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- On the Lagrangian and Eulerian Time Scales of Turbulence Within a
Two-Dimensional Array of Obstacles-
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Abstract: Abstract Fields of Lagrangian ( \(T^{L}\) ) and Eulerian ( \(T^{E}\) ) time scales of the turbulence within a regular array of two-dimensional obstacles of unit aspect ratio have been determined by means of a water-channel experiment reproducing the atmospheric boundary layer in neutral conditions. It has been found that there is a strong spatial inhomogeneity both of the scales and of their ratio, \(\beta = T^{L} /T^{E}\) . The results can provide useful information on numerical modelling of tracer dispersion in urban areas.
PubDate: 2022-09-01
- Celebrating the Career of Dr. John R. Garratt: Long-Term Proponent of
Boundary-Layer Meteorology and International Man of Mystery-
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PubDate: 2022-09-01
- On the Non-monotonic Variation of the Entrainment Buoyancy Flux with Wind
Shear-
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Abstract: Abstract The magnitude of the entrainment buoyancy flux, and hence the growth rate of the convective boundary layer, does not increase monotonically with wind shear. Explanations for this have previously been based on wind-shear effects on the turbulence kinetic energy. By distinguishing between turbulent and non-turbulent regions, we provide an alternative explanation based on two competing wind-shear effects: the initial decrease in the correlation between buoyancy and vertical velocity fluctuations, and the increase in the turbulent area fraction. The former is determined by the change in the dominant forcing; without wind shear, buoyancy fluctuations drive vertical velocity fluctuations and the two are thus highly correlated; with wind shear, vertical velocity fluctuations are partly determined by horizontal velocity fluctuations via the transfer of kinetic energy through the pressure–strain correlation, thus reducing their correlation with the buoyancy field. The increasing turbulent area fraction, on the other hand, is determined by the increasing shear production of turbulence kinetic energy inside the entrainment zone. We also show that the dependence of these conditional statistics on the boundary-layer depth and on the magnitude of the wind shear can be captured by a single non-dimensional variable, which can be interpreted as an entrainment-zone Froude number.
PubDate: 2022-09-01
- Statistical Distribution of Atmospheric Dust Devils on Earth and Mars
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Abstract: Abstract The theoretical foundations of the exponential and power-law analytical formulations for the size–frequency and intensity–frequency distributions of the convective vortices, including dust devils, are re-examined. Jaynes’ general statistical arguments based on Shannon’s entropy maximum principle leading to an exponential distribution are supplemented by Rényi’s maximum entropy principle which is shown to lead to a power-law distribution. In both cases, a key ingredient of the theory is the a priori knowledge of a first finite moment of the distribution. Applications to statistics of convective vortices, including dust devils, on Earth and Mars are discussed. The existence of a finite expectation value of the vortex diameter related to the absolute value of the Obukhov length scale in the atmospheric boundary layer allows a quantitative explanation of a burst of convective vortex activity observed at the InSight landing site in northern autumn on Mars.
PubDate: 2022-09-01
- A Predictive Method for Estimating Space–Time Correlations in the
Atmospheric Surface Layer-
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Abstract: Abstract Space–time correlations are fundamental to statistical theories and turbulence modelling. However, experimental studies of space–time correlations are often restricted to the requirements of high spatially- and temporally-resolved data, especially in the atmospheric surface layer (ASL). In this study, based on the simultaneous multipoint temperature fluctuations measured at different streamwise positions with the application of distributed temperature sensing, the longitudinal space–time correlations of temperature fluctuations (CTT(r, τ)) were directly measured in the near-neutral, unstable, and stable ASL. Our results show that, unlike Taylor’s frozen turbulence hypothesis, the elliptic model can relate the space–time correlation CTT(r, τ) to space correlation (CTT(rE, 0)) in the ASL, where rE = ((r − Ueτ)2 + (Veτ)2)1/2, Ue is the convection velocity, and Ve is the sweeping velocity. Furthermore, we also provide a predictive method for estimating CTT(r, τ) in the ASL based on the elliptic model. With the application of our new method, CTT(r, τ) can be estimated from one-point measurements in the near-neutral, unstable, and stable ASL by using Ue and Ve, and the predicted CTT(r, τ) is similar to the directly measured results. This indicates that our method can be used to reconstruct CTT(r, τ) in the ASL.
PubDate: 2022-09-01
- Horizontal Variations of Nocturnal Temperature and Turbulence Over
Microtopography-
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Abstract: Abstract Nocturnal spatial variation of temperature, wind, and turbulence over microtopography is generally poorly understood. Low amplitude microtopography covers much of the Earth’s surface and, with very stable conditions, can produce significant spatial variations of temperature and turbulence. We examine such variations over gentle terrain that include two shallow gullies that feed into a small valley. The gullies are covered by a sub-network of seven flux stations that is embedded within a larger network that covers the valley. The measurements indicate that gullies of only 2–5-m depth and 100-m width can often lead to spatial variations of temperature of several kelvin or more. Such variations depend on ambient wind speed and direction and the near-surface stratification. We investigate the surprising importance of microscale lee turbulence occurring over the gentle microtopography with slopes of only 5%. Near-surface stratification unexpectedly tends to increase with surface elevation on the slopes. We examine the potential causes of this puzzling behaviour of the near-surface stratification.
PubDate: 2022-09-01
- Quantifying Turbulence Heterogeneity in a Vineyard Using Eddy-Covariance
and Scintillometer Measurements-
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Abstract: Abstract Scintillometry is a non-invasive measurement technique for acquiring spatially-averaged surface heat and moisture fluxes in areas where setting up arrays of instruments can be expensive and logistically difficult. As a path-averaged measurement, scintillometry is a valuable tool for measuring integrated atmospheric turbulence over agricultural terrain where in situ measurements would interfere with farm operations. For this study, a two-wavelength scintillometry system was deployed at an effective height of 7.3 m above ground spanning 749 m over an active vineyard with a canopy height of \(\approx \) 2.15 m. Four eddy-covariance stations were placed strategically throughout the vineyard to capture any spatial heterogeneity. The stations were used to assess whether the spatially-averaged structure parameters of temperature, \(\langle C_{T^2} \rangle \) , and humidity, \(\langle C_{q^2} \rangle \) , adhered to Monin–Obukhov similarity theory (MOST). We derive a new metric, \({\mathscr {D}}\) , to quantify the deviation from homogeneity that describes the nonlinear effects in MOST linking structure parameters and fluxes. This deviation metric gives a physical meaning to the apparent flux overestimation of scintillometry discussed in previous literature. It also facilitates the identification of periods when nonlinear effects are minimal. Using \({\mathscr {D}}\) , we show that the vineyard is homogeneous at the spatial scales of the scintillometer path and use another dataset to emphasize the applicability of \({\mathscr {D}}\) to quantify heterogeneity for a variety of composite surfaces.
PubDate: 2022-09-01
- Observational Investigation of the Statistical Properties of Surface-Layer
Turbulence in a Suburban Area of São Paulo, Brazil: Objective Analysis of
Scaling-Parameter Accuracy and Uncertainties-
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Abstract: Abstract Statistical properties of turbulence, specifically variances of velocity components, temperature, water vapor, and carbon dioxide densities, are observationally characterized using turbulence measurements carried out between 2009 and 2017, at 25.4 m above surface in a suburban area in the metropolitan region of São Paulo (MRSP), Brazil. An objective analysis indicated that the best method to evaluate the zero-plane displacement (d), among five morphometric and anemometric methods is the temperature variance method. A new procedure based on the convergence of these methods is proposed to estimate the accuracy of the aerodynamic parameters. Normalized standard deviation of wind components and scalar properties are described by similarity functions based on Monin–Obukhov similarity theory. Uncertainties in d and Obukhov length are propagated to similarity functions derived for the MRSP and indicated uncertainties of up to 12% (22%) for wind components, 15% (23%) for temperature, 6% (23%) for water vapor and 11% (23%) for carbon dioxide densities during stable (unstable) conditions. By hypothesis testing it was demonstrated that the coefficients of normalized standard deviations of wind components for neutral stability conditions found at MRSP can be considered statistically equal to Roth’s urban averages (Q J R Meteorol Soc126:941–990, 2000), revealing the universal character of these functions. This agreement, added to other evidence, indicates that measurements used in the present study were performed in the inertial sublayer.
PubDate: 2022-08-13
- Comparison of the Sensible Heat Flux Determined by Large-Aperture
Scintillometer and Eddy Covariance Measurements with Respect to the Energy
Balance Problem in the Taklimakan Desert-
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Abstract: Abstract The large-aperture scintillometer (LAS) has been widely used in the estimation of sensible heat fluxes (H) on various land surfaces, but they are seldom used in deserts with dune topographies. Here, an LAS was deployed in the Taklimakan Desert for about two weeks to investigate its ability to estimate H over the dune topography in the desert and its impact on the surface energy balance. We estimated the LAS and eddy covariance (EC) fluxes using standard methods, as well as H directly calculated by the EC system via a spectral fitting method. We conducted a series of sensitivity tests to investigate the scintillometer-based heat flux estimation uncertainties by considering surface and meteorological parameters and surface-layer similarity structure functions. In addition, the imbalance problem in the surface energy budget was examined using the measurements. Desert areas are different from other land surfaces in that they are characterized by a high sensible heat flux. It was found that the LAS had good performance in the Taklimakan Desert and could capture more low-frequency turbulence. Also, the spectral fitting method used on the data obtained with the EC system could capture more low-frequency turbulence compared to the direct calculations made by the EC system. The H values obtained by the LAS (HLAS) were overestimated by about 11.6% relative to those measured by the EC system (HEC), and the HEC values obtained by the spectral fitting method were overestimated by about 12.1% relative to them being directly calculated by the EC system. Large and dispersed values of HLAS/HEC appeared with smaller values of rwT (the correlation coefficient) (i.e., 0.1–0.3), and the large ratio of HLAS/HEC might be related to a predominance of low-frequency motions in stable stratification. However, the H values estimated by the LAS had great uncertainties in the case of high wind speeds and weak winds at night. The main source of uncertainty in the estimation of H by the LAS was the use of the different surface parameters (e.g., the Bowen ratio, roughness length, and LAS effective height) and the different forms of fT(ζ) from the Monin–Obukhov similarity theory (MOST). Different from the flat surfaces in desert areas, dune topography affected the use of fT(ζ) of MOST by 37%. MOST can improve the estimation of H, and then improve the calculation of the surface energy balance ratio (EBR).
PubDate: 2022-08-10
- Uncrewed Aircraft System Measurements of Atmospheric Surface-Layer
Structure During Morning Transition-
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Abstract: Abstract This study applies uncrewed aircraft systems towards the investigation of surface-layer structure during the morning transition. Three uncrewed aircraft systems simultaneously measuring horizontal transects were partnered with a fourth measuring vertical profiles during two consecutive mornings as part of the 2017 Collaboration Leading Operational Unmanned Aerial System Development for Meteorology and Atmospheric Physics (CLOUDMAP) measurement campaign near Stillwater, Oklahoma, USA. Data were analyzed to extract time-dependent single-point statistics of kinematic and thermodynamic variables from the uncrewed aircraft systems. In addition, an approach is presented by which multi-point spatial statistics in the form of auto- and cross-correlations could be calculated from the measurements. The results reflect differences in the evolution of spatial statistics with altitude for each of the two days at scales smaller than 500 m, despite very similar synoptic conditions. Conditional averaging was also applied to identify the structure of sweep and ejection motions and results revealed similarities to observations from canonical wall-bounded flow.
PubDate: 2022-08-05
- Lagrangian Particle Dispersion Models in the Grey Zone of Turbulence:
Adaptations to FLEXPART-COSMO for Simulations at 1 km Grid Resolution-
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Abstract: Abstract Lagrangian particle dispersion models (LPDMs) are frequently used for regional-scale inversions of greenhouse gas emissions. However, the turbulence parameterizations used in these models were developed for coarse resolution grids, hence, when moving to the kilometre-scale the validity of these descriptions should be questioned. Here, we analyze the influence of the turbulence parameterization employed in the LPDM FLEXPART-COSMO model. Comparisons of the turbulence kinetic energy between the turbulence schemes of FLEXPART-COSMO and the underlying Eulerian model COSMO suggest that the dispersion in FLEXPART-COSMO suffers from a double-counting of turbulent elements when run at a high resolution of \(1 \times 1 \,\hbox {km}^2\) . Such turbulent elements are represented in both COSMO, by the resolved grid-scale winds, and FLEXPART, by its stochastic parameterizations. Therefore, we developed a new parametrization for the variations of the winds and the Lagrangian time scales in FLEXPART in order to harmonize the amount of turbulence present in both models. In a case study for a power plant plume, the new scheme results in improved plume representation when compared with in situ flight observations and with a tracer transported in COSMO. Further in-depth validation of the LPDM against methane observations at a tall tower site in Switzerland shows that the model’s ability to predict the observed tracer variability and concentration at different heights above ground is considerably enhanced using the updated turbulence description. The high-resolution simulations result in a more realistic and pronounced diurnal cycle of the tracer concentration peaks and overall improved correlation with observations when compared to previously used coarser resolution simulations (at 7 km \(\times \) 7 km). Our results indicate that the stochastic turbulence schemes of LPDMs, developed in the past for coarse resolution models, should be revisited to include a resolution dependency and resolve only the part of the turbulence spectrum that is a subgrid process at each different mesh size. Although our new scheme is specific to COSMO simulations at \(1 \times 1 \,\hbox {km}^2\) resolution, the methodology for deriving the scheme can easily be applied to different resolutions and other regional models.
PubDate: 2022-08-05
- Dispersive Fluxes Within and Over a Real Urban Canopy: A Large-Eddy
Simulation Study-
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Abstract: Abstract Large-eddy simulations (LES) are conducted to study the transport of momentum and passive scalar within and over a real urban canopy in the City of Boston, USA. This urban canopy is characterized by complex building layouts, densities and orientations with high-rise buildings. Special attention is given to the magnitude, variability and structure of dispersive momentum and scalar fluxes and their relative importance to turbulent momentum and scalar fluxes. We first evaluate the LES model by comparing the simulated flow statistics over an urban-like canopy to data reported in previous studies. In simulations over the considered real urban canopy, we observe that the dispersive momentum and scalar fluxes can be important beyond 2–5 times the mean building height, which is a commonly used definition for the urban roughness sublayer height. Above the mean building height where the dispersive fluxes become weakly dependent on the grid spacing, the dispersive momentum flux contributes about 10–15% to the sum of turbulent and dispersive momentum fluxes and does not decrease monotonically with increasing height. The dispersive momentum and scalar fluxes are sensitive to the time and spatial averaging. We further find that the constituents of dispersive fluxes are spatially heterogeneous and enhanced by the presence of high-rise buildings. This work suggests the need to parameterize both turbulent and dispersive fluxes over real urban canopies in mesoscale and large-scale models.
PubDate: 2022-08-02
- Wavelet Analysis of Coherent Structures Above Maize and Soybean Crops
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Abstract: Abstract Turbulent coherent structures developed in the atmospheric surface layer are responsible for a large part of momentum and scalar fluxes exchanged with canopy layers. Their participation in processes such as evapotranspiration, pathogen infections, mechanical damage due to wind gustiness, modifies crop yield, with generally negative effects. Although South America has a variety of land covers, studies of these subjects are not common in the region. Here, we characterize the time scales of turbulent coherent structures above extensive maize and soybean crops using the wavelet methodology. The role of canopy-height changes associated with crop growth on turbulent structures development is analyzed. The effect of atmospheric stability on the characteristics of the structures detected is also studied. Wavelet analysis shows that both momentum and sensible heat are transported mostly by eddies of 350–400 s periods and also by more intense eddies of 40–50 s period. For momentum fluxes, the former period range prevails under strongly unstable conditions, while the second is present mostly under near-neutral situations. On the contrary, 40–50 s-lasting structures dominate the sensible heat transport under free convection conditions, while longer-lasting eddies transport heat in near-neutral conditions. Stability is the main factor allowing the coherent-structure topological classification, while the crop height is not important. Structures are identified through measurements performed at relative heights greater than those usually discussed in the literature, which indicates the need for further research into coherent-structure modelling.
PubDate: 2022-08-01
- Heat Transfer Through Grass: A Diffusive Approach
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Abstract: Abstract Heat transport through short and closed vegetation such as grass is modelled by a simple diffusion process. The grass is treated as a homogeneous ‘sponge layer’ with uniform thermal diffusivity and conductivity, placed on top of the soil. The temperature and heat-flux dynamics in both vegetation and soil are described using harmonic analysis. All thermal properties have been determined by optimization against observations from the Haarweg climatological station in The Netherlands. Our results indicate that both phase and amplitude of soil temperatures can be accurately reproduced from the vegetation surface temperature. The diffusion approach requires no specific tuning to, for example, the daily cycle, but instead responds to all frequencies present in the input data, including quick changes in cloud cover and day–night transitions. The newly determined heat flux at the atmosphere–vegetation interface is compared with the other components of the surface energy balance at this interface. The budget is well-closed, particularly in the most challenging cases with varying cloud cover and during transition periods. We conclude that the diffusion approach (either implemented analytically or numerically) is a physically consistent alternative to more ad hoc methods, like ‘skin resistance’ approaches for vegetation and bulk correction methods for upper soil heat storage. However, more work is needed to evaluate parameter variability and robustness under different climatological conditions. From a numerical perspective, the present representation of vegetation allows for both slow and rapid feedbacks between the atmosphere and the surface. As such, it would be interesting to couple the present surface parametrization to turbulence-resolving models, such as large-eddy simulations.
PubDate: 2022-08-01
- A Framework for Uncertainty Quantification in One-Dimensional Plant Canopy
Flow-
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Abstract: Abstract Although the fidelity of computational-fluid-dynamics (CFD) models for the study of flow in plant canopies has significantly increased over the past decades, the inability to exactly measure the canopy structure and its material and physiological properties introduces a degree of uncertainty in model results that is often difficult to quantify. The present work addresses this problem by proposing a Bayesian uncertainty quantification (UQ) framework for evaluating the impact of uncertain canopy geometry on selected microscale flow statistics (the quantities of interest, QoIs, of the problem). The framework links available in-situ measurements of flow statistics to the uncertainty stemming from foliage spatial distribution and orientation, as well as from the aerodynamic plant response. The uncertainty is first characterized via a Markov chain Monte Carlo procedure, and then propagated to the QoIs through the Monte Carlo sampling method, which returns mean profiles and two-standard-deviation-(2SD-)intervals for the QoIs. The UQ framework relies on a one-dimensional CFD solver to simulate the flow over the Duke Forest, located near Durham, North Carolina, USA. Model results are compared against a standard deterministic solution in terms of mean velocity, Reynolds stress and turbulence-kinetic-energy profiles, as well as canopy aerodynamic parameters. For the considered QoIs, it is found that the 2SD-intervals obtained with the UQ procedure cover \(80\%\) of the experimental intervals, whereas the deterministic solution overlaps with only \(47 \%\) of them. Overall, this study highlights the potential of UQ to advance CFD capabilities for predicting exchange processes between realistic plant canopies and the surrounding atmosphere.
PubDate: 2022-07-29
- Flux–Gradient Relationships Below 2 m Over a Flat Site in Complex
Terrain-
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Abstract: Abstract The surface–atmosphere turbulent exchange fluxes are experimentally determined using the eddy-covariance method. Their estimation using profiles of the variables of interest is a less costly alternative, although restricted to certain ranges of stability and assumed to hold for relatively flat and homogeneous terrain. It relays usually on the prescription of the roughness lengths for momentum, heat and matter, the latter two being adjustable parameters with unclear physical significance. The relations are derived with data from screen level to a few tens of metres upward. The application of these expressions using data only at one level in the surface layer implies assuming zero wind speed and the land surface temperature at their respective roughness lengths. The latter is a quantity that experimentally can only be determined radiatively with a substantial uncertainty. In this work the flux-profile relationships for momentum and sensible heat are assessed over a flat site in moderately inhomogeneous complex terrain in the southern pre-Pyrenees, using data between 2 m and the surface. The main findings are that (i) the classical expressions hold in the daytime for most of the dataset, (ii) the iterative estimations using the Obukhov length and the direct ones using the bulk Richardson number provide very similar results, (iii) using a second observation of temperature avoids a radiometric measure of land surface temperature and the prescription of a thermal roughness length value, (iv) the estimations over wet terrain with high irradiance depart largely from observations.
PubDate: 2022-07-07
- Analysis of Observational Characteristic Features of the Eulerian
Autocorrelation Function in Low and Moderate Wind Conditions-
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Abstract: Abstract Turbulent data from three sites are utilized to analyze the characteristic features of the Eulerian autocorrelation function (EAF) of horizontal (longitudinal and lateral) wind components and temperature under different regimes of wind speed and near-surface atmospheric stability. It is shown that classical formulations do not adequately describe the observed EAF behaviour and are unable to capture the peak of the significant negative observed lobe. These formulations are modified by introducing a phase angle \(\alpha\) to make them consistent with the observations. The modified formulations are shown to better characterize the behaviour of the EAF curve and its absolute value of significant negative lobe ( \(\left {R}_{Min}\right \) ) for both low and moderate wind conditions for all three datasets. Further, a new parametrization for the meandering parameter m is proposed in terms of the observed value of \(\left {R}_{Min}\right \) without using any formulations for the EAF. It is found that the majority of low and moderate wind data belong to the significant meandering range, although the extent of meandering is found to be relatively more pronounced at low wind speeds as compared to moderate wind speeds. The occurrence of meandering (low-frequency horizontal wind oscillations) is found to be independent of stability, topography, and geographical location.
PubDate: 2022-07-01
- Evaluation of the SPARTACUS-Urban Radiation Model for Vertically Resolved
Shortwave Radiation in Urban Areas-
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Abstract: Abstract The heterogenous structure of urban environments impacts interactions with radiation, and the intensity of urban–atmosphere exchanges. Numerical weather prediction (NWP) often characterizes the urban structure with an infinite street canyon, which does not capture the three-dimensional urban morphology realistically. Here, the SPARTACUS (Speedy Algorithm for Radiative Transfer through Cloud Sides) approach to urban radiation (SPARTACUS-Urban), a multi-layer radiative transfer model designed to capture three-dimensional urban geometry for NWP, is evaluated with respect to the explicit Discrete Anisotropic Radiative Transfer (DART) model. Vertical profiles of shortwave fluxes and absorptions are evaluated across domains spanning regular arrays of cubes, to real cities (London and Indianapolis). The SPARTACUS-Urban model agrees well with the DART model (normalized bias and mean absolute errors < 5.5%) when its building distribution assumptions are fulfilled (i.e., buildings randomly distributed in the horizontal). For realistic geometry, including real-world building distributions and pitched roofs, SPARTACUS-Urban underestimates the effective albedo (< 6%) and ground absorption (< 16%), and overestimates wall-plus-roof absorption (< 15%), with errors increasing with solar zenith angle. Replacing the single-exponential fit of the distribution of building separations with a two-exponential function improves flux predictions for real-world geometry by up to half. Overall, SPARTACUS-Urban predicts shortwave fluxes accurately for a range of geometries (cf. DART). Comparison with the commonly used single-layer infinite street canyon approach finds SPARTACUS-Urban has an improved performance for randomly distributed and real-world geometries. This suggests using SPARTACUS-Urban would benefit weather and climate models with multi-layer urban energy balance models, as it allows more realistic urban form and vertically resolved absorption rates, without large increases in computational cost or data inputs.
PubDate: 2022-06-29
- On the Influence of Large-Scale Atmospheric Motions on Near-Surface
Turbulence: Comparison Between Flows Over Low-Roughness and Tall
Vegetation Canopies-
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Abstract: Abstract Contrary to Monin–Obukhov similarity theory, near-surface atmospheric turbulence depends not only on local motions but also on larger-scale motions associated with the full atmospheric boundary layer (ABL), where they themselves evolve in character with thermal stratification. After reviewing our current knowledge of ABL motions, we present wavelet velocity and air temperature spectra for both eddy-surface-layer (ESL) flows above rough surfaces and roughness-sublayer (RSL) flows above vegetation canopies, both flows characterizing turbulence over two scales of land roughness. Spectra are extended to the production scale to identify the influence of ABL-scale motions following the thermal stratification. Contrary to turbulence in the ESL, RSL turbulence appears weakly enhanced by ABL-scale motions in near-neutral regimes. With increasing influence of buoyancy, ABL-scale motions play a larger role in ESL and RSL flows, dominating the locally produced turbulence in free convection, while acting to decouple local from the large-scale motions in the stable regime. The behaviour of ESL and RSL spectra with stability variations support the view of, (1) canopy-scale eddies dominating the canopy turbulence over the larger ABL-scale motions in windy conditions, (2) ABL-scale motions known as very-large-scale motions (VLSMs) influencing the ESL horizontal velocity turbulence in windy conditions, and (3) the progressive transitioning of ABL-scale motions from VLSMs to thermals with instability in ESL flows. The direct contribution of ABL-scale motions to near-surface momentum and heat turbulent fluxes appears small. Finally, near-surface velocity spectra are well-approximated as a linear superposition of individual spectra associated to the main eddies populating the flow.
PubDate: 2022-06-06
DOI: 10.1007/s10546-022-00710-z
- Turbulence characteristics within the atmospheric surface layer of the
coastal region of Qatar-
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Abstract: Abstract The atmospheric turbulence characteristics in the coastal region of Qatar are analyzed using the measurements conducted on the shoreline (26.08 N, 51.36 E). The micrometeorological data were collected, from August 2015 to September 2016, using sonic anemometers (20 Hz) at three heights and a weather station atop a 9-m tower. The turbulence characteristics are studied within the framework of Monin–Obukhov similarity theory (MOST), in the presence of the coastal inhomogeneities generated by the sea and land surfaces coming together. The results show the wind from the north-west prevails during the entire test period, with the wind speed higher than that from other directions. The non-dimensional standard deviations of velocity components are found to be consistent the results reported around the world and match suggested MOST scaling, with a relatively greater value for the dissipation rate of turbulent kinetic energy. The flux Richardson number shows a larger scatter under the super-stable and super-unstable regimes. Moreover, the non-dimensional standard deviation of temperature does not align with the suggested model under near-neutral and very stable regimes, and the gradient Richardson number shows some negative values under stable regimes. Two different atmospheric daily stability patterns, ‘orderly’ and ‘disheveled,’ are identified based on the wind conditions. The orderly stability pattern shows a daily descending and ascending trend during the sunrise and sunset periods, respectively, while the disheveled days follow a random pattern with no clear order. The two patterns are then related to the wind continuity and direction relative to the shoreline.
PubDate: 2022-06-03
DOI: 10.1007/s10546-022-00709-6
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