Stable Atmospheric Boundary Layer Research Articles

Effect Dynamic Stability of Atmospheric Boundary Layer on Plume Downward Flux Emitted from Daura Refinery Stacks

The vertical motion of air that enhances or restricts the atmospheric turbulence through atmospheric boundary layer is known as "atmospheric stability", in which any movement of atmospheric components such as water vapor, aerosols, etc. are affected by the atmospheric stability. The aim of this research is to test the effect of atmospheric boundary layer stability on the amount of downward aersols flux at 10um (PM10) emission from stacks of Daura refinery, and estimated of deposition dust aerosols PM10 amount in area around the Daura refinery. In this study, hourly atmospheric stability based on similar theory of Monin-Obukhov length is calculated from archived data of the European Center for Medium Range Weather Forecast, and deposition velocity (Vd) for PM10 that is emitted from stacks Daura Refinery is calculated using the stability parameter (L). PM10 concentration is estimated according to the Gaussian model, which is used along with deposition velocity at this partical size in order to produce downward sedimentation flux (Fp) at distances 1000, 5000 and 10000 m from stack point sources emission. Results show that areas located to the south and southeast of the refinery receive large amounts of deposited flux values through stable weather conditions, where the accumulated PM10 amounts during one month have recorded 1.5 million μg /m2.s in January at a distance of 1000 m from refinery center stacks, while this amount reaches 532 million μg/m2.s during July due to the high emission rates resulting from burning fuel oil during July. The percentages of PM10 sedimentation decreased with the distance from the refinery to 1712 and 322839 μg /m2.s at a distance 10 km from the refinery in January and July, respectively. According to this method, the accumulated amount of PM10 in square meters can be estimated at any time, if atmospheric stability conditions and the domain of wind direction are known.

The simplified $$k-\epsilon $$ turbulence model applied to numerical simulation of the stable atmospheric boundary layer

The simplified $$k-\epsilon $$ turbulence model applied to numerical simulation of the stable atmospheric boundary layer

Local dimensionality and inverse persistence analysis of atmospheric turbulence in the stable boundary layer.

The dynamics across different scales in the stable atmospheric boundary layer has been investigated by means of two metrics, based on instantaneous fractal dimensions and grounded in dynamical systems theory. The wind velocity fluctuations obtained from data collected during the Cooperative Atmosphere-Surface Exchange Study-1999 experiment were analyzed to provide a local (in terms of scales) and an instantaneous (in terms of time) description of the fractal properties and predictability of the system. By analyzing the phase-space projections of the continuous turbulent, intermittent, and radiative regimes, a progressive transformation, characterized by the emergence of multiple low-dimensional clusters embedded in a high-dimensional shell and a two-lobe mirror symmetrical structure of the inverse persistence, have been found. The phase space becomes increasingly complex and anisotropic as the turbulent fluctuations become uncorrelated. The phase space is characterized by a three-dimensional structure for the continuous turbulent samples in a range of scales compatible with the inertial subrange, where the phase-space-filling turbulent fluctuations dominate the dynamics, and is low dimensional in the other regimes. Moreover, lower-dimensional structures present a stronger persistence than the higher-dimensional structures. Eventually, all samples recover a three-dimensional structure and higher persistence level at large scales, far from the inertial subrange. The two metrics obtained in the analysis can be considered as proxies for the decorrelation time and the local anisotropy in the turbulent flow.

Numerical Simulation of Atmospheric Boundary Layer Turbulence in a Wind Tunnel Based on a Hybrid Method

In the Computational Fluid Dynamics (CFD) simulation for building structures, it is important to generate a stable atmospheric boundary layer (ABL) flow field that meets the standards. In this paper, the wind profile, turbulence intensity, and wind velocity power spectrum in the target region of a numerical wind tunnel were accurately simulated by a hybrid method. With the numerical simulation software FLUENT, the hybrid simulation method was implemented. In the hybrid simulation method, the wind field was simulated by setting the roughness element in the upstream of the model, adding random disturbance, and setting the circulation surface. The influences of simulation parameters (such as roughness element and random number parameters) and FLUENT solution methods on the flow field results were studied. The results show that the influence range of the roughness element on turbulence intensity is approximately 6 times its physical height. The turbulence intensity is positively correlated with the standard deviation of random numbers and negatively correlated with the assignment height. Finally, the wind fields for different terrains satisfying the standards were obtained in numerical wind tunnels. A simulation of the wind pressure on an inflatable membrane structure was illustrated. The comparison between numerical and experimental results shows a good accordance, which indicates a desirable potential in practical application.

Impact of Clouds and Blowing Snow on Surface and Atmospheric Boundary Layer Properties Over Dome C, Antarctica.

Clouds and blowing snow (BLSN) occur frequently over Antarctica, where it is critical to understand their feedbacks to surface and atmospheric boundary layer processes. Dome C, an elevated East Antarctic station, dominated by lengthy periods of surface longwave (LW) radiative cooling, is selected to reveal cloud and BLSN impacts within a largely stable environment. The sky condition is classified as clear, cloudy, or BLSN, using 3years of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations satellite data. Co-located and contemporaneous in situ observations are used to investigate the relationship of sky condition with surface and atmospheric boundary layer thermal structure, focusing on seasonal variability. Results show that increased downwelling LW radiation from clouds abate surface radiative cooling losses, contributing to warming during all seasons. An increase of 3°C in the mean surface air temperature is observed during spring, whereas, a more dramatic rise (around 10°C), due to accompanying large-scale subsidence, is observed during fall and winter in association with clouds. For all seasons, the wind speed and wind speed shear are strongest during BLSN events, and the surface-based inversion is weakened by cooling which peaks in a shallow above-surface turbulent layer. The stronger background stability during fall and winter seasons, restricts turbulence and BLSN depths generally to the lowest tens of meters. The Earth's cryosphere is among the most rapidly evolving yet least well-observed regions, and knowledge of clouds and BLSN interactions with the typical stable atmospheric boundary layer can help further understand energy and moisture exchanges.

Water Vapor Flux‐Profile Relationship in the Stable Boundary Layer Over the Sea Surface

AbstractComprehensive marine atmospheric turbulence observation data, meteorological sounding and sea surface conditions in the South China Sea were employed to analyze and parameterize the vapor profile in the stable marine atmospheric boundary layer. The observations involved a three‐dimensional ultrasonic anemometer, water vapor carbon dioxide analyzer, radiosonde, and buoy. This paper theoretically determined that the water vapor profile function φq differs from the temperature profile function φh and that φq should be independently parameterized. A linear relationship existed between the dimensionless water vapor gradient and stability parameters based on the observation results, and φq was then obtained as φq(z/L) = az/L + b, in which the stability covered the stability range (z/L > 1). This result was applied in the Tropical Ocean‐Global Atmosphere Coupled‐Ocean Atmosphere Response Experiment bulk flux algorithm, and the simulation of the latent heat flux was improved.

Wind farm blockage in a stable atmospheric boundary layer

Wind farm blockage is the flow deceleration in front of a large turbine array, due to which the first wind farm row produces less power than a corresponding solitary row. Understanding wind farm blockage is crucial as a failure to accurately model the effect leads to a systematic difference between the modeled and actual wind farm performance. While stable atmospheric conditions are known to impact wind farm performance, the effect on wind farm blockage is not well understood. We use large eddy simulations to investigate blockage in a stably stratified atmospheric boundary layer without capping inversion by systematically varying the streamwise turbine spacing and the surface cooling rate. We consider stable boundary layers without capping inversion as it allows us to isolate the effect of surface stability. Primarily, we demonstrate that wind farm blockage increases with atmospheric stability due to the deflection of relatively cold flow over the wind farm. Displacement of this high-density colder air creates a high-pressure region at the wind farm entrance. The formation of the high-pressure region enhances the adverse pressure gradient and increases the flow deceleration in front of the wind farm under stable atmospheric conditions.

Effects of natural surfactants on the spatial variability of surface water temperature under intermittent light winds on Lake Geneva

The spatial variability of lake surface water temperature (LSWT) between smooth and rough surface areas and its potential association with the natural surfactant distribution in the surface microlayer were investigated for the first time in a lake. In spring 2019, two different field campaigns were carried out in Lake Geneva to measure: i) the enrichment factor of fluorescent dissolved organic matter (FDOM) as a proxy for biogenic surfactants, and ii) LSWT and near-surface water temperature profiles while simultaneously monitoring water surface roughness in both cases. Results indicate that, under intense incoming short-wave radiation and intermittent light wind conditions, the atmospheric boundary layer (ABL) was stable and the accumulation of heat due to short-wave radiation in near-surface waters was greater than heat losses by surface cooling, thus creating a diurnal warm layer with strong thermal stratification in the water near-surface layer. A threshold wind speed of 1.5 m s-1 was determined as a transition between different dynamic regimes. For winds just above 1.5 m s-1, the lake surface became patchy, and smooth surface areas (slicks) were more enriched with FDOM than rough areas (non-slick) covered with gravity-capillary waves (GCW). Sharp thermal boundaries appeared between smooth and rough areas. LSWT in smooth slicks was found to be more than 1.5°C warmer than in rough non-slick areas, which differs from previous observations in oceans that reported a slight temperature reduction inside slicks. Upon the formation of GCW in non-slick areas, the near-surface stratification was destroyed and the surface temperature was reduced. Furthermore, winds above 1.5 m s-1 continuously fragmented slicks causing a rapid spatial redistribution of LSWT patterns mainly aligned with the wind. For wind speeds below 1.5 m s‑1 the surface was smooth, no well-developed GCW were observed, LSWT differences were small, and strong near-surface stratification was established. These results contribute to the understanding and the quantification of air-water exchange processes, which are presently lacking for stable Atmospheric Boundary Layer conditions in lakes.

Improved Representation of Horizontal Variability and Turbulence in Mesoscale Simulations of an Extended Cold-Air Pool Event

Abstract Cold-air pools (CAPs), or stable atmospheric boundary layers that form within topographic basins, are associated with poor air quality, hazardous weather, and low wind energy output. Accurate prediction of CAP dynamics presents a challenge for mesoscale forecast models in part because CAPs occur in regions of complex terrain, where traditional turbulence parameterizations may not be appropriate. This study examines the effects of the planetary boundary layer (PBL) scheme and horizontal diffusion treatment on CAP prediction in the Weather Research and Forecasting (WRF) Model. Model runs with a one-dimensional (1D) PBL scheme and Smagorinsky-like horizontal diffusion are compared with runs that use a new three-dimensional (3D) PBL scheme to calculate turbulent fluxes. Simulations are completed in a nested configuration with 3-km/750-m horizontal grid spacing over a 10-day case study in the Columbia River basin, and results are compared with observations from the Second Wind Forecast Improvement Project. Using event-averaged error metrics, potential temperature and wind speed errors are shown to decrease both with increased horizontal grid resolution and with improved treatment of horizontal diffusion over steep terrain. The 3D PBL scheme further reduces errors relative to a standard 1D PBL approach. Error reduction is accentuated during CAP erosion, when turbulent mixing plays a more dominant role in the dynamics. Last, the 3D PBL scheme is shown to reduce near-surface overestimates of turbulence kinetic energy during the CAP event. The sensitivity of turbulence predictions to the master length-scale formulation in the 3D PBL parameterization is also explored. Significance Statement In this article, we demonstrate how a new framework for modeling atmospheric turbulence improves cold pool predictions, using a case study from January 2017 in the Columbia River basin (U.S. Pacific Northwest). Cold pools are regions of cold, stagnant air that form within valleys or basins, and improved forecasts could help to mitigate the risks they pose to air quality, transportation, and wind energy production. For the chosen case study, our tests show a reduction in temperature and wind speed errors by up to a factor of 2–3 relative to standard model options. These results strongly motivate continued development of the framework as well as its application to other complex weather events.

A flexible actuator curve model for aeroelastic simulations of wind turbines in atmospheric boundary layers

The current trend of wind turbine upscaling has led to the use of long and slender blades prone to large structural deformations. In the present study, the impact of the aeroelastic effects is assessed for the NREL-5MW wind turbine in a turbulent wind. To this end, an actuator curve method coupled to a one-dimensional finite-element structural solver is implemented in a fourth-order finite difference code that can perform large eddy simulation (LES) of realistic winds. The approach is computationally affordable compared to blade-resolved simulations and hence long time series can be computed. This, combined to the ability of the LES to capture the relevant scales of the unsteadiness wind, leads to a better estimation of the fluctuating loads and power of the turbine. The results are here shown for one and two wind turbines operating in a neutrally stable atmospheric boundary layer. It appears that the blade mostly deforms according to its first bending mode. The rotation of the blade in the sheared atmospheric flow is responsible for large amplitude deformations, but the turbulence also plays a role in causing deformations at higher frequencies with a smaller amplitude. The azimuthal distributions of loads and of power are significantly affected when the aeroelasticity is considered.

Large-eddy-simulation study on turbulent particle deposition and its dependence on atmospheric-boundary-layer stability

Abstract. It is increasingly recognized that atmospheric-boundary-layer stability (ABLS) plays an important role in eolian processes. While the effects of ABLS on particle emission have attracted much attention and been investigated in several studies, those on particle deposition have so far been less well studied. By means of large-eddy simulation, we investigate how ABLS influences the probability distribution of surface shear stress and hence particle deposition. Statistical analysis of the model results reveals that the shear stress can be well approximated using a Weibull distribution, and the ABLS influences on particle deposition can be estimated by considering the shear stress fluctuations. The model-simulated particle depositions are compared with the predictions of a particle-deposition scheme and measurements, and the findings are then used to improve the particle-deposition scheme. This research represents a further step towards developing deposition schemes that account for the stochastic nature of particle processes.

The stable atmospheric boundary layer over snow‐covered sea ice: Model evaluation with fine‐scale ISOBAR18 observations

AbstractA realistic representation of the stable atmospheric boundary layer in numerical weather prediction (NWP) and climate models is still a challenge. We study the evolution of a stable boundary layer over snow‐covered sea ice in Bothnian Bay during wintertime in 2018. We perform high‐resolution model experiments with the Weather Research and Forecasting model in its single‐column model configuration and its default mesoscale configuration to assess which physical processes are essential to predict near‐surface variables correctly. We evaluate our model runs against the unique observational dataset collected during ISOBAR18, which combines novel, upper‐air measurements by an uncrewed aircraft system with wind lidar, sodar, and conventional meteorological mast data. By analysing surface fluxes in the single‐column model, we demonstrate how the atmospheric cooling at the ground can be modelled more realistically than in the mesoscale set‐up. We show that surface albedo and sea‐ice thickness are essential for the surface energy balance in the model, and we demonstrate how the surface fluxes in the mesoscale downscaling with default settings are subject to strong biases. We also show that the ERA5 reanalysis is not capable of representing the observed surface meteorology in the stable atmospheric boundary layer. Our study illustrates the importance of surface albedo and sea‐ice thickness for NWP models. Though a seasonal snow albedo is already in use in many NWP settings, the routine inclusion of sea‐ice thickness, in particular, would be a great step forward for weather forecasts and regional climate simulations.

Study of Coastal Effects Relevant for Offshore Wind Energy Using Spaceborne Synthetic Aperture Radar (SAR)

Coastal wind speed gradients relevant for offshore windfarming are analysed based on synthetic aperture radar (SAR) data. The study concentrates on situations with offshore wind directions in the German Bight using SAR scenes from the European satellites Sentinel-1A and Sentinel-1B. High resolution wind fields at 10 m height are derived from the satellite data set and respective horizontal wind speed gradients are investigated up to about 170 km offshore. The wind speed gradients are classified according to their general shape with about 60% of the cases showing an overall increase of wind speeds with growing distance from the coast. About half of the remaining cases show an overall wind speed decrease and the other half a decrease with a subsequent increase at larger distances from the coast. An empirical model is fitted to the horizontal wind speed gradients, which has three main parameters, namely, the wind speed over land, the equilibrium wind speed over sea far offshore, and a characteristic adjustment length scale. For the cases with overall wind speed increase, a mean absolute difference of about 2.6 m/s is found between wind speeds over land and wind speeds far offshore. The mean normalised wind speed increase with respect to the land conditions is estimated as 40%. In terms of wind power density at 10 m height this corresponds to an absolute average growth by 0.3 kW/m2 and a normalised increase by 160%. The distance over which the wind speed grows to 95% of the maximum wind speed shows large variations with maximum above 170 km and a mean of 67 km. The impact of the atmospheric boundary layer stability on horizontal wind speed gradients is investigated using additional information on air and sea temperature differences. The absolute SAR-derived wind speed increase offshore is usually higher in unstable situations and the respective adjustment distance is shorter. Furthermore, we have found atypical cases with a wind speed decrease offshore to be often connected to stable atmospheric conditions. A particular low-level jet (LLJ) situation is analysed in more detail using vertical wind speed profiles from a wind LIDAR system.

Influence of the atmospheric boundary layer stability on aerial spraying studied by computational fluid dynamics

Atmospheric stability can significantly influence the spray drift in aerial applications; however, to date its effects remain unclear. In this study, a large spatiotemporal aerial application simulation model was constructed using different atmospheric boundary layer (ABL) stabilities. Three sets of ABL stability conditions were considered: unstable, stable, and neutral. Velocity, temperature, turbulence kinetic energy, and turbulence dissipation rate were set in detail as boundary conditions. The simulation results indicated that, using a simulation of the typical fixed-wing agricultural aircraft operating at typical altitudes and speeds, the upwind vortex decays more slowly than the downwind vortex, while the movement of the downwind vortex is also faster. The strength of the vortex was found to influence the droplet concentration. Droplets dispersed more quickly under unstable conditions probably because of the turbulent kinetic energy were greater. Droplets under stable conditions moved much rapidly downwind but drifted at lower altitudes than under unstable conditions. The diameter of most of the drift spray droplets was <100 μm. The simulation results indicated that off-target deposition in the stable case was greater than in the unstable case by nearly 300% around at downwind distances of 100 m, 180 m, 700 m, and ∼200% at around 220 m and 550 m. Therefore, unstable atmospheric conditions, which are most likely to occur from 06:00 and 19:00 during a day appear to be a better choice for reducing drift losses. The simulation results are expected to help improve the comprehensive understanding of aerial application drift and to assist in choosing appropriate times and conditions to perform such operations. • Aerial spraying of pesticides is studied considering atmospheric boundary layer. • Vorticity field, droplet movement at various atmospheric stabilities are simulated. • Results show vortex shape and decay rate are affected by atmospheric stabilities. • Spraying operations in unstable weather conditions enable wide distribution. • Spraying operations in stable conditions result in more off-target deposition.

Wall-function-based weak imposition of Dirichlet boundary condition for stratified turbulent flows

Wall-function-based weak imposition of Dirichlet boundary condition (WFWD) has seen success in maintaining numerical accuracy with reduced near-wall resolution for modeling wall-bounded turbulent flows. In this work, we extend the formulation of WFWD to stably stratified flows. The performance of the extended formulation is validated with two canonical numerical experiments, namely stratified turbulent channel flow and stable atmospheric boundary layer, demonstrating its effectiveness and potential in modeling wall-bounded stratified turbulent flows. Comparisons are made against results of the original formulation of weak imposition of Dirichlet boundary condition (WD), as well as direct numerical or large-eddy simulations whenever available. Our results show that WFWD with a smooth wall function offers improved accuracy over its WD counterpart in predicting one-point statistics of the turbulent channel flow at various degrees of stratification. Furthermore, on account of adopting a rough wall function WFWD successfully predicts the occurrence of super-geostrophic jet as well as statistics that are in good agreement with highly-resolved large-eddy simulations. Our findings suggest that formulating the weak imposition of Dirichlet boundary condition based on wall functions could mitigate shortcomings of WD when factors like roughness play a non-negligible role.

Baroclinicity in stable atmospheric boundary layers: Characterizing turbulence structures and collapsing wind profiles via reduced models and large‐eddy simulations

AbstractBaroclinicity is a common, while often overlooked, phenomenon in the atmospheric boundary layer (ABL) that significantly impacts mean wind and turbulence structures. It adds another layer of complexity to the much‐studied stable barotropic ABLs by modulating the pressure gradient in height. Despite the prevalence of baroclinic and stable conditions in nature, our knowledge of their interacting effects on stratified ABL features is limited. The article aims to bridge this knowledge gap by systematically varying baroclinicity and stability using the large‐eddy simulation (LES) technique. The results of 15 conducted LESs indicate that baroclinicity alters the Ekman spiral shape and the low‐level jet's height in stable ABLs. Friction velocity, Obukhov length, shear production and the ABL height are highly influenced by baroclinicity in weakly stable ABLs, whereas they converge to a constant asymptote as the stability increases, independent of the baroclinicity regime. This is attributed to the strong turbulence destruction in very stable ABLs that decouples the surface from higher elevations where the baroclinicity effect is more significant. A reduced model for baroclinic wind profiles is developed and an analytical estimation of that for weakly baroclinic regimes is tested against LES results. Two rescaling methods in the inner and outer layers of stable baroclinic ABLs are used in a novel way to non‐dimensionalize the wind profiles. The suggested approaches reasonably collapse baroclinic/barotropic stable wind profiles in all considered LES cases. This study's findings elucidate the underlying physics of baroclinic stable ABLs and are useful for characterizing the wind profiles in weather/climate models, field measurements, and various industrial applications.

Emergence of optimal disturbances in a stratified turbulent shear flow under the stochastic forcing

Large-scale inclined organized structures in stably stratified turbulent shear flows were revealed in the numerical simulation and indirectly confirmed by the field measurements in the stable atmospheric boundary layer. Spatial scales and forms of these structures coincide with those of the optimal disturbances of a simplified linear model. In this paper, we clarify the relation between the organized structures and the optimal disturbances, analyzing a time series of turbulent fields obtained by the RANS model with eddy viscosity/diffusivity and stochastic forcing generating the small-scale turbulence.

Changes in atmospheric parameters due to annular solar eclipse of June 21, 2020, over India

In the present study, various solar and atmospheric parameters, namely solar radiation, surface ozone, relative humidity, air temperature, and wind speed, have been studied first time for the annular solar eclipse of June 21, 2020, at seven Indian stations simultaneously. All the seven different stations are selected along the solar eclipse path having the maximum eclipse magnitude of 92% and above. The various atmospheric parameters have shown the change in behavior during the solar eclipse duration. The incoming solar radiation has a maximum 95.97% decrease at Ludhiana at the time of maximum obscuration compared to the previous day. The surface ozone concentration has shown a decrease for all the seven stations during the maximum obscuration period. A maximum of 9.25% decrease in surface temperature has been observed nearly after 30 min of the time of maximum obscuration of the eclipse. Relative humidity started increasing at all the stations and showed an inverse trend from temperature. The wind speed was found to suppress during the maximum solar eclipse which may be attributed to stabilization of atmospheric boundary layer due to cooling.

On the u☆-U Relationship in the Stable Atmospheric Boundary Layer over Arctic Sea Ice

A relationship between the friction velocity u☆ and mean wind speed U in a stable atmospheric boundary layer (ABL) over Arctic sea ice was considered. To that aim, the observations collected during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment were used. The observations showed the so-called “hockey-stick” shape of the u☆−U relationship, which consists of a slow increase of u☆ with increasing wind speed for U&lt;Utr and a more rapid almost linear increase of u☆ for U&gt;Utr, where Utr is the wind speed of transition between the two regimes. Such a relationship is most pronounced at the highest observational levels, namely at 9 and 14 m, and is also sharper when the air-surface temperature difference exceeds its average values for stable conditions. It is shown that the Monin–Obukhov similarity theory (MOST) reproduces the observed u☆−U relationship rather well. This suggests that at least for the SHEBA dataset, there is no contradiction between MOST and the “hockey-stick” shape of the u☆−U relationship. However, the SHEBA data, as well as the single-column simulations show that for cases with strong stability, u☆ significantly decreases with height due to the shallowness of the ABL. It was shown that when u☆ was assumed independent of height, the value of the normalized drag coefficient, i.e., of the so-called stability correction function for momentum, calculated using observations at a certain level, can be significantly underestimated. To overcome this, the decrease of u☆ with height was taken into account in the framework of MOST using local scaling instead of the scaling with surface fluxes. Using such an extended MOST brought the estimates of the normalized drag coefficient closer to the Businger–Dyer relation.

Wind-Tunnel Simulation of Approximately Horizontally Homogeneous Stable Atmospheric Boundary Layers

Two cases of an overlying inversion imposed on a stable boundary layer are investigated, extending the work of Hancock and Hayden (Boundary-Layer Meteorol 168:29–57, 2018; 175:93–112, 2020). Vertical profiles of Reynolds stresses and heat flux show closely horizontally homogeneous behaviour over a streamwise fetch of more than eight boundary-layer heights. However, profiles of mean temperature and velocity show closely horizontally homogeneous behaviour only in the top two-thirds of the boundary layer. In the lower one-third the temperature decreases with fetch, directly as a consequence of heat transfer to the surface. A weaker effect is seen in the mean velocity profiles, curiously, such that the gradient Richardson number is invariant with fetch, while various other quantities are not. Stability leads to a ‘blocking’ of vertical influence. Inferred aerodynamic and thermal roughness lengths increase with fetch, while the former is constant in the neutral case, as expected. Favourable validation comparisons are made against two sets of local-scaling systems over the full depth of the boundary layer. Close concurrence is seen for all stable cases for z/L < 0.2, where z and L are the vertical height and local Obukhov length, respectively, and over most of the layer for some quantities.