Influence of small‐scale turbulent fluctuations on direct‐path coherence from 4 to 20 kHz

2004 ◽  
Vol 116 (4) ◽  
pp. 2577-2577
Author(s):  
Kevin B. Smith ◽  
Ozer Eroglu
Keyword(s):  
Small Scale ◽  
Direct Path ◽  
Turbulent Fluctuations

scholarly journals Effect of Tidal Stage on Sediment Concentrations and Turbulence by Vessel Wake in a Coastal Plain Saltmarsh

2019 ◽  
Vol 7 (6) ◽  
pp. 192
Author(s):  
Richard Styles ◽  
Michael A. Hartman
Keyword(s):  
Coastal Plain ◽  
Habitat Structure ◽  
Sediment Concentration ◽  
Small Scale ◽  
Characteristic Time Scale ◽  
Suspended Material ◽  
Turbulent Fluctuations ◽  
High Concentrations ◽  
Tidal Stage ◽  
Water Elevation

Vessel generated waves can impact shoreline stability and habitat structure in many waterways. Sheltered regions, such as coastal plain saltmarshes, support fragile ecosystems and can be particularly vulnerable to the effects of unregulated vessel operations. Instruments for measuring currents and sediment concentration were deployed in a coastal plain saltmarsh to examine the small-scale physical characteristics of the vessel wake generated by recreational craft typical of this environment. The response to vessel wake varied sharply depending upon the stage of the tide. At low tide, waves breaking on the exposed bank produced high concentrations of suspended material that were transported offshore through turbulent diffusion. When the water elevation exceeded the toe of the marsh scarp, the concentration and turbulent kinetic energy exhibited less of a statistically significant variation in response to vessel passage. For the most energetic flows, the vessel orbital velocities were dwarfed by turbulent fluctuations generated by the sheared tidal boundary layer. While further research is required, preliminary findings indicate that the dissipation of vessel wake energy may stimulate or enhance shear generated turbulence if the characteristic wave period is similar to the characteristic time scale of the energy containing eddies.

scholarly journals Effects of the Large-Scale Circulation on Temperature and Water Vapor Distributions in the Π Chamber

2021 ◽  
Author(s):  
Jesse C. Anderson ◽  
Subin Thomas ◽  
Prasanth Prabhakaran ◽  
Raymond A. Shaw ◽  
Will Cantrell
Keyword(s):  
Water Vapor ◽  
Large Scale ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Field Measurements ◽  
Skewed Distribution ◽  
Vapor Concentration ◽  
Small Scale ◽  
Large Scale Circulation ◽  
Turbulent Fluctuations

Abstract. Microphysical processes are important for the development of clouds and thus Earth's climate. For example, turbulent fluctuations in the water vapor concentration, r, and temperature, T, cause fluctuations in the saturation ratio, S. Because S is the driving factor in the condensational growth of droplets, fluctuations may broaden the cloud droplet size distribution due to individual droplets experiencing different growth rates. The small scale turbulent fluctuations in the atmosphere that are relevant to cloud droplets are difficult to quantify through field measurements. We investigate these processes in the laboratory, using Michigan Tech's Π Chamber. The Π Chamber utilizes Rayleigh-Benard convection (RBC) to create the turbulent conditions inherent in clouds. In RBC it is common for a large scale circulation (LSC) to form. As a consequence of the LSC, the temperature field of the chamber is not spatially uniform. In this paper, we characterize the LSC in the Π chamber and show how it affects the shape of the distributions of r, T and S. The LSC was found to follow a single roll with an updraft and downdraft along opposing walls of the chamber. Near the updraft (downdraft), the distributions of T and r were positively (negatively) skewed. S consistently had a negatively skewed distribution, with the downdraft being the most negative.

scholarly journals A dynamical model of plasma turbulence in the solar wind

2015 ◽  
Vol 373 (2041) ◽  
pp. 20140145 ◽  
Author(s):  
G. G. Howes
Keyword(s):  
Solar Wind ◽  
Solar Wind Plasma ◽  
Plasma Turbulence ◽  
Alfven Waves ◽  
Dynamical Model ◽  
Alfvén Waves ◽  
Small Scale ◽  
Current Sheets ◽  
Turbulent Fluctuations ◽  
Physical Mechanisms

A dynamical approach, rather than the usual statistical approach, is taken to explore the physical mechanisms underlying the nonlinear transfer of energy, the damping of the turbulent fluctuations, and the development of coherent structures in kinetic plasma turbulence. It is argued that the linear and nonlinear dynamics of Alfvén waves are responsible, at a very fundamental level, for some of the key qualitative features of plasma turbulence that distinguish it from hydrodynamic turbulence, including the anisotropic cascade of energy and the development of current sheets at small scales. The first dynamical model of kinetic turbulence in the weakly collisional solar wind plasma that combines self-consistently the physics of Alfvén waves with the development of small-scale current sheets is presented and its physical implications are discussed. This model leads to a simplified perspective on the nature of turbulence in a weakly collisional plasma: the nonlinear interactions responsible for the turbulent cascade of energy and the formation of current sheets are essentially fluid in nature, while the collisionless damping of the turbulent fluctuations and the energy injection by kinetic instabilities are essentially kinetic in nature.

scholarly journals A nonextensive entropy path to probability distributions in solar wind turbulence

2005 ◽  
Vol 12 (2) ◽  
pp. 171-180 ◽  
Author(s):  
M. P. Leubner ◽  
Z. Vörös
Keyword(s):  
Solar Wind ◽  
Long Range ◽  
Large Scale ◽  
Probability Distributions ◽  
Spatial Separation ◽  
Scale Dependence ◽  
Small Scale ◽  
Time Lags ◽  
Turbulent Fluctuations ◽  
Long Range Interactions

Abstract. The observed scale dependence of the probability distributions of the differences of characteristic solar wind variables is analyzed. Intermittency of the turbulent fluctuations at small-scale spatial separations is accompanied by strongly non-Gaussian distributions that turn into a normal distribution for large-scale separation. Conventional theoretical models are subject to insufficient physical justification since nonlocality in turbulence should be based on long-range interactions, provided recently by the bi-kappa distribution in the context of nonextensive thermo-statistics. Observed WIND and ACE probability distributions are accurately reproduced for different time lags by the one-parameter bi-kappa functional, a core-halo convolution, where kappa measures the degree of nonlocality or nonextensivity in the system. Gradual decoupling is obtained by enhancing the spatial separation scale corresponding to increasing kappa values, where a Gaussian is approached for infinite kappa. Consequently, long-range interactions introduced on the fundamental level of entropy generalization, are able to provide physically the source of the observed scale dependence of the turbulent fluctuations in the intermittent interplanetary medium.

scholarly journals Role of helicity for large- and small-scale turbulent fluctuations

2015 ◽  
Vol 92 (5) ◽  
Author(s):  
Ganapati Sahoo ◽  
Fabio Bonaccorso ◽  
Luca Biferale
Keyword(s):  
Small Scale ◽  
Turbulent Fluctuations

scholarly journals A DNS study of aerosol and small-scale cloud turbulence interaction

2016 ◽  
Author(s):  
N. Babkovskaia ◽  
U. Rannik ◽  
V. Phillips ◽  
H. Siebert ◽  
B. Wehner ◽  
...  
Keyword(s):  
Aerosol Particles ◽  
Vertical Direction ◽  
Relative Number ◽  
Small Scale ◽  
Buoyant Force ◽  
Aerosol Dynamics ◽  
Turbulent Fluctuations ◽  
High Supersaturation ◽  
Scale Turbulence ◽  
Number Of Particles

Abstract. The purpose of this study is to investigate the effect of aerosol dynamics (evaporation/condensation) on atmospheric small-scale turbulence (and vice versa) using direct numerical simulations (DNS). We consider the domain located on the height of about 2000 m from the sea level, experiencing transient high supersaturation due to atmospheric fluctuations of temperature and humidity. To study the effect of aerosol dynamics on the turbulence we vary the total number of particles (Ntot). In turn, to investigate the effect of small-scale turbulence on evolution of aerosol particles we vary the intensity of turbulent fluctuations and the buoyant force. We find that even small amount of aerosol particles (55.5 cm−3) increases the air temperature by 1 K under supersaturated conditions due to release of latent heat. The system comes to an equilibrium faster and the relative number of activated particles appears to be smaller for larger Ntot. We conclude that the presence of aerosol particles results in deceleration of air motion in vertical direction and damping of turbulent fluctuations.

scholarly journals A DNS study of aerosol and small-scale cloud turbulence interaction

2016 ◽  
Vol 16 (12) ◽  
pp. 7889-7898
Author(s):  
Natalia Babkovskaia ◽  
Ullar Rannik ◽  
Vaughan Phillips ◽  
Holger Siebert ◽  
Birgit Wehner ◽  
...  
Keyword(s):  
Air Temperature ◽  
Aerosol Particles ◽  
Vertical Direction ◽  
Relative Number ◽  
Small Scale ◽  
Buoyant Force ◽  
Turbulent Fluctuations ◽  
Microphysical Properties ◽  
Air Motion ◽  
Scale Turbulence

Abstract. The purpose of this study is to investigate the interaction between small-scale turbulence and aerosol and cloud microphysical properties using direct numerical simulations (DNS). We consider the domain located at the height of about 2000 m from the sea level, experiencing transient high supersaturation due to atmospheric fluctuations of temperature and humidity. To study the effect of total number of particles (Ntot) on air temperature, activation and supersaturation, we vary Ntot. To investigate the effect of aerosol dynamics on small-scale turbulence and vertical air motion, we vary the intensity of turbulent fluctuations and the buoyant force. We find that even a small number of aerosol particles (55.5 cm−3), and therefore a small droplet number concentration, strongly affects the air temperature due to release of latent heat. The system comes to an equilibrium faster and the relative number of activated particles appears to be smaller for larger Ntot. We conclude that aerosol particles strongly affect the air motion. In a case of updraught coursed by buoyant force, the presence of aerosol particles results in acceleration of air motion in vertical direction and increase of turbulent fluctuations.

Effect of small-scale turbulent fluctuations on rates of particle formation

2004 ◽  
Vol 35 (5) ◽  
pp. 545-559 ◽  
Author(s):  
C. Housiadas ◽  
Y. Drossinos ◽  
M. Lazaridis
Keyword(s):  
Particle Formation ◽  
Small Scale ◽  
Turbulent Fluctuations
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