Comparing Different Methodologies of Quantifying Surface Layer Turbulence

Temperature and moisture gradients within the boundary layer cause optical turbulence and can be quantified using the refractive index structure parameter (C_n²), which describes changes in the refractive index of the air over a distance and can be derived from the temperature structure parameter, C_T². This parameter relies largely on the sensible heat flux in the surface layer. C_n² can be quantified with the use of sonic anemometers by accounting for fluctuations in sonic temperature at one height above the surface. An Eddy Covariance System also quantifies turbulence by measuring changes in H₂O and CO₂ concentrations in one layer of the atmosphere. Often the sensible heat flux is calculated using the Bulk Aerodynamic Method which makes assumptions about the surface roughness, the change in wind speed with height (friction velocity) and is also dependent on atmospheric stability thus requiring various stability corrections. A method that does not require as many assumptions is the Energy Balance Bowen Ratio method of quantifying sensible heat. The Bowen Ratio is the ratio of sensible heat flux to latent heat flux and is derived using readily available meteorological data such as temperature, pressure, humidity, plus net radiation, and ground heat flux—and no reliance on highly variable surface layer wind or stability characterizations. The purpose of this research is to compare these four methods of quantifying C_n² to determine the most practical and accurate method of quantifying surface layer optical turbulence, a parameter that is not currently well characterized in numerical weather prediction models.