Intercomparison of flux-, gradient-, and variance-based optical turbulence (𝐶2𝑛 ) parameterizations

For free-space optical communication or ground-based optical astronomy, ample data of optical turbulence strength (𝐶2𝑛) are imperative but typically scarce. Turbulence conditions are strongly site dependent, so their accurate quantification requires in situ measurements or numerical weather simulations. If 𝐶2𝑛 is not measured directly (e.g., with a scintillometer), 𝐶2𝑛 parameterizations must be utilized to estimate it from meteorological observations or model output. Even though various parameterizations exist in the literature, their relative performance is unknown. We fill this knowledge gap by performing a systematic three-way comparison of a flux-, gradient-, and variance-based parameterization. Each parameterization is applied to both observed and simulated meteorological variables, and the resulting 𝐶2𝑛 estimates are compared against observed 𝐶2𝑛 from two scintillometers. The variance-based parameterization yields the overall best performance, and unlike other approaches, its application is not limited to the lowest part of the atmospheric boundary layer (i.e. the surface layer). We also show that 𝐶2𝑛 estimated from the output of the Weather Research and Forecasting model aligns well with observations, highlighting the value of mesoscale models for optical turbulence modeling.