Another Look at the Refractive Index Structure Function

This paper discusses the derivation of the refractive index structure function. It shows that the traditional formulation, which is based on the hydrostatic assumption, leads to increasing errors with height when compared with a formulation that is based on the potential temperature. The paper corrects a long-standing problem of extrapolating the traditional boundary layer approximation beyond its region of validity (i.e., to the upper troposphere and lower stratosphere). The new derivation may have applications in observational work to measure C-n(2) and seeing and in numerical modeling efforts. A preliminary analysis of the influence of the new formulation in numerical modeling of seeing suggests that impact on seeing will be small in general, because the largest contribution to seeing generally comes from the lower troposphere. However, an accurate C-n(2) profile is needed because other astroclimatic parameters, such as the isoplanatic angle, can suffer from the lack of C-n(2) accuracy at high altitude. This work may also have application in radar meteorology, since clear-air radar sensitivity depends on accurate estimation of C-n(2).