ABSTRACT
In Chapter 3, the results of long-term experimental studies of the properties of atmospheric turbulence in the anisotropic boundary layer are stated. The correct assignment of turbulent characteristics of the atmosphere is an important premise for the exact forecast of results of the distribution of optical radiation in the atmosphere.
It is established that the similarity theory of turbulent flows can be extended to any anisotropic boundary layer. With use of semiempirical hypotheses of the turbulence theory, it is theoretically and experimentally shown that any anisotropic boundary layer can be considered to be weakly anisotropic locally in which the weakly anisotropic similarity theory of Monin–Obukhov is applied locally (in some vicinity of each point in the layer). It is established that at the known characteristic scales of temperature and velocity, the anisotropic boundary layer can be replaced with isotropic layer. It gives an opporunity to use the optical models of turbulence developed for the isotropic boundary layer.
Processes of origination and disintegration of the Benard cell in air are experimentally studied. Our data confirm the main scenarios of origination of turbulence (the stochastic scenarios of Landau–Hopf, Ruelle–Takens, Feigenbaum, Pomeau–Manneville). It is established that the disintegration of the Benard cell is realized according to the Feigenbaum's scenario. It is shown that the turbulence appearing due to disintegration is coherent (cophase) and determined. Fractality (local self-similarity) of the turbulence spectrum is illuminated.
The turbulence resulting from the disintegration of the Benard cell meets all the criteria characterizing the appearance of chaos in typical dynamic systems. These signs typically include origination of irregular long-living space structures, the appearance (character) of which is defined by dissipative factors; local instability and fractality of the phase space of such structures; emergence of the central (at the zero frequency) peak in the spectrum. It is convenient to integrate the specified properties under one name “coherent structure,” to expand this already existing concept and to include small-scale components of disintegration of the cell in the composition of coherent structure. We define coherent structure as the compact formation including the long-living space hydrodynamic vortex cell (resulting from long action of thermodynamic gradients) and products of its discrete coherent cascade disintegration.
Our results show that the known processes of transition of laminar flows in turbulent (Rayleigh–Benard convection, the flow fluid around obstacles, etc.) can be considered as coherent structures (or the sums of such structures). It is shown that real atmospheric turbulence can be considered as an incoherent mix of different coherent structures with incommensurable frequencies of the main energy vortices. In the area with the defining influence of one coherent structure (area of coherent turbulence), the value of Kolmogorov and Obukhov constants can significantly differ from the values of Kolmogorov turbulence. In comparison with Kolmogorov turbulence in coherent turbulence, there is a considerable decrease of fluctuations of optical radiation.
