Publications
2008
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(2008) Physical review letters. 101, 19, 194504. Abstract
We present experimental results on turbulence generated in thin fluid layers in the presence of a large-scale coherent flow, or a spectral condensate. It is shown that the condensate modifies the third-order velocity moment in a much wider interval of scales than the second one. The modification may include the change of sign of the third moment in the inverse cascade. This observation may help resolve a controversy on the energy flux in mesoscale atmospheric turbulence (10-500 km): to recover a correct energy flux from the third velocity moment one needs first to subtract the coherent flow. We find that the condensate also increases the velocity flatness.
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(2008) Journal Of Statistical Mechanics-Theory And Experiment. 2008, 8, P08005. Abstract
We discuss fluctuation relations in simple cases of non-equilibrium Langevin dynamics. In particular, we show that, close to non-equilibrium steady states with non-vanishing probability currents, some of these relations reduce to a modified version of the fluctuation-dissipation theorem. The latter may be interpreted as the equilibrium-like relation in the reference frame moving with the mean local velocity determined by the probability current.
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(2008) Abstract
This is a short course on developed turbulence, weak and strong. The main emphasis is on fundamental properties like universality and symmetries. Two main notions are explained: i) fluxes of dynamical integrals of motion, ii) statistical integrals of motion.
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(2008) New Journal of Physics. 10, 075019. Abstract
We present a mean-field model of cloud evolution that describes droplet growth due to condensation and collisions and droplet loss due to fallout. The model accounts for the effects of cloud turbulence both in a large-scale turbulent mixing and in a microphysical enhancement of condensation and collisions. The model allows for an effective numerical simulation by a scheme that is conservative in water mass and keeps accurate count of the number of droplets. We first study the homogeneous situation and determine how the rain-initiation time depends on the concentration of cloud condensation nuclei (CCN) and turbulence level. We then consider clouds with an inhomogeneous concentration of CCN and evaluate how the rain initiation time and the effective optical depth vary in space and time. We argue that over-seeding even a part of a cloud by small hygroscopic nuclei, one can substantially delay the onset and increase the amount of precipitation.
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What drives mesoscale atmospheric turbulence?(2008) arXiv. 0805.0390. Abstract
Measurements of atmospheric winds in the mesoscale range (10-500 km) reveal remarkably universal spectra with the $k^{-5/3}$ power law. Despite initial expectations of the inverse energy cascade, as in two-dimensional (2D) turbulence, measurements of the third velocity moment in atmosphere, suggested a direct energy cascade. Here we propose a possible solution to this controversy by accounting for the presence of a large-scale coherent flow, or a spectral condensate. We present new experimental laboratory data and show that the presence of a large-scale shear flow modifies the third-order velocity moment in spectrally condensed 2D turbulence, making it, in some conditions, similar to that observed in the atmosphere.
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(2008) New Journal of Physics. 10, 075012. Abstract
Cloud physics has for a long time been an important segment of atmospheric science. It is common knowledge that clouds are crucial for our understanding of weather and climate. Clouds are also interesting by themselves (not to mention that they are beautiful). Complexity is hidden behind the common picture of these beautiful and interesting objects. The typical school textbook definition that a cloud is 'a set of droplets or particles suspended in the atmosphere' is not adequate. Clouds are complicated phenomena in which dynamics, turbulence, microphysics, thermodynamics and radiative transfer interact on a wide range of scales, from sub-micron to kilometres. Some of these interactions are subtle and others are more straightforward. Large and small-scale motions lead to activation of cloud condensation nuclei, condensational growth and collisions; small changes in composition and concentration of atmospheric aerosol lead to significant differences in radiative properties of the clouds and influence rainfall formation. It is justified to look at a cloud as a composite, nonlinear system which involves many interactions and feedback. This system is actively linked into a web of atmospheric, oceanic and even cosmic interactions.
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(2008) IUTAM SYMPOSIUM ON HAMILTONIAN DYNAMICS, VORTEX STRUCTURES, TURBULENCE. Borisov AV., Mamaev IS., Sokolovskiy MA. & Kozlov VV.(eds.). Vol. 6. p. 257-267 (trueIUTAM Bookseries). Abstract
We describe a new effect of floaters clustering by surface waves. This clustering is a result of the surface tension force, which for small particles becomes comparable with their weight. Surface tension creates a difference between the masses of a particle and displaced liquid making the particle effectively inertial. Inertia, positive for hydrophobic or negative for hydrophilic particles, causes particle clustering in the nodes or antinodes of a standing wave and leads to chaotic mixing in random waves. Here we show experimentally that in a standing wave the clustering rate is proportional to the squared wave amplitude. In the case of random waves we demonstrate that inertia effects change statistics of floater distribution and particles concentrate on a multifractal set.
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(2008) Cambridge: . Vol. 355. (trueLondon Mathematical Society lecture note series). Abstract
Methods of non-equilibrium statistical mechanics play an increasingly important role in modern turbulence research, yet the range of relevant tools and methods is so wide and developing so fast that until now there has not been a single book covering the subject. As an introduction to modern methods of statistical mechanics in turbulence, this volume rectifies that situation. The book comprises three harmonised lecture courses by world class experts in statistical physics and turbulence: John Cardy introduces Field Theory and Non-Equilibrium Statistical Mechanics; Gregory Falkovich discusses Turbulence Theory as part of Statistical Physics; and Krzysztof Gawedzki examines Soluble Models of Turbulent Transport. To encourage readers to deepen their understanding of the theoretical material, each chapter contains exercises with solutions. Essential reading for students and researchers in the field of theoretical turbulence, this volume will also interest any scientist or engineer who applies knowledge of turbulence and non-equilibrium physics to their work.
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