Non-Kolmogorov atmospheric turbulence and optical signal propagation

International audienceIn the present review, we make an attempt to attract attention to the effect of non-Kolmogorov behavior of turbulence in various scales on the characteristics of electromagnetic waves propagation through a turbulent atmosphere on the example of certain atmospheric experiments. We discuss the interpretation of experimental data based on the model of spectral behavior of a passive scalar field within a broad range of scales, which has been developed recently

Non-Kolmogorov atmospheric turbulence and optical signal propagation

International audience(CJCE 4 oct. 2007, aff. C-429/05, Franfinance, D. 2008. Jur. 458, note H. Claret ; JCP E 2008. 1114, note M. Ho-Dac

Role of phase synchronisation in turbulence

The role of the phase dynamics in turbulence is investigated. As a demonstration of the importance of the phase dynamics, a simplified system is used, namely the one-dimensional Burgers equation, which is evolved numerically. The system is forced via a known external force, with two components that are added into the evolution equations of the amplitudes and the phase of the Fourier modes, separately. In this way, we are able to control the impact of the force on the dynamics of the phases. In the absence of the direct forcing in the phase equation, it is observed that the phases are not stochastic as assumed in the Random Phase Approximation (RPA) models, and in contrast, the non-linear couplings result in intermittent locking of the phases to ± π/2. The impact of the force, applied purely on the phases, is to increase the occurrence of the phase locking events in which the phases of the modes in a wide k range are now locked to ± π/2, leading to a change in the dynamics of both phases and amplitudes, with a significant localization of the real space flow structures

Free and layer turbulent percolation: topological instabilities and their suppression

It is shown (theoretically and experimentally) that topological instabilities lead to free percolation of passive scalar in quasi two-dimensional turbulence that is characterized by the these-dimensional value of the critical exponent $\nu = 0.9$ and by spectral exponent “$-4/3$". Suppression of these instabilities transforms the percolation to layer-type process with $\nu = 4/3$ and spectral exponent “-7/3". In the last case fractal dimension of the passive scalar cluster equals 9/4 and fractal dimension of its perimeter equals 7/4 (i.e. is the same as fractal dimension of the hull of strictly two-dimensional percolation cluster). A good correspondence is found between the spectral and the fractal scaling laws and the atmospheric, numerical and laboratory experimental data