Refractivity structure constant and length scales from mm-wave propagation in the stably stratified troposphere

The refractivity structure constant Cn2 and length scales of turbulence are measured at mm-wavelengths with line-of-sight propagation experiments at an average height of 200 m above ground at Bern (Switzerland) and El Leoncito (Argentina) in the stably stratified troposphere. Cn2 at mm-wavelengths is of raised importance for scientific and commercial applications, as this frequency band has become easier accessible in recent years. At Bern, Cn2 varied predominantly between 10-14 and 10-13m-2/3, whereas at the astronomical site of El Leoncito, with its desert-like conditions, it was approximately ten times less. Simultaneously measured potential refractivity gradients M and outer scale lengths of turbulence (proportional to integral scale) L0v and L0h, in vertical and horizontal directions respectively, has offered opportunities for the determination of the Ozmidov scale LR (proportional to Tatarskii's L0) as well as the overturning turbulent length scale Lt. This has been hardly done in the past, and probably never so far with spatially averaged length scales using remote measurement techniques. For weak stratification we found that LR is approximately one order of magnitude larger than Lt and the latter is again one order of magnitude larger than L0v. During strongly stratified situations LR≈Lt≳L0v which is in good agreement with other results from in situ and laboratory measurements. Finally, we empirically found that the turbulence anisotropy L0h/L0v is roughly proportional to the Richardson number with a proportionality factor of 30.