The Experts below are selected from a list of 373752 Experts worldwide ranked by ideXlab platform
Y Liu - One of the best experts on this subject based on the ideXlab platform.
-
coherent modes and Turbulences observations with multi channel doppler reflectometer on experimental advanced superconducting tokamak
Physics of Plasmas, 2020Co-Authors: Xuefei Feng, A D Liu, C Zhou, X L Zou, G Zhuang, T B Wang, Y Liu, S X Wang, T H Shi, Mengyu WangAbstract:With a newly installed 5-channel W-band Doppler reflectometer (DR) in EAST tokamak, many interesting coherence modes and Turbulences have been observed. In this paper, the tearing mode (TM), a novel inter-edge localized mode (ELM) electromagnetic mode, and the eigenmode geodesic acoustic mode (GAM) accompanied by a broadband quasi-coherent mode (QCM) during H-mode stage have been reported. The TM could be directly observed in both density fluctuation and perpendicular velocity fluctuation at the DR channel localized in the magnetic island region; moreover, many high-order TM frequency harmonics, dual Turbulence peaks inside and outside the island separatrix, and strong flow shear across the island separatrix could also be observed. A high-frequency ( ∼ 230 kHz) electromagnetic mode (toroidal mode number n = 1) could be identified. The mode is generated dozens of milliseconds before the ELM crash and may affect the ELM dynamic process. The eigenmode GAM excited during the H-mode stage is generated near the top of the density pedestal and then propagates radially inward with a radial wavenumber of about 1 cm − 1. A broadband QCM with a frequency range of 20 – 100 kHz is always accompanied by eigenmode GAM and nonlinearly coupled with both GAM and the background Turbulence from the bispectrum analysis. All these results convince the validity of the Doppler reflectometer in multi-scale measurement from the mesoscale to microscale.
-
properties and selected implications of magnetic Turbulence for interstellar medium local bubble and solar wind
Space Science Reviews, 2009Co-Authors: Alex Lazarian, Andrey Beresnyak, Huirong Yan, M Opher, Y LiuAbstract:Astrophysical fluids, including interstellar and interplanetary medium, are magnetized and turbulent. Their appearance, evolution, and overall properties are determined by the magnetic Turbulence that stirs it. We argue that examining magnetic Turbulence at a fundamental level is vital to understanding many processes. A point that frequently escapes the attention of researchers is that magnetic Turbulence cannot be confidently understood only using “brute force” numerical approaches. In this review we illustrate this point on a number of examples, including intermittent heating of plasma by Turbulence, interactions of Turbulence with cosmic rays and effects of Turbulence on the rate of magnetic reconnection. We show that the properties of magnetic Turbulence may vary considerably in various environments, e.g. imbalanced (or cross-helical) Turbulence in solar wind differs from balanced Turbulence and both of these differ from Turbulence in partially ionized gas. Appealing for the necessity of more observational data on magnetic fields, we discuss a possibility of studying interplanetary Turbulence using alignment of Sodium atoms in the tail of comets.
-
properties and selected implications of magnetic Turbulence for interstellar medium local bubble and solar wind
arXiv: Astrophysics, 2008Co-Authors: Alex Lazarian, Andrey Beresnyak, Huirong Yan, M Opher, Y LiuAbstract:Astrophysical fluids, including interstellar and interplanetary medium, are magnetized and turbulent. Their appearance, evolution, and overall properties are determined by the magnetic Turbulence that stirs it. We argue that examining magnetic Turbulence at a fundamental level is vital to understanding many processes. A point that frequently escapes the attention of researchers is that magnetic Turbulence cannot be confidently understood only using "brute force" numerical approaches. In this review we illustrate this point on a number of examples, including intermittent heating of plasma by Turbulence, interactions of Turbulence with cosmic rays and effects of Turbulence on the rate of magnetic reconnection. We show that the properties of magnetic Turbulence may vary considerably in various environments, e.g. imbalanced Turbulence in solar wind differs from balanced Turbulence and both of these differ from Turbulence in partially ionized gas. Appealing for the necessity of more observational data on magnetic fields, we discuss a possibility of studying interplanetary Turbulence using alignment of Sodium atoms in the tail of comets.
Jielun Sun - One of the best experts on this subject based on the ideXlab platform.
-
review of wave Turbulence interactions in the stable atmospheric boundary layer
Reviews of Geophysics, 2015Co-Authors: Jielun Sun, L Mahrt, Carmen J Nappo, Danijel Belusic, Branko Grisogono, David R Stauffer, Manuel Pulido, Chantal Staquet, Qingfang Jiang, A PouquetAbstract:Flow in a stably stratified environment is characterized by anisotropic and intermittent Turbulence and wavelike motions of varying amplitudes and periods. Understanding Turbulence intermittency and wave-Turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. The stable atmospheric boundary layer (SABL) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. Intermittent Turbulence intensification in the SABL impacts human activities and weather variability, yet it cannot be generated in state-of-the-art numerical forecast models. This failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random Turbulence generation in a stably stratified flow, in which wave-Turbulence interaction is a potential mechanism for Turbulence intermittency. A workshop on wave-Turbulence interactions in the SABL addressed the current understanding and challenges of wave-Turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent Turbulence from the perspectives of theory, observations, and numerical parameterization. There have been a number of reviews on waves, and a few on Turbulence in stably stratified flows, but not much on wave-Turbulence interactions. This review focuses on the nocturnal SABL; however, the discussions here on intermittent Turbulence and wave-Turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general.
-
Turbulence regimes and Turbulence intermittency in the stable boundary layer during cases 99
Journal of the Atmospheric Sciences, 2012Co-Authors: Jielun Sun, L Mahrt, Robert M Banta, Yelena L PichuginaAbstract:AbstractAn investigation of nocturnal intermittent Turbulence during the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99) revealed three Turbulence regimes at each observation height: 1) regime 1, a weak Turbulence regime when the wind speed is less than a threshold value; 2) regime 2, a strong Turbulence regime when the wind speed exceeds the threshold value; and 3) regime 3, a moderate Turbulence regime when top-down Turbulence sporadically bursts into the otherwise weak Turbulence regime. For regime 1, the strength of small Turbulence eddies is correlated with local shear and weakly related to local stratification. For regime 2, the Turbulence strength increases systematically with wind speed as a result of Turbulence generation by the bulk shear, which scales with the observation height. The threshold wind speed marks the transition above which the boundary layer approaches near-neutral conditions, where the turbulent mixing substantially reduces the stratification and temperature fluc...
Ian P Castro - One of the best experts on this subject based on the ideXlab platform.
-
a turbulent patch arising from a breaking internal wave
Journal of Fluid Mechanics, 2011Co-Authors: Sergey N Yakovenko, Glyn T Thomas, Ian P CastroAbstract:Results of direct numerical simulations of the development of a breaking internal gravity wave are presented. The wave was forced by the imposition of an appropriate bottom boundary shape (a two-dimensional cosine hill) within a density-stratified domain having a uniform upstream velocity and density gradient. The focus is on Turbulence generation and maintenance within the turbulent patch generated by the wave breaking. Pathlines, density contours, temporal and spatiral spectra, and second moments of the velocity and density fluctuations and turbulent kinetic energy balance terms obtained from the data averaged over the span in the mixed zone are all used in the analysis of the flow. Typical Reynolds numbers, based on the vertical scale of the breaking region and the upstream velocity, were around 6000 and the fully resolved computations yielded sufficient resolution to capture the fine-scale transition processes as well as the subsequent fully developed turbilence. It is shown that globally, within the turbulent patch, there is an approximate balance in the production, dissipation and transport processes for turbulent kinetic energy, so that the patch remains quasi-steady over a significant time. Although it is far from being axially homogenous, with Turbulence generation occurring largely near the upstream bottom part of the patch where the mean velocity shear is particularly large, it has features not dissimilar to those of a classical turbulent wake
Robert W Boyd - One of the best experts on this subject based on the ideXlab platform.
-
influence of atmospheric Turbulence on states of light carrying orbital angular momentum
Optics Letters, 2012Co-Authors: Brandon Rodenburg, Martin P J Lavery, Mehul Malik, Malcolm N Osullivan, Mohammad Mirhosseini, David Robertson, Miles J Padgett, Robert W BoydAbstract:We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric Turbulence. The Turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov Turbulence theory. We introduce this simulated Turbulence through the use of a phase-only spatial light modulator. Once the Turbulence is introduced, the degradation in mode quality results in crosstalk between OAM modes. We study this crosstalk in OAM for 11 modes, showing that Turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number.
-
influence of atmospheric Turbulence on states of light carrying orbital angular momentum
arXiv: Optics, 2012Co-Authors: Brandon Rodenburg, Martin P J Lavery, Mehul Malik, Malcolm N Osullivan, Mohammad Mirhosseini, Miles J Padgett, David J Robertson, Robert W BoydAbstract:We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric Turbulence. The Turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov Turbulence theory. We introduce this simulated Turbulence through the use of a phase-only spatial light modulator. Once the Turbulence is introduced, the degradation in mode quality results in cross-talk between OAM modes. We study this cross-talk in OAM for eleven modes, showing that Turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number.
L Mahrt - One of the best experts on this subject based on the ideXlab platform.
-
review of wave Turbulence interactions in the stable atmospheric boundary layer
Reviews of Geophysics, 2015Co-Authors: Jielun Sun, L Mahrt, Carmen J Nappo, Danijel Belusic, Branko Grisogono, David R Stauffer, Manuel Pulido, Chantal Staquet, Qingfang Jiang, A PouquetAbstract:Flow in a stably stratified environment is characterized by anisotropic and intermittent Turbulence and wavelike motions of varying amplitudes and periods. Understanding Turbulence intermittency and wave-Turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. The stable atmospheric boundary layer (SABL) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. Intermittent Turbulence intensification in the SABL impacts human activities and weather variability, yet it cannot be generated in state-of-the-art numerical forecast models. This failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random Turbulence generation in a stably stratified flow, in which wave-Turbulence interaction is a potential mechanism for Turbulence intermittency. A workshop on wave-Turbulence interactions in the SABL addressed the current understanding and challenges of wave-Turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent Turbulence from the perspectives of theory, observations, and numerical parameterization. There have been a number of reviews on waves, and a few on Turbulence in stably stratified flows, but not much on wave-Turbulence interactions. This review focuses on the nocturnal SABL; however, the discussions here on intermittent Turbulence and wave-Turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general.
-
Turbulence regimes and Turbulence intermittency in the stable boundary layer during cases 99
Journal of the Atmospheric Sciences, 2012Co-Authors: Jielun Sun, L Mahrt, Robert M Banta, Yelena L PichuginaAbstract:AbstractAn investigation of nocturnal intermittent Turbulence during the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99) revealed three Turbulence regimes at each observation height: 1) regime 1, a weak Turbulence regime when the wind speed is less than a threshold value; 2) regime 2, a strong Turbulence regime when the wind speed exceeds the threshold value; and 3) regime 3, a moderate Turbulence regime when top-down Turbulence sporadically bursts into the otherwise weak Turbulence regime. For regime 1, the strength of small Turbulence eddies is correlated with local shear and weakly related to local stratification. For regime 2, the Turbulence strength increases systematically with wind speed as a result of Turbulence generation by the bulk shear, which scales with the observation height. The threshold wind speed marks the transition above which the boundary layer approaches near-neutral conditions, where the turbulent mixing substantially reduces the stratification and temperature fluc...
