| The atmospheric optical turbulence characteristics of the marine boundary layer is an important part of the marine atmospheric research,which is very significant for understanding the interaction between the ocean and the atmosphere,oceanographic forecasting and the role of the ocean in the global climate.Atmospheric turbulence is an irregular random movement phenomenon in the atmosphere.In the application of photoelectric engineering,the turbulent cause a series of phenomena such as beam drift,beam spreading and phase fluctuation,resulting in the decline of beam quality,which seriously restricts the use of optical systems.The characteristic quantity of marine turbulence is affected by ocean and atmosphere,which is the key factor to study the interaction of air-sea and the dynamics of ocean boundary layer.In addition,the ocean stores a large amount of carbon,so the study of marine boundary layer turbulence is also of great significance to describe the law of carbon sink.The refractive index structure constant Cn2 in the marine boundary layer is one of the important parameters for studying the optical turbulence of the atmosphere over the ocean.Restricted by marine observation conditions,it is difficult to obtain maritime data,and the Cn2 data at sea is seriously missing.In order to solve these problems,we estimated the refractive index structure constant Cn2 of the marine atmosphere by using the parameterized similarity function based on the Monin-Obukhov similarity theory and conventional meteorological elements that are relatively easy to observe,and then obtained the distribution characteristics of Cn2 in typical sea areas.The existing similarity function may not be suitable for the estimation of Cn2 over the China Sea and adjacent sea area.After comparing with the experimental results,we proposed a new similarity function fT.Considering the temporal and spatial discontinuities of the observation data,we tried the new way of using the COARE algorithm which is commonly used to estimate the air-sea fluxes,and combing with the reanalysis data with a wide measurement range to estimate Cn2.The main work and results of this paper are as follows:1.The basic content of observation data and reanalysis data was introduced in detail.The observation data mainly include conventional meteorological data and atmospheric refractive index structure constant Cn2 data.Among them,the measuring instruments of Cn2 include a micro-thermometer and a three-dimensional ultrasonic anemometer.The measurement principle,data preprocessing method and detailed steps of the three-dimensional ultrasonic anemometer(CSAT3)were described in detail.Taking the observed data of the Yellow Sea as an example,the relationship between the meteorological data was analyzed,and the daily variationt of turbulence characteristics and the Cn2 revised by virtual temperature correction were analyzed.In this way,the feasibility and effectiveness of the pretreatment process of CSAT3 data were verified,and the cross-verification was done with the Cn2 measured by the micro-thermometer.2.The characteristics of atmospheric optical turbulence near the Yellow Sea and South China Sea were compared and analyzed.Based on the conventional meteorological parameters and the Cn2 observed in two typical sea areas from September 2019 to August 2020 in the Yellow Sea coast and the South China Sea islands,the statistical analysis results show that the two sea areas showed obvious daily variations and seasonal characteristics,the turbulence intensity was higher during the day than at night,and both atmospheric temperature and wind speed were important factors affecting the turbulence intensity.The turbulence intensity in daytime is higher than that at night,and atmospheric temperature and wind speed are both important factors affecting the turbulence intensity.The probability distributing curves of log10(Cn2)were fitted respectively by comparing the differences of parameters between the two seas,and the results showed that log10(Cn2)was highly consistent with normal distribution.The data analysis in this part provided basic data for the study of atmospheric turbulence over the ocean,which has certain reference value for the construction of the marine database,and at the same time lays the foundation for proposing a new Cn2 model.3.A new parameterized Cn2 model in the South China Sea was proposed.The measured refractive index structure constant and meteorological parameters,such as air 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 Cn2 model of the near-sea surface was proposed.Further analysis of the seasonal applicability of the new model shows that the performance of the new function in different seasons is better than that of the existing models,especially the stable conditions.Compared with the existing models,both the correlation and the estimation accuracy have been improved.The proposal of the new function lays a foundation for further study of atmospheric turbulence characteristics in China’s surrounding sea areas,and also provides a new idea for estimating turbulence parameters in other seas.4.A new method for estimating Cn2 in the South China Sea was established by using the COARE algorithm to estimate the turbulence characteristics combined with the new function fT.The CO ARE algorithm is an air-sea interface research algorithm based on bulk parameterized method and similarity theory,which is often used to calculate air-sea heat and turbulent flux.Due to the problems of few observation data,sparse sites and difficult observation,we estimated the turbulent flux and characteristics by using the reanalysis data covering a wide range and spatiotemporal continuity,and calculated Cn2 combined with the proposed new function fT.Compared with the observed Cn2,there were some errors in the estimation results.The accuracy was improved after correction,and the Cn2 spatial distribution over the China Sea and adjacent sea area was obtained. |
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