On the relationship of aeolian relief, microrelief and wind direction with the concentration of dust aerosol in the near-surface layer

2021 ◽  
Author(s):  
Elena Malinovskaya ◽  
Otto Chkhetiani ◽  
Leonid Maksimenkov
Keyword(s):  
Wind Direction ◽  
Field Measurements ◽  
Submicron Particles ◽  
Russian Science ◽  
Near Surface ◽  
Knock Out ◽  
Wind Speeds ◽  
Aerosol Generation ◽  
Windward Slope ◽  
Slope Line

<p>Saltations, secondary knock-out of particles, and their rolling over the surface in the abrasion process are the main source of micron- and submicron-sized particles near the surface [1]. Zones with different aerosol generation rates and wiping dynamics emerge around growing aeolian structures [3,4]. On the leeward slope, larger particles remain in the embedding zone and abrasion is less active. On the windward slope, fractions of smaller size accumulate in the zone of cascade capture of layers by wind [2], and abrasion is predominant.</p><p> </p><p>The occurrence of aeolian forms varies in time depending on their height. Three areas are considered: 1-3 m, 1-3 cm, <1 cm. The effect of changes in wind direction at intervals of a few hours changes the length of zones near aeolian structures. Thus, the cascade trapping zone expands and the accumulation zone narrows. Aeolian microstructures on the surface of the windward slope decrease the length of the cascade capture zone, leaving structures with a height > 1 cm almost unchanged.</p><p> </p><p>We consider a sample of data from summer field measurements obtained in the evening with close values of air temperature (30-32°C) and wind speeds (6.1-6.5 m/s). Observations were made on a perennial patch of unfixed sands about 1.5 km long and 200-300 m wide at 5 km to the west of Naryn Khuduk settlement (Kalmykia, 2010-2020). The lines of dune ridges for this area extend approximately in the latitudinal direction.</p><p> </p><p>Based on the empirical functions of aerosol size and mass distribution, the classification related to the wind direction in relation to the line of windward and leeward slopes connection was obtained. When the wind direction changes from frontal to tangential along the slopes, mass concentrations of coarse aerosol fraction increase. This can be related to the processes of chipping for newly involved large particles from the layers of the leeward slope setting zone. The phenomenon is also illustrated by the observed emergence on the surface of a ripple with a ridge spacing of 10-30 cm during the next day of a micro-ridge with a period of 1-2 cm. For the windward slope line change model [5], it was obtained that the fraction of detached particles decreases with the growth of new structures. The presence of aeolian ripples [6] and larger particles generally reduces the fraction of particles moving in the wind flow.  There is weakening of wiping intensity at collision and reduction of concentration of submicron particles as a result, as compared to the case of absence of developed microrelief. The type of aerosol distribution function is influenced by the size of the embedding and cascade trapping zones and the composition of the layer of particles involved in collisions and displacements near the surface.</p><p>The study was supported by the Russian Science Foundation project 20-17-00214.</p><p> </p><p>1.Houser C.A., Nickling W.G. Sedimentology. 48(2). 255,. (2001)</p><p>2.Chepil W.S. Soil Science  60(4) 305.(1945)</p><p>3.Anderson R. Sedimentology 34, 943 (1987).</p><p>4.Hoyle R., Woods A. Phys. Rev. E 56, 6861 (1997).</p><p>5.Malinovskaya E.A. Izvestiya. Atmospheric and Oceanic Physics 55(2) 218 (2019)</p><p>6. Malinovskaya E. et al. EGU2019-3693-1 (2019)</p><p> </p>

scholarly journals A Numerical Study on the Impact of Building Dimensions on Airflow Patterns and Bed Morphology around Buildings at the Beach

2021 ◽  
Vol 10 (1) ◽  
pp. 13
Author(s):  
Paran Pourteimouri ◽  
Geert H. P. Campmans ◽  
Kathelijne M. Wijnberg ◽  
Suzanne J. M. H. Hulscher
Keyword(s):  
Wind Direction ◽  
Numerical Study ◽  
Field Measurements ◽  
Surface Velocity ◽  
Erosion And Deposition ◽  
Transport Pathways ◽  
Near Surface ◽  
Deposition Patterns ◽  
Numerical Predictions ◽  
The Impact

The attractiveness of beaches to people has led, in many places, to the construction of buildings at the beach–dune interface. Buildings change the local airflow patterns which, in turn, alter the sediment transport pathways and magnitudes. This induces erosion and deposition patterns around the structures. In this study, a numerical model is developed using the open-source computational fluid dynamics solver OpenFOAM. First, the model is used to predict the airflow patterns around a single rectangular building. The model predictions are validated with wind-tunnel data, which show good agreements. Second, a reference beach building is introduced and then the building dimensions are increased in length, width and height, each up to three times the reference building dimension. The impact of each dimensional extent on the near-surface airflow patterns is investigated. The results show that the near-surface airflow patterns are least dependent on the length of the building in the wind direction and they depend most on the width of the building perpendicular to the wind direction. Third, the convergence of the third-order horizontal near-surface velocity field is calculated to interpret the impact of changes in airflow patterns on potential erosion and deposition patterns around the building. The numerical predictions are compared with the observed erosion and sedimentation patterns around scale models in the field. The comparisons show satisfactory agreements between numerical results and field measurements.

scholarly journals Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

2020 ◽  
Vol 13 (6) ◽  
pp. 3487-3506
Author(s):  
Sebastian Landwehr ◽  
Iris Thurnherr ◽  
Nicolas Cassar ◽  
Martin Gysel-Beer ◽  
Julia Schmale
Keyword(s):  
Wind Speed ◽  
Computational Fluid Dynamic ◽  
Wind Direction ◽  
Fluid Dynamic ◽  
Reanalysis Data ◽  
Correction Factors ◽  
Flow Distortion ◽  
Near Surface ◽  
Wind Speeds ◽  
Relative Wind

Abstract. At sea, wind forcing is responsible for the formation and development of surface waves and represents an important source of near-surface turbulence. Therefore, processes related to near-surface turbulence and wave breaking, such as sea spray emission and air–sea gas exchange, are often parameterised with wind speed. Thus, shipborne wind speed measurements provide highly relevant observations. They can, however, be compromised by flow distortion due to the ship's structure and objects near the anemometer that modify the airflow, leading to a deflection of the apparent wind direction and positive or negative acceleration of the apparent wind speed. The resulting errors in the estimated true wind speed can be greatly magnified at low wind speeds. For some research ships, correction factors have been derived from computational fluid dynamic models or through direct comparison with wind speed measurements from buoys. These correction factors can, however, lose their validity due to changes in the structures near the anemometer and, thus, require frequent re-evaluation, which is costly in either computational power or ship time. Here, we evaluate if global atmospheric reanalysis data can be used to quantify the flow distortion bias in shipborne wind speed measurements. The method is tested on data from the Antarctic Circumnavigation Expedition onboard the R/V Akademik Tryoshnikov, which are compared to ERA-5 reanalysis wind speeds. We find that, depending on the relative wind direction, the relative wind speed and direction measurements are biased by −37 % to +22 % and -17∘ to +11∘ respectively. The resulting error in the true wind speed is +11.5 % on average but ranges from −4 % to +41 % (5th and 95th percentile). After applying the bias correction, the uncertainty in the true wind speed is reduced to ±5 % and depends mainly on the average accuracy of the ERA-5 data over the period of the experiment. The obvious drawback of this approach is the potential intrusion of model biases in the correction factors. We show that this problem can be somewhat mitigated when the error propagation in the true wind correction is accounted for and used to weight the observations. We discuss the potential caveats and limitations of this approach and conclude that it can be used to quantify flow distortion bias for ships that operate on a global scale. The method can also be valuable to verify computational fluid dynamic studies of airflow distortion on research vessels.

scholarly journals Field Measurements of Hanging Flight Aerodynamics in the Kestrel Falco Tinnunculus

1991 ◽  
Vol 155 (1) ◽  
pp. 519-530
Author(s):  
JOHN VIDELER ◽  
ALEX GROENEWOLD
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Wind Profile ◽  
Field Measurements ◽  
Vertical Wind ◽  
Horizontal Direction ◽  
Falco Tinnunculus ◽  
Windward Slope ◽  
Sea Dike

Hunting kestrels were observed to hang, almost without wing-flapping, in fixed positions over a sea dike. The height and position with respect to the dike profile, the wind direction and velocity and the percentage of hunting time without wing beating were recorded in 429 cases. The vertical wind angle, θ, the wind speed and its horizontal direction were measured at 13 heights up to 8.8m above the windward slope, the top and the leeward slope of the dike under various wind conditions in 225 cases. These wind profile measurements were used to estimate 6 and wind speed near the hanging birds. Kestrels hanging more than 90% of the hunting time preferred a position 6.5±1.5m (S.D.) over the windward slope with sea winds blowing at 8.7±1.5ms−1 (S.D.) perpendicular (±30°) to the longitudinal dike axis. For these birds angle θ was approximately 6–7°. These angles are larger than expected from aerodynamic models and windtunnel measurements. The minimum gliding angle for a kestrel under steady conditions is estimated to be 5°. Hanging kestrels save two-thirds of the energy used during normal windhovering but have to spend 1.6 times more time to catch the same number of voles.

scholarly journals Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

2019 ◽  
Author(s):  
Sebastian Landwehr ◽  
Iris Thurnherr ◽  
Nicolas Cassar ◽  
Martin Gysel-Beer ◽  
Julia Schmale
Keyword(s):  
Wind Speed ◽  
Computational Fluid Dynamic ◽  
Wind Direction ◽  
Fluid Dynamic ◽  
Correction Factors ◽  
Flow Distortion ◽  
Near Surface ◽  
Wind Speeds ◽  
Surface Turbulence ◽  
Relative Wind

Abstract. At sea, wind forcing is responsible for the formation and development of surface waves and represents an important source of near surface turbulence. Therefore, processes related to near surface turbulence and wave breaking, such as sea spray emission and air-sea gas exchange are often parametrised with wind speed. Shipborne wind speed measurements thus provide highly relevant observations. They can, however, be compromised by flow distortion due to the ship's structure and objects nearby the anemometer that modify the airflow, leading to a deflection of the apparent wind direction and positive or negative acceleration of the apparent wind speed. The resulting errors in the estimated true wind speed can be greatly magnified at low wind speeds. For some research ships, correction factors have been derived from computational fluid dynamic models or through direct comparison with wind speed measurements from buoys. These correction factors can, however, loose their validity due to changes of the structures nearby the anemometer and thus require frequent re-evaluation, which is costly in either computational power or ship time. Here we evaluate if global weather forecast model data can be used to quantify the flow distortion bias in shipborne wind speed measurements. The method is tested on data from the Antarctic Circumnavigation Expedition (ACE) on board the R/V Akademik Tryoshnikov, which are compared with ERA-5 reanalysis wind speeds. We find that, depending on the relative wind direction, the relative wind speed and direction measurements are biased by −37 % to +20 % and −13° to +15°, respectively. The resulting error in the true wind speed is +11 % on average but ranges from −5 % to +40 % (5th and 95th percentile). After applying the bias correction, the uncertainty in the true wind speed is reduced to 5 % and depends mainly on the average accuracy of the ERA-5 data over the period of the experiment. The obvious drawback of this approach is the potential intrusion of model bias in the correction factors. We show that this problem can be somewhat mediated when the error propagation in the true wind correction is accounted for and used to weight the observations. We discuss the potential caveats and limitations of this approach and conclude that it can be used to quantify flow distortion bias for ships that operate on a global scale. The method can also be valuable to verify Computational Fluid Dynamic studies of airflow distortion on research vessels.

scholarly journals Projected Changes in European and North Atlantic Seasonal Wind Climate Derived from CMIP5 Simulations

2019 ◽  
Vol 32 (19) ◽  
pp. 6467-6490 ◽  
Author(s):  
Kimmo Ruosteenoja ◽  
Timo Vihma ◽  
Ari Venäläinen
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Global Climate ◽  
Arctic Sea Ice ◽  
Global Climate Models ◽  
Near Surface ◽  
Wind Speeds ◽  
The North ◽  
Seasonal Wind ◽  
Projected Changes

Abstract Future changes in geostrophic winds over Europe and the North Atlantic region were studied utilizing output data from 21 CMIP5 global climate models (GCMs). Changes in temporal means, extremes, and the joint distribution of speed and direction were considered. In concordance with previous research, the time mean and extreme scalar wind speeds do not change pronouncedly in response to the projected climate change; some degree of weakening occurs in the majority of the domain. Nevertheless, substantial changes in high wind speeds are identified when studying the geostrophic winds from different directions separately. In particular, in northern Europe in autumn and in parts of northwestern Europe in winter, the frequency of strong westerly winds is projected to increase by up to 50%. Concurrently, easterly winds become less common. In addition, we evaluated the potential of the GCMs to simulate changes in the near-surface true wind speeds. In ocean areas, changes in the true and geostrophic winds are mainly consistent and the emerging differences can be explained (e.g., by the retreat of Arctic sea ice). Conversely, in several GCMs the continental wind speed response proved to be predominantly determined by fairly arbitrary changes in the surface properties rather than by changes in the atmospheric circulation. Accordingly, true wind projections derived directly from the model output should be treated with caution since they do not necessarily reflect the actual atmospheric response to global warming.

scholarly journals Modulation of urban atmospheric electric field measurements with the wind direction in Lisbon (Portugal)

2015 ◽  
Vol 646 ◽  
pp. 012013 ◽  
Author(s):  
H G Silva ◽  
J C Matthews ◽  
R Conceição ◽  
M D Wright ◽  
S N Pereira ◽  
...  
Keyword(s):  
Electric Field ◽  
Wind Direction ◽  
Field Measurements ◽  
Atmospheric Electric Field ◽  
Electric Field Measurements

Field evidence of resuspension in a mine tailings pond

2001 ◽  
Vol 38 (4) ◽  
pp. 796-808 ◽  
Author(s):  
Celestina Adu-Wusu ◽  
Ernest K Yanful ◽  
Mohammed H Mian
Keyword(s):  
Shear Stress ◽  
Mine Tailings ◽  
Critical Shear Stress ◽  
Field Measurements ◽  
Shear Stresses ◽  
Wind Speeds ◽  
Tailings Pond ◽  
Field Evidence ◽  
Water Cover ◽  
Solubility Of Oxygen

Flooding of tailings under shallow water covers is an effective method of decommissioning potentially acid generating mine tailings. The low diffusivity and solubility of oxygen in water are attractive features of this technology. However, wind-induced waves can resuspend flooded tailings and expose them to greater contact with dissolved oxygen, thereby increasing the potential for oxidation and acid generation. Field measurements of wind activity and waves under different water cover depths and associated resuspension for a mine tailings pond in Ontario are presented and discussed. The results show that wind speeds greater than 8 m/s above water covers that are shallower than 1 m create waves of height greater than 10 cm and bottom shear stresses greater than 0.2 Pa. Under these conditions the critical shear stress of the mine tailings was exceeded, resulting in erosion and subsequent resuspension.Key words: mine tailings, water cover, wind-induced waves, resuspension, wind speed, shear stress.

scholarly journals Local Characteristics of the Nocturnal Boundary Layer in Response to External Pressure Forcing

2017 ◽  
Vol 56 (11) ◽  
pp. 3035-3047 ◽  
Author(s):  
Steven J. A. van der Linden ◽  
Peter Baas ◽  
J. Antoon van Hooft ◽  
Ivo G. S. van Hooijdonk ◽  
Fred C. Bosveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Stable Boundary Layer ◽  
Dynamical Behavior ◽  
Geostrophic Wind ◽  
External Pressure ◽  
Near Surface ◽  
Stable Boundary ◽  
Wind Speeds ◽  
Turbulent Characteristics

AbstractGeostrophic wind speed data, derived from pressure observations, are used in combination with tower measurements to investigate the nocturnal stable boundary layer at Cabauw, the Netherlands. Since the geostrophic wind speed is not directly influenced by local nocturnal stability, it may be regarded as an external forcing parameter of the nocturnal stable boundary layer. This is in contrast to local parameters such as in situ wind speed, the Monin–Obukhov stability parameter (z/L), or the local Richardson number. To characterize the stable boundary layer, ensemble averages of clear-sky nights with similar geostrophic wind speeds are formed. In this manner, the mean dynamical behavior of near-surface turbulent characteristics and composite profiles of wind and temperature are systematically investigated. The classification is found to result in a gradual ordering of the diagnosed variables in terms of the geostrophic wind speed. In an ensemble sense the transition from the weakly stable to very stable boundary layer is more gradual than expected. Interestingly, for very weak geostrophic winds, turbulent activity is found to be negligibly small while the resulting boundary cooling stays finite. Realistic numerical simulations for those cases should therefore have a comprehensive description of other thermodynamic processes such as soil heat conduction and radiative transfer.

scholarly journals Field Measurements of Surface and Near-Surface Turbulence in the Presence of Breaking Waves

2015 ◽  
Vol 45 (4) ◽  
pp. 943-965 ◽  
Author(s):  
Peter Sutherland ◽  
W. Kendall Melville
Keyword(s):  
Field Experiments ◽  
North Pacific Ocean ◽  
Large Fraction ◽  
Field Measurements ◽  
Breaking Waves ◽  
Sea Surface ◽  
Near Surface ◽  
Wave Energy Dissipation ◽  
Eddy Simulation ◽  
The North

AbstractWave breaking removes energy from the surface wave field and injects it into the upper ocean, where it is dissipated by viscosity. This paper presents an investigation of turbulent kinetic energy (TKE) dissipation beneath breaking waves. Wind, wave, and turbulence data were collected in the North Pacific Ocean aboard R/P FLIP, during the ONR-sponsored High Resolution Air-Sea Interaction (HiRes) and Radiance in a Dynamic Ocean (RaDyO) experiments. A new method for measuring TKE dissipation at the sea surface was combined with subsurface measurements to allow estimation of TKE dissipation over the entire wave-affected surface layer. Near the surface, dissipation decayed with depth as z−1, and below approximately one significant wave height, it decayed more quickly, approaching z−2. High levels of TKE dissipation very near the sea surface were consistent with the large fraction of wave energy dissipation attributed to non-air-entraining microbreakers. Comparison of measured profiles with large-eddy simulation results in the literature suggests that dissipation is concentrated closer to the surface than previously expected, largely because the simulations did not resolve microbreaking. Total integrated dissipation in the water column agreed well with dissipation by breaking for young waves, (where cm is the mean wave frequency and is the atmospheric friction velocity), implying that breaking was the dominant source of turbulence in those conditions. The results of these extensive measurements of near-surface dissipation over three field experiments are discussed in the context of observations and ocean boundary layer modeling efforts by other groups.

scholarly journals Bayesian Model Averaging for Wind Speed Ensemble Forecasts Using Wind Speed and Direction

2017 ◽  
Vol 32 (6) ◽  
pp. 2217-2227 ◽  
Author(s):  
Siri Sofie Eide ◽  
John Bjørnar Bremnes ◽  
Ingelin Steinsland
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Bayesian Model Averaging ◽  
Weather Prediction ◽  
Model Averaging ◽  
Strong Wind ◽  
Ensemble Forecasts ◽  
Wind Speeds ◽  
Low Wind Speeds ◽  
The One

Abstract In this paper, probabilistic wind speed forecasts are constructed based on ensemble numerical weather prediction (NWP) forecasts for both wind speed and wind direction. Including other NWP variables in addition to the one subject to forecasting is common for statistical calibration of deterministic forecasts. However, this practice is rarely seen for ensemble forecasts, probably because of a lack of methods. A Bayesian modeling approach (BMA) is adopted, and a flexible model class based on splines is introduced for the mean model. The spline model allows both wind speed and wind direction to be included nonlinearly. The proposed methodology is tested for forecasting hourly maximum 10-min wind speeds based on ensemble forecasts from the European Centre for Medium-Range Weather Forecasts at 204 locations in Norway for lead times from +12 to +108 h. An improvement in the continuous ranked probability score is seen for approximately 85% of the locations using the proposed method compared to standard BMA based on only wind speed forecasts. For moderate-to-strong wind the improvement is substantial, while for low wind speeds there is generally less or no improvement. On average, the improvement is 5%. The proposed methodology can be extended to include more NWP variables in the calibration and can also be applied to other variables.

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