior of the turbulence strength at the determined location are analyzed, which shows that the turbulence strength in the upper atmosphere is strongest in summer, followed by autumn and winter, and weakest in spring. Then, the distribution profile of the Richardson number provides us with the relative probability of the existence of optical turbulence. During summer and September, the instability of the atmosphere is significantly larger than other months and the extremely low intensity in April indicates the most stable condition in all months. Finally, the analysis results of turbulence parameter profiles for many years show that there is good consistency between different parameters.