Near-surface turbulence effects on electro-optical propagation in an arid environment

2019 ◽  
Author(s):  
Christian Eisele ◽  
Dirk P. Seiffer ◽  
Erik Sucher ◽  
Carmen Ullwer ◽  
Thomas Kociok ◽  
...  
Keyword(s):  
Arid Environment ◽  
Near Surface ◽  
Optical Propagation ◽  
Surface Turbulence ◽  
Turbulence Effects

Wave Breaking and Near-Surface Turbulence

2002 ◽  
Author(s):  
David M. Farmer ◽  
Johannes Gemmrich
Keyword(s):  
Wave Breaking ◽  
Near Surface ◽  
Surface Turbulence

Characterization of near-surface turbulence in the stable atmosphere of the Alpine Inn Valley

2021 ◽  
Author(s):  
Manuela Lehner ◽  
Mathias W. Rotach
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Intermittent Turbulence ◽  
Near Surface ◽  
Stable Conditions ◽  
Surface Turbulence ◽  
Thermally Driven ◽  
Wind Profiles ◽  
Temperature Inversions ◽  
Sky Conditions

<p>The stable boundary layer is typically characterized by weak and sometimes intermittent turbulence, particularly under very stable conditions. In mountain valleys, nocturnal temperature inversions and cold-air pools form frequently under synoptically undisturbed and clear-sky conditions, which will dampen turbulence. On the other hand, thermally driven slope and valley winds form under the same conditions, which interact with each other and are both characterized by jet-like wind profiles, thus resulting in both horizontal and vertical wind shear, which creates a persistent source for turbulence production. Data will be presented from six flux towers in the Austrian Inn Valley, which are part of the i-Box measurement platform, designed to study near-surface turbulence in complex, mountainous terrain. The six sites are located within an approximately 6.5-km long section of the 2-3-km wide valley approximately 20 km east of Innsbruck. The data are analyzed to characterize the strength and intermittency of turbulence kinetic energy and turbulent fluxes across the valley and to determine whether the persistent wind shear associated with thermally driven flows is sufficient to generate continuous turbulence.</p>

scholarly journals Influence of Complex Terrain on Near-Surface Turbulence Structures over Loess Plateau

Atmosphere ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 930
Author(s):  
Jiening Liang ◽  
Qi Guo ◽  
Zhida Zhang ◽  
Min Zhang ◽  
Pengfei Tian ◽  
...  
Keyword(s):  
Loess Plateau ◽  
Complex Terrain ◽  
Longitudinal Velocity ◽  
Complex Topography ◽  
Horizontal Scale ◽  
Flux Footprint ◽  
Near Surface ◽  
Turbulence Structures ◽  
Vertical Scale ◽  
Surface Turbulence

To study the influence of complex terrain with different scales on the structure of near-surface turbulence, the turbulence observational data from Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) were analyzed. SACOL is located in typical Loess Plateau topography. The terrain around the site varies greatly with the direction. Representative data from the Northeast, Southeast, Southwest, and Northwest were selected to study the structure characteristics of the near surface turbulence. The complex topography within the flux footprint enhances the vertical scale of turbulence σw and thereby increases the vertical–longitudinal ratio of turbulence Ar. While the turbulent horizontal scale σu is also significantly affected by the distant terrain beyond the flux footprint. The upwind terrain undulation increases σu and reduces Ar. Affected by the complex terrain, the ratio of the spectrum of the vertical velocity to that of the longitudinal velocity, Sw(n)/Su(n), is far less than 4/3 in the southwest direction, and the turbulence is significantly anisotropic.

The Effects of Small-Scale Turbulence on Air–Sea Heat Flux

2011 ◽  
Vol 41 (1) ◽  
pp. 205-220 ◽  
Author(s):  
Fabrice Veron ◽  
W. Kendall Melville ◽  
Luc Lenain
Keyword(s):  
Field Experiments ◽  
Renewal Theory ◽  
Small Scale ◽  
Surface Renewal ◽  
Near Surface ◽  
Turbulence Measurements ◽  
Renewal Time ◽  
Surface Turbulence ◽  
The Mean ◽  
Renewal Events

Abstract The air–sea exchange of heat is mainly controlled by the molecular diffusive layer adjacent to the surface. With an order of magnitude difference between the kinematic viscosity and thermal diffusivity of water, the thermal sublayer is embedded within its momentum analog: the viscous sublayer. Therefore, the surface heat exchange rates are greatly influenced by the surface kinematics and dynamics; in particular, small-scale phenomena, such as near-surface turbulence, have the greatest potential to affect the surface fluxes. Surface renewal theory was developed to parameterize the details of the turbulent transfer through the molecular sublayers. The theory assumes that turbulent eddies continuously replace surface water parcels with bulk fluid, which is not in equilibrium with the atmosphere and therefore is able to transfer heat. The so-called controlled-flux technique gives direct measurements of the mean surface lifetime of such surface renewal events. In this paper, the authors present results from field experiments, along with a review of surface renewal theory, and show that previous estimates of air–sea scalar fluxes using the controlled-flux technique may be erroneous if the probability density function (PDF) of surface renewal time scales is different from the routinely assumed exponential distribution. The authors show good agreement between measured and estimated heat fluxes using a surface renewal PDF that follows a χ distribution. Finally, over the range of forcing conditions in these field experiments, a clear relationship between direct surface turbulence measurements and the mean surface renewal time scale is established. The relationship is not dependent on the turbulence generation mechanism. The authors suggest that direct surface turbulence measurements may lead to improved estimates of scalar air–sea fluxes.

Mineralogy of the near-surface expression of Au-As-Cu mineralization in an arid environment

1994 ◽  
Vol 58 (391) ◽  
pp. 315-323
Author(s):  
R. Bogoch ◽  
M. Shirav ◽  
A. Gilat ◽  
L. Halicz
Keyword(s):  
Iron Oxide ◽  
Surface Expression ◽  
Arid Environment ◽  
Solid Solution Phase ◽  
Near Surface ◽  
Amorphous Phases ◽  
Fine Grained ◽  
Precambrian Terrain ◽  
Spherical Droplets ◽  
Neutral Conditions

AbstractIn the arid, Late Precambrian terrain of southern Israel, a complex suite of minerals and amorphous species were deposited in host gneiss from fluids under near-neutral conditions within 1 m of the surface. The morphology of secondary gold appears to relate to its host mineral (skeletal-dendritic with quartz; multi-faceted crystals with arsenates; spherical droplets with iron oxide). The gold is very fine-grained, and was most likely complexed as a thiosulphate.Three amorphous phases are present (iron oxide, chrysocolla, Cu-Mn-(Fe-As) silicate). At least in part, gold and baryte appear to have crystallized out of a metal-Fe-oxide gel. Other minerals, including apatite, anglesite, and conichalcite, may have grown from appropriate crystallites present in the gel.The conichalcite occurs mainly as bladed to acicular radial spherulites. In the presence of lead, a solid solution phase between duftite and conichalcite (‘Pb-conichalcite’) was formed.

Impact of terrain heterogeneity on near-surface turbulence structure

2009 ◽  
Vol 94 (2) ◽  
pp. 254-269 ◽  
Author(s):  
Clément Fesquet ◽  
Philippe Drobinski ◽  
Christian Barthlott ◽  
Thomas Dubos
Keyword(s):  
Turbulence Structure ◽  
Near Surface ◽  
Surface Turbulence

scholarly journals The Nature of Atmospheric Turbulence Effects on Imaging and Pseudo-Imaging Systems, and its Quantification

1979 ◽  
Vol 50 ◽  
pp. 4-1-4-44
Author(s):  
David L.
Keyword(s):  
Atmospheric Turbulence ◽  
Speckle Interferometry ◽  
Optical Propagation ◽  
Body Of Knowledge ◽  
Wavefront Distortion ◽  
Turbulence Effects ◽  
Atmospheric Turbulence Effects ◽  
Extensive Body ◽  
Proper Interpretation ◽  
Optical Strength

AbstractOver the last two decades, an extensive body of knowledge has been developed concerning the effects of atmospheric turbulence on optical propagation. Much of this is directly relevant to astronomical imaging, and with proper interpretation, to the type of pseudo-imagery that is of concern to us at this conference. This paper will provide an overview of this matter, hopefully with sufficient insight developed that the reader will be able to quickly estimate the nature and magnitude of the turbulence effects to be expected in a pseudo-imagery process. The paper starts with a review of turbulence effects on conventional imagery, reviewing the “nondimensional” nature of the turbulence statistics, presenting the local measure of the optical strength of turbulence,, and developing the resolution scale, r0. It presents a statistical view of the nature of the wavefront distortion geometry, indicating the dominance of the random wavefront tilt component. The MTF for conventional imagery and for speckle interferometry (Labeyrie) is presented with comments concerning their relationship. Following that, the foundation of the speckle imagery concept (Knox-Thompson) is presented. Results are then set forth for the allowable spectral bandwidth in speckle techniques, as well as results defining the allowable field-of-view size (isoplanatism) and the allowable exposure time for speckle techniques. Taken all together, these results provide a basis for estimating most of the significant effects of atmospheric turbulence in speckle interferometry and speckle imagery.

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