Katabatic Winds over Steep Slopes: Overview of a Field Experiment Designed to Investigate Slope-Normal Velocity and Near-Surface Turbulence

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.

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Wave Breaking and Near-Surface Turbulence

10.21236/ada626448 ◽

2002 ◽

Author(s):

David M. Farmer ◽

Johannes Gemmrich

Keyword(s):

Wave Breaking ◽

Near Surface ◽

Surface Turbulence

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Estimation of Air-Sea Gas and Heat Fluxes from Infrared Imagery Based on Near Surface Turbulence Models

Environmental Science and Engineering - Transport at the Air-Sea Interface ◽

10.1007/978-3-540-36906-6_17 ◽

2008 ◽

pp. 241-254 ◽

Cited By ~ 4

Author(s):

Tetsu Hara ◽

Eric VanInwegen ◽

John Wendelbo ◽

Christoph S. Garbe ◽

Uwe Schimpf ◽

...

Keyword(s):

Turbulence Models ◽

Heat Fluxes ◽

Infrared Imagery ◽

Near Surface ◽

Surface Turbulence

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

10.5194/egusphere-egu21-2009 ◽

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

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.

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THEORY OF NEAR SURFACE TURBULENCE APPLIED TO WIND SPEED PROFILES, DRY DEPOSITION, AIR-WATER EXCHANGE, AND CANOPY EFFECTS

Air Dispersion Modeling ◽

10.1002/9781118723098.app3 ◽

2013 ◽

pp. 607-628

Keyword(s):

Wind Speed ◽

Dry Deposition ◽

Water Exchange ◽

Near Surface ◽

Surface Turbulence

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

Atmosphere ◽

10.3390/atmos11090930 ◽

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.

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

Journal of Physical Oceanography ◽

10.1175/2010jpo4491.1 ◽

2011 ◽

Vol 41 (1) ◽

pp. 205-220 ◽

Cited By ~ 17

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.

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Near-surface investigation using additional seismic survey lines: A field experiment

10.1190/segam2017-17723313.1 ◽

2017 ◽

Author(s):

Min Li ◽

Miaoyu Chen ◽

Wei Liu ◽

Meng Zhang ◽

Jiangli Chen ◽

...

Keyword(s):

Surface Investigation ◽

Field Experiment ◽

Seismic Survey ◽

Near Surface

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Impact of terrain heterogeneity on near-surface turbulence structure

Atmospheric Research ◽

10.1016/j.atmosres.2009.06.003 ◽

2009 ◽

Vol 94 (2) ◽

pp. 254-269 ◽

Cited By ~ 14

Author(s):

Clément Fesquet ◽

Philippe Drobinski ◽

Christian Barthlott ◽

Thomas Dubos

Keyword(s):

Turbulence Structure ◽

Near Surface ◽

Surface Turbulence

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FESSTVaL: Field Experiment on sub-mesoscale spatio-temporal variability in Lindenberg – the campaign 2021 an its predecessors

10.5194/ems2021-296 ◽

2021 ◽

Author(s):

Cathy Hohenegger ◽

Felix Ament ◽

Frank Beyrich ◽

Ivan Bastak Duran ◽

Ulrich Löhnert ◽

...

Keyword(s):

Field Experiment ◽

Temporal Variability ◽

Low Cost ◽

Unmanned Aerial Systems ◽

Near Surface ◽

Cold Pools ◽

Measurement Strategy ◽

Meteorological Observatory ◽

Spatio Temporal ◽

Aerial Systems

Measuring submesoscale variability is the core task of the field campaign FESSTVaL (Field Experiment on Sub-Mesoscale Spatio-Temporal Variability in Lindenberg).&#160; FESSTVaL focuses on three sources of submesoscale variability: cold pools, wind gusts and boundary layer pattern. It took place in the summer months of 2021 at the Meteorological Observatory Lindenberg &#8211; Richard-A&#223;mann-Observatory (MOL-RAO) of the German Weather Service (DWD) near Berlin and was initiated by the Hans-Ertel-Center for Weather Research (HErZ).In order to capture phenomena at the submesoscale (500 m &#8211; 5 km), generally not captured by conventional measurement network, a hierarchical measurement strategy is adopted. This includes wind profiling stations with a coordinated scanning strategy of several Doppler Lidars, two mobile profilers to measure thermodynamic properties and precipitation, more than 100 stations with near-surface measurements of air temperature, pressure and soil moisture, more than 20 automatic weather stations, an X-Band radar, and a number of energy balance stations. This equipment is augmented by the extensive ground-based remote sensing array at the MOL-RAO, operated by DWD and by flights operated by Unmanned Aerial Systems. Complementing to this, the benefit of a citizen-science measurement network is investigated during the campaign with &#8220;Internet-of-things&#8221; based technology and low-cost sensors built and maintained by citizens. The measurements are supplemented by high-resolution large-eddy simulations (ICON-LES).Originally planned for the summer 2020, FESSTVaL had to be postponed to 2021 and replaced by three local individual campaigns, conducted in Bayern, Lindenberg and Hamburg in 2020. Those three test campaigns demonstrated the ability of the envisionned measurement strategy and planned instruments to capture submesoscale variability and submesoscale weather phenomean. This talk will give a brief overview on the results of these three campaigns, as a foretaste to FESSTVaL, together with some of the very first measurements taken during FESSTVaL.

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