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

Abstract

The refractivity structure constant C n 2 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. C n 2 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, C n 2 varied predominantly between 10 - 14 and 10 - 13 m - 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) L 0 v and L 0 h , in vertical and horizontal directions respectively, has offered opportunities for the determination of the Ozmidov scale L R (proportional to Tatarskii's L 0 ) as well as the overturning turbulent length scale L t . 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 L R is approximately one order of magnitude larger than L t and the latter is again one order of magnitude larger than L 0 v . During strongly stratified situations L R ≈ L t ≳ L 0 v which is in good agreement with other results from in situ and laboratory measurements. Finally, we empirically found that the turbulence anisotropy L 0 h / L 0 v is roughly proportional to the Richardson number with a proportionality factor of 30.