Optical seeing—mechanism of formation of thin turbulent laminae in the atmosphere

Abstract

Data from balloon soundings taken at sites in the Canary Islands, France, and Chile are used to show that hydrodynamic instability, perhaps engendered by the propagation of buoyancy (gravity) or other waves, leads to the formation of thin, turbulent laminae, or "seeing layers." These seeing layers occur almost invariably in pairs and exhibit large values for the temperature-structure coefficient C(T)(2) because they form where the gradient of temperature is particularly steep. The refractive-index-structure coefficient is correspondingly large, and so these layers adversely affect the quality of optical propagation. The mechanism proposed here is already known to create clear air turbulence in the stratosphere, and we show how it is consistent with the formation of thin turbulent seeing layers in the troposphere and the stratosphere at night, when the atmosphere is generally stably stratified.

Atmospheric turbulence and wind profiles monitoring with generalized scidar

“…The GS velocity values seem to be concentrated in zones where the balloon data show strong vertical gradients of the wind velocity (either in its modulus or its direction, shown in Figs. 3 and 4, respectively), which agrees with the scenario in which the velocity gradient breaks the stratification, generating dynamical turbulence, which in turn, in the presence of a potential temperature gradient, generates optical turbulence (Coulman et al 1995;Werne & Fritts 1999, and references therein).…”

First evidence of the finite horizontal extent of the optical turbulence layers. Implications for new adaptive optics techniques

“…5). The C 2 N depends directly on the gradient of the temperature and the wind velocity (Coulman et al 1995) so we deduce that the meteorological parameters and probably the optical turbulence during this night were relatively uniform above 10 km. This is consistent with a good correlation between the simulated C 2 N and that measured by the balloon.…”

3D numerical simulations of optical turbulence at the Roque de Los Muchachos Observatory using the atmospherical model Meso-Nh

“…The principal difficulty is the identification of the turbulence sources. The most reliable hypothesis (Coulman et al 1995) is that small wind instabilities could create a dynamic turbulence that mixes air particles with different temperatures in such a way as to reduce the temperature gradient in an extended region of some ten kilometers bounded in the upper and lower side by thin stable shears. In the energy budget considered in the precedent feasibility study we always omitted the contribution of the radiation transfer.…”