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

Upwellings, Downdrafts, and Whirlpools: Dominant Structures in Free Surface Turbulence

1994 ◽  
Vol 47 (6S) ◽  
pp. S166-S172 ◽  
Author(s):  
Sanjoy Banerjee
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Wall Turbulence ◽  
Turbulence Structure ◽  
Normal Velocity ◽  
Two Dimensional ◽  
Near Surface ◽  
Surface Turbulence ◽  
Surface Patterns ◽  
Turbulence Generation

Fluid motion at flat, unsheared interfaces develops primarily due to impingement of coherent turbulent structures from the far field. On the other hand, when shear is imposed, alternating low-speed/high-speed regions are formed with ejection-sweep cycles qualitatively similar to those seen in wall turbulence. The transition to this “active” state depends on a shear rate non-dimensionalized by the Reynolds stress and dissipation rate. Turning back to the unsheared (or free) surface case, the bulk turbulence structures cause “upwellings” when they approach the interface. The regions between upwellings appear as stagnation lines on the surface plane—the surface-normal velocity being downwards. Whirlpool-like attached vortices also form at the edges of the upwellings. These attached vortices are remarkably persistent—the main annihilation mechanism being interaction with a subsequent upwelling. For situations where the surface patterns convect away from a region of turbulence generation, i.e. a decaying pattern, the attached vortices become the dominant structure since new upwellings and downdrafts are not formed. The attached vortices pair and decay in a manner such that the near-surface turbulence structure is essentially two-dimensional. Even in situations where turbulence generation occurs quite close to the free-surface, measures such as energy spectra indicate a quasi two-dimensional near-surface structure.

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.

scholarly journals ANÁLISE DA ESTRUTURA VERTICAL DO BALANÇO DE ENERGIA CINÉTICA TURBULENTA DURANTE A OCORRÊNCIA DE EVENTOS DE INTERMITÊNCIA GLOBAL

2016 ◽  
Vol 38 ◽  
pp. 406
Author(s):  
Thaís Freitas Dill ◽  
Adriano Battisti ◽  
Felipe Denardin Costa ◽  
Luiz Eduardo Medeiros ◽  
Viviane Da Silva Guerra
Keyword(s):  
Experimental Data ◽  
Vertical Structure ◽  
Sampling Frequency ◽  
Turbulence Structure ◽  
Shear Surface ◽  
Dominant Term ◽  
Near Surface ◽  
M 10 ◽  
Vertical Turbulence

This study aims to analyze the vertical structure of the terms of the ECT balance equation for the occurrence of intermittent events generated in surface and propagate upward. In order to verify that the dominant terms and the role of each term during such events. It was used FLOSSII experimental data collected in seven vertical levels (1 m, 2 m, 5 m, 10 m, 15 m, 20 m and 30 m) and have a sampling frequency of 60 Hz. The study period comprises between 20 November 2002 to 02 April 2003 and of that total, this study, we analyzed 108 nights. The majority of events generated surface (EB) are very weak compared to the events generated at the top of the tower layer and propagate down. The analyzes made by vertical turbulence structure and ECT balance for the EB’s showed that the dominant term near surface is the mechanical production. Thus, with increasing shear surface, producing turbulence and consequently, the transport of works term “loading” turbulence to higher levels of the atmosphere.

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