Search

Using high-frequency onshore wind data from four different heights of a coastal tower, the variations in gust factor with turbulence intensity, height and wind speed were studied under typhoon conditions. The gust factor increases with increasing turbulence intensity and, most often, can be described by a linear relationship with the turbulence intensity. The gust factor decreases with height and is relatively small compared with those presented in the national codes and other studies. A value of 2.5 is acceptable for the peak factor, which is close to the recommended value of the national code in China. The gust factor increases with increasing wind speed and is also affected by the wind direction. The gust factor has a value to that of previously published results when the wind flows roughly perpendicular to the shoreline, and has a smaller value when the wind flows roughly parallel to the shoreline. The phenomenon is caused by the confinement of shoreline on the sea wave development. Sea waves tend to propagate normal to the shoreline because of the refraction effect. As a result, a shorter roughness length exists in the parallel direction to the shoreline. It can be further explained by the weakness in the momentum flux exchange between the air and sea based on the wave form drag theory when the wind flows parallel to the shoreline.

Understanding the aerodynamic characteristics of landfalling typhoons is of great importance for both wind engineering and meteorology. This study comparatively investigated the near‐surface wind profiles and aerodynamic parameters over coastland and coastal sea areas using typhoon observational data collected by Doppler wind lidars and wind tower anemometers during the passage of 15 typhoons that made landfall over China during 2009–2020. Specifically, the three surface aerodynamic parameters of roughness length, friction velocity, and drag coefficient (Cd) were obtained using the logarithmic law wind profile method. Results showed that the near‐surface wind profiles became much closer to the power law wind profile with increase in wind speed. The values of roughness length and friction velocity over the coastal sea were found to exceed those over coastland areas when the 10‐m wind speed (U(10)) was larger than 18 m s−1. The critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1. There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the sea, which has never been reported in previous observational studies. Finally, a formula for Cd was proposed to describe the variation in Cd with U(10) under the condition of onshore wind over land, which is expected to be applied in the typhoon surface layer scheme to improve numerical simulation of landfalling typhoons. Plain Language Summary: Typhoons are one of the most destructive natural disasters that cause severe economic losses and human casualties in many parts of the world. Understanding the typhoon wind field is important for designing high‐rise buildings and improving weather forecast. In order to understand how the near‐surface wind field change in coastal regions, we measure it using specialized observation instruments during the passage of 15 typhoons that made landfall over China and analyze the results of the measurements. We find that the aerodynamic characteristics of typhoons over coastland are very different from those over the coastal sea. A specialized surface aerodynamic parameter called drag coefficient, which represents the momentum transport efficiency on the sea/land surface, is found to reach its maximum value when the 10‐m wind speed is 24 m s−1 over the coastal sea. Interestingly, two peaks are observed in the plot of drag coefficient as a function of 10‐m wind speed under the condition of onshore wind over the coastal sea, which has not been reported before in any other related studies. Further development of the typhoon numerical models should take these results into account. Key Points: Values of roughness length and friction velocity over the coastal sea were found to exceed those over the coastland for U(10) > 18 m s−1Critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the coastal sea [ABSTRACT FROM AUTHOR]

The Empty Quarter Desert, one of Earth's major dust sources, frequently experiences dust storms due to wind erosion. Despite its significance as a primary dust source on a global scale, in‐situ observations from this region had not been reported until very recently. In summer 2022, the WInd‐blown Sand Experiment (WISE) Phase‐1 was initiated in the Empty Quarter Desert of the United Arab Emirates, and continued until 7 February 2023. Utilizing a diverse array of instruments, we measured winds, temperature, humidity, radiation fluxes, saltation, and the physical and optical properties of dust aerosols, atmospheric electric fields, and soil characteristics. A total of 38 distinct sand‐saltation events were recorded from September 2022 to February 2023, with activity peaking between 13:00 and 14:00 local time. Key findings include the identification of dominant wind patterns, and the measurement of the average aerodynamic roughness length (z0) at 0.8 ± 0.6 mm, and the thermal roughness length (zh) at 0.3 ± 0.5 mm—the first estimation of zh for this area. In‐situ observations revealed that dust particle concentrations near the surface increased 1.7‐fold on days with saltation compared to days without it. Moreover, we determined a wind‐speed threshold for initiating saltation at 7.70 m s−1. This comprehensive data set significantly advances our understanding of atmospheric‐soil interactions and sand movement dynamics, providing invaluable insights for ongoing research into desert environments and the global dust cycle. Plain Language Summary: The Empty Quarter Desert, one of the Earth's major dust sources, frequently experiences dust storms due to wind erosion. Despite its importance as a main dust source on a global scale, no in‐situ observations from this region have been reported until very recently. In the summer of 2022, the WInd‐blown Sand Experiment (WISE) Phase‐1 provided crucial data on the arid environment of the Empty Quarter Desert in the United Arab Emirates. Lasting until February 2023, this experiment focused on quantifying environmental and soil characteristics through an array of measurements, including wind direction and speed, temperature, humidity, radiation fluxes, and dust particle concentrations. The study revealed dominant wind patterns, quantified the aerodynamic and thermal roughness of the desert soil, and recorded 38 distinct sand movement events, noting a peak in activity during early afternoon hours. This research is significant for its detailed analysis of particle concentration changes during these events and its establishment of a specific wind speed threshold for sand movement in this region. These findings are invaluable for researchers studying desert environments, particularly in terms of understanding atmospheric‐soil interactions and the dynamics of sand movement. Key Points: First‐of‐its kind experiment in the Empty Quarter Desert to characterize environmental dynamicsThe first estimation of the thermal roughness length (zh) for this desert and is found to be 0.3 mmThe derived wind‐speed threshold for saltation at the Empty Quarter Desert is 7.70 m s−1 [ABSTRACT FROM AUTHOR]

Exact knowledge of wind energy potential is a fundamental issue in wind energy utilization. The vertical changes in wind speeds, that is, the wind profile, have a predominant impact on the wind energy available at a location because the kinetic energy of moving air is proportional to the square of the wind speed. Roughness describes the resistance of a 3D surface to moving air. The exponent α of the power law of Hellmann and the roughness length (z0) are two parameters that describe the effects of the roughness of the surface on the wind profile. They can be used for the vertical extrapolation of wind speeds. The exponent α can be determined using multiple height level wind speed measurement data, whereas a reliable technique for the calculation of the roughness length requires detailed knowledge of the 3D geometry of the measurement site. In the present study, the exponent α was calculated based on SODAR wind speed measurements, while (z0) was determined using a combination of GIS and UAS-based aerial survey methods. Wind speeds measured at 50 m were extrapolated for height levels of 80, 90, 100, 110, and 120 m using dynamic power law exponent values. Wind power was determined using the power law (method V1), roughness length (method V2), frequency distribution (method W-RF), and gamma distribution (method W-G), and Windographer software was compared to the values calculated from the empirical (measured) wind speeds. A comparative statistical analysis of the datasets of the power law and roughness length methods on monthly/diurnal, annual/diurnal, and month/direction contexts showed no significant differences at all height levels. Differences can be detected in the distribution of the signs of the differences at heights of 80 and 120 m for the entire dataset. Underestimation was dominant with a significant frequency (over 70 %) in the case of both methods and heights. There were no significant differences between the wind power estimations provided by the different methods, and all the methods involved in the study underestimated the wind speeds and wind energy potential for each height level. Methods V1 and V2 can be used alternatively, depending on the input data available for analysis. The major advantage of method V2 is that it provides the same accuracy as V1, which requires a UAS-based aerial survey at the beginning, but continuous wind measurements must be performed at a lower height only. This means that there is no need for a high measurement tower, which makes the measurements simpler, more cost-effective, and causes much less disturbance to the environment. Another important advantage of the methods presented here is that they use a dynamic approach of power law exponent values that provide a more realistic estimation of wind speed and energy on a diurnal scale.

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The Empty Quarter Desert, one of Earth's major dust sources, frequently experiences dust storms due to wind erosion. Despite its significance as a primary dust source on a global scale, in‐situ observations from this region had not been reported until very recently. In summer 2022, the WInd‐blown Sand Experiment (WISE) Phase‐1 was initiated in the Empty Quarter Desert of the United Arab Emirates, and continued until 7 February 2023. Utilizing a diverse array of instruments, we measured winds, temperature, humidity, radiation fluxes, saltation, and the physical and optical properties of dust aerosols, atmospheric electric fields, and soil characteristics. A total of 38 distinct sand‐saltation events were recorded from September 2022 to February 2023, with activity peaking between 13:00 and 14:00 local time. Key findings include the identification of dominant wind patterns, and the measurement of the average aerodynamic roughness length (z0) at 0.8 ± 0.6 mm, and the thermal roughness length (zh) at 0.3 ± 0.5 mm—the first estimation of zh for this area. In‐situ observations revealed that dust particle concentrations near the surface increased 1.7‐fold on days with saltation compared to days without it. Moreover, we determined a wind‐speed threshold for initiating saltation at 7.70 m s−1. This comprehensive data set significantly advances our understanding of atmospheric‐soil interactions and sand movement dynamics, providing invaluable insights for ongoing research into desert environments and the global dust cycle.

Average empirical estimations of the surface air layer height in Moscow have been received by the data of long-term acoustic remote sensing of the atmosphere using the MODOS Doppler sodar (METEK, Germany). Based on the assumption that the average conditions are close to neutral stratification, this height, as the top of the quasi-linear section of the average long-term wind velocity profile in semilogarithmic coordinates, is 40–60 m. The wind rotation height, i.e., the height of intersection of day and night wind profiles, is 95 m per year on average. The roughness length in conditions of loosely packed but high urban development in the vicinity of Moscow State University in Moscow is 5 m. According to the criterion of the constant wind direction in the surface air layer, its height manifests itself in the monthly average wind direction profiles over the "dead zone" of the sodar (40 m) in approximately one out of three cases and usually amounts to 60 m (less often 80 or 100 m). In all other cases, it is apparently masked by the dead zone. According to this approach, the average height of the surface layer is probably a little less than 50 m, which is close to the estimate obtained from the logarithmic distribution of wind velocity with height in this layer. The daily variation of the surface air layer height is noted by the largest values in the afternoon (80–100 m in summer under conditions of prevailing unstable stratification and 60–80 m in winter) and the smallest ones (less than 40 m) in the late evening and at night in summer and from evening to noon in winter. [ABSTRACT FROM AUTHOR]

Wind-tunnel modeling of Atmospheric Boundary Layer flows has primarily consisted of simplified (purely uniform) upwind terrain conditions. This approach is easier to carry out but may not replicate the true wind characteristics of the site. This paper proposes a method to simulate nonuniform terrains in a wind-tunnel and investigates the wind characteristics produced by the method. The proposed method employs the local roughness zones where the given terrain is divided into sub-areas with an approximately uniform roughness length. Next, each sub-area is represented in the wind-tunnel with uniform roughness elements. However, the overall upwind fetch will be composed of roughness elements of various heights. To study the wind characteristics produced by the method, nine different real-world sites were simulated in the Boundary Layer Wind Tunnel at the University of Florida Natural Hazard Engineering Infrastructure Experimental Facility, using a self-configurable (automated) roughness element grid. Compared with the conventional equivalent uniform representation, similarities and differences in the longitudinal mean velocity, turbulence intensity, wind spectrum, and integral length scale profiles are reported and discussed. In particular, a significant difference was observed for the higher-order moments of the longitudinal velocity component, which indicates the need for further studies in wind loads under nonuniform terrains. [ABSTRACT FROM AUTHOR]

Based on morphological methods, MODIS satellite remote sensing data were used to establish a dataset of the local roughness length (Z0) of vegetation-covered surfaces in Guangdong Province. The local Z0 was used to update the mesoscale Weather Research and Forecasting (WRF) model in order to quantitatively evaluate its impact on the thermodynamic environment of vegetation-covered surfaces. The specific results are as follows: evergreen broad-leaved forests showed the largest average Z0 values at 1.27 m (spring), 1.15 m (summer), 1.03 m (autumn), and 1.15 m (winter); the average Z0 values of mixed forests ranged from 0.90 to 1.20 m; and those for cropland-covered surfaces ranged from 0.17 to 0.20 m. The Z0 values of individual vegetation coverage types all exhibited relatively high values in spring and low values in autumn, and the default Z0 corresponding to specific vegetation-covered surfaces was significantly underestimated in the WRF model. Modifying the default Z0 of surfaces underlying evergreen broad-leaved forests, mixed forests, and croplands in the model induced only relatively small changes (<1%) in their 2 m temperature, relative humidity, skin surface temperature, and the planetary boundary layer height. However, the average daily wind speed of surfaces covered by evergreen broad-leaved forests, mixed forests, and croplands was reduced by 0.48 m/s, 0.43 m/s, and 0.26 m/s, respectively, accounting for changes of 12.0%, 11.1%, and 6.5%, respectively. [ABSTRACT FROM AUTHOR]

This paper discusses how the incorporation of high-resolution ground coverage dataset ESA WorldCover into a wind flow field and wake simulation calculation, as well as the use of the coupled wake model for wind farm output simulation, can improve the accuracy of wind resource assessment using engineering examples. In the actual case of grid-connected wind farms in central China, SCADA wind speed data is reconstructed to the free flow wind speed in front of the wind turbine impeller using the transfer function of the nacelle, and the wind farm is modeled using OpenWind software, simulating the wind speed at the height of each wind turbine hub and each wind turbine output. The results show that when other initial data are consistent, using ESA's high-precision land cover dataset WorldCover 10 m to make roughness lengths which improves the wind farm output simulation accuracy by 8.91%, showing that it is worth trying to apply WorldCover 10 m to the wind farm simulation design. At the same time, this case is used to compare and analyze the application of the Eddy-Viscosity wake model and the two coupled wake models based on the Eddy-Viscosity wake model. The results show that the coupled wake model will have higher accuracy than the Deep Array Eddy Viscosity wake model and it is 1.24% more accurate than the Eddy Viscosity wake model, and the ASM Eddy Viscosity wake model is 5.21% more accurate than the Eddy Viscosity wake model. [ABSTRACT FROM AUTHOR]

In this work, we carried out roughness-resolved direct numerical simulations of cube-roughened turbulent channel flows to investigate the effects of aligned and staggered arrangements, element spacings, and element orientations on the statistics of rough-wall turbulence. The results show that the equivalent sandgrain roughness, Reynolds stresses and dispersive stresses are affected by element spacings and arrangements in different ways depending on the cube orientations. Placing the roughness elements in a staggered way in general increases the equivalent sandgrain roughness, unless when the element–element interaction is insignificant for the cube orientation with wakes of short length. As for the Reynolds normal stresses and the streamwise component of the dispersive stresses (both are normalized by the total friction velocity), placing the cube elements in a staggered way decreases their maximal values when compared with the aligned arrangements. As for the effects of element spacing on the equivalent sandgrain roughness and the maximums of the Reynolds normal stresses, similar trends are observed for different element orientations and arrangements when increasing the element spacing l/r (where r is the cube height) from 2.0 to 2.8. When further increasing the element spacing l/r from 2.8 to 3.5, however, different trends are observed for different element orientations. As for the dispersive stresses, greater maximal values of their streamwise components are observed for larger element spacing for all the considered cube-roughened surfaces. For the turbulence statistics in the wake of the cube element, certain similarities are observed for different element spacings. [ABSTRACT FROM AUTHOR]

Via analysis of velocity and stress fields from Reynolds-Averaged Navier–Stokes simulations over diverse complex terrains spanning several continents, in neutral conditions we find displaced areal-mean logarithmic wind speed profiles. The corresponding effective roughness length ( z 0,eff ), friction velocity ( u ∗ ,eff ), and displacement height ( d eff ) characterise the drag exerted by the terrain. Simulations and spectral analyses reveal that the terrain statistics—and consequently d eff , u ∗ ,eff and z 0,eff —can change significantly with flow direction, including flow in opposite directions. Previous studies over scaled or simulated fractal surfaces reported z 0,eff to depend on the standard deviation of terrain elevation ( σ h ), but over real terrains we find z 0,eff varies with standard deviation of terrain slopes ( σ Δ h / Δ x ). Terrain spectra show the dominant scales contributing to σ Δ h / Δ x vary from ∼ 1–10 km, with power-law behaviour over smaller scales corresponding to fractal terrain used in earlier works. The dependence of z 0,eff on σ Δ h / Δ x is consistent with fractal terrain having σ Δ h / Δ x ∝ σ h , as well as classic theory for individual hills. We obtain relationships for z 0,eff , d eff , and u ∗ ,eff in terms of σ Δ h / Δ x , finding that d eff acts as a characteristic length scale within z 0,eff . Considering flow in opposite directions, use of upslope statistics did not improve z 0,eff predictions; sheltering effects likely require more sophisticated treatment. Our findings impact practical applications and research, including micrometeorological flow, computational fluid dynamics, atmospheric model coupling, and mesoscale and climate modelling. We discuss limitations of the z 0,eff formulations developed herein, and provide recommendations for practical use. [ABSTRACT FROM AUTHOR]

Forced by observations from 1 June to 31 August 2014， which are provided by Naqu station of Plateau Climate and Environment in northern Qinghai-Xizang Plateau， CLM4.5 is used to evaluate the influence on simulated results of both radiation balance and exchange of water-heat after some surface parameters and parameterization schemes including LAI、 vegetation coverage and roughness length have changed.The reason for these changes are also discussed in this article.The results suggested that （1） Compared with the results produced by default scheme Z98， those of schemes named Z12 and B82 perform better in decreasing the positive bias of latent heat fluxes and negative bias of sensible heat fluxes.（2） aerodynamic roughness length calculated by revised Massman model and a method named “Chen” are respectively used to replace the default value， the outcomes produced by CLM approach the observations further.（3）With leaf area index increasing， sensible heat fluxes and reflected radiation and surface long-wave radiation decrease a lot， while latent heat fluxes are on the increase.（4）As the vegetation cover increases， latent fluxes decreases， while sensible heat fluxes and reflected radiation and surface long-wave radiation rise， meanwhile soil temperature and moisture also rise.The aim of this study is to provide a basis for future ambition to simulate the balance of ground surface water and heat over the whole Plateau.

Precipitation has a significant influence on the topsoil moisture and further impacts the land-atmospheric water and heat exchange process over the Yarlung Zangbo Grand Canyon region (YGC) where exhibits one of the highest frequencies of convective activity in China. The simulated performance of the Community Land Model version 5.0 (CLM5.0) on turbulent fluxes under seven roughness heights for heat transfer (Z0h) schemes at Motuo and Pailong stations over the YGC was evaluated. The results indicate that the CLM5.0 significantly overestimates the surface sensible heat flux (H) while the simulation performance of surface latent heat flux (LE) is better than H. By comparing and analyzing the simulation results, the Z0h schemes suitable for the YGC are selected optimally. The Zeng et al. (J. Hydrometeorol., 2012, 13, 1359–1370) scheme (Z12) is more suitable for the simulations of H, with the simulated RMSE of H at Motuo and Pailong stations on typical sunny days being only 21.63 and 15.13 W m−2, respectively, 81.51% and 76.96% lower than the original Z0h scheme of CLM5.0. The Garratt, J., R and Francey, R., J (Boundary. Layer. Meteorol., 1978, 15, 399–421) scheme (G78) is more suitable for simulating LE in the YGC. The simulated BIAS and RMSE of LE at Motuo station were 9.80% and 21.90% lower than that under the default scheme of CLM5.0 on typical cloudy days. In addition, except for the G78 and CLM5.0 default scheme, the Z0h under the other schemes showed obvious diurnal variation characteristics, and H was positively sensitive to Z0h, while LE was the opposite. Consequently, the optimal Z0h schemes are of great application value for further comparative analysis of the water and heat exchange process between the Grand Canyon land surface and the atmosphere, to better reveal the mechanism of land-atmosphere interactions in the YGC.

Comprehensive characterization of turbulent fluxes and land‐atmosphere interactions at a semi‐arid region in the Deccan Plateau of peninsular India is presented using 2‐year eddy covariance measurements. Contrary to previously reported results over the Indian region, surface energy partitioning is more into sensible heat flux than latent heat flux, even during the monsoon season. Irrespective of the seasons, the soil moisture and its response to rainfall drive the land‐atmosphere interactions and along with the net radiation, play crucial roles in deciding the surface fluxes and its partitioning. Time series comparison with ERA5 reanalysis data reveals the inadequate representation of land‐atmosphere interactions in ERA5 reanalysis over the peninsular Indian region, particularly the intensity and duration of rainfall and the feedbacks of soil moisture to the atmosphere. The surface energy balance closure improves by ∼3% when the soil heat storage term is considered and is the highest when the height and scatter of the roughness elements around the measurement site are the lowest. The influence of rainfall on energy balance closure is lower as compared to land surface heterogeneity. The present study also fills an existing gap of validating the surface fluxes and its partitioning in ERA5 reanalysis in the tropics and will provide deeper insights on the land‐atmosphere interactions in tropical semi‐arid regions. Plain Language Summary: The interactions between the surface of the Earth and the atmosphere above it controls the weather and climate of a region to a large extent. Accurately capturing such interactions in weather and climate models is arduous due to (a) the limited measurements on the partitioning of solar energy that reaches the surface and (b) the surface heterogeneities. Such measurements over different terrains and its comparison with various global data sets are essential to improve the climate predictions. Making use of 2‐year observations, we report the anomalous partitioning of surface energy at a semi‐arid region in India and how the rainfall and soil moisture play crucial roles in regulating it. Large differences between the observations and a modeled data set in the duration and intensity of rainfall and the energy partitioning at the surface are delineated along with the significant influence of the vegetation and soil heat storage. These results will be helpful in improving the weather and climate model simulations over the semi‐arid regions in the tropics. Key Points: Contrary to previous reports over the Indian region, partitioning of surface fluxes is more to sensible heat flux than latent heat fluxMeasurements reveal large differences in the rainfall duration and intensity and land‐atmosphere interactions compared to reanalysis dataEnergy balance closure is inversely proportional to the height of the roughness elements and their scatter around the measurement site [ABSTRACT FROM AUTHOR]

Considerable errors may be introduced in storm intensity estimations and their subsequent applications if raw surface wind speed records are not corrected to properly account for exposure effects. This study investigates the calculation of exposure correction factors (ECFs$$ \mathrm{ECFs} $$) by different theoretical and code‐based models. Estimation of the roughness length z0$$ {z}_0 $$ based on the suitable gustiness model is provided, as this metric is involved in calculating ECFs$$ \mathrm{ECFs} $$. The sensitivity of the z0$$ {z}_0 $$ estimation to the input parameters is analysed. A comprehensive evaluation of ECF$$ \mathrm{ECF} $$ models is made, which includes the World Meteorological Organization (WMO) model with various blending heights zb$$ {z}_{\mathrm{b}} $$, Biétry model, the power‐law model, the Engineering Sciences Data Unit model, the models in Chinese, Japanese, Eurocode and the International Organization for Standardization codes, as well as the combination of the WMO formula with two gustiness models (He model and Ashcroft model) respectively. It is found that the most appropriate model in practice for calculating ECFs$$ \mathrm{ECFs} $$ is provided by the combined application of the He gustiness model and WMO ECF$$ \mathrm{ECF} $$ formula with a blending height, zb,of80m$$ {z}_{\mathrm{b}},\mathrm{of}\kern1.00em 80\mathrm{m} $$. [ABSTRACT FROM AUTHOR]

Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

There are few reports in the literature regarding wind speed near the ground. This work presents a model for wind speed from 4 m above the ground, based on year-round measurements in two meteorological towers. Each tower is equipped with anemometers at five heights, as well as thermometers and pressure and relative humidity sensors. The data is processed using Eureqa artificial intelligence software, which determines the functional relationship between variables using an evolutionary search technique called symbolic regression. Using this technique, models are found for each month under study, in which height and temperature are the variables that most affect wind speed. The model that best predicts the measured wind speeds is then selected. A polynomial function directly proportional to height and temperature is identified as the one that provides the best predictions of wind speed on average, within the rough sub-layer. Finally, future work is identified on testing the model at other locations. [ABSTRACT FROM AUTHOR]

Based on morphological methods, MODIS satellite remote sensing data were used to establish a dataset of the local roughness length (Z0) of vegetation-covered surfaces in Guangdong Province. The local Z0 was used to update the mesoscale Weather Research and Forecasting (WRF) model in order to quantitatively evaluate its impact on the thermodynamic environment of vegetation-covered surfaces. The specific results are as follows: evergreen broad-leaved forests showed the largest average Z0 values at 1.27 m (spring), 1.15 m (summer), 1.03 m (autumn), and 1.15 m (winter); the average Z0 values of mixed forests ranged from 0.90 to 1.20 m; and those for cropland-covered surfaces ranged from 0.17 to 0.20 m. The Z0 values of individual vegetation coverage types all exhibited relatively high values in spring and low values in autumn, and the default Z0 corresponding to specific vegetation-covered surfaces was significantly underestimated in the WRF model. Modifying the default Z0 of surfaces underlying evergreen broad-leaved forests, mixed forests, and croplands in the model induced only relatively small changes (

Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is desirable that a surface layer scheme in an atmospheric numerical model is consistent with an atmospheric boundary layer scheme incorporated in the same model. In this study, stability functions based on Monin-Obukhov similarity theory for momentum and heat, f m and f h, in the stable surface layer are derived from the Mellor-Yamada-Nakanishi-Niino (MYNN) scheme. The resulting stability functions are approximated by f m = 1 + 4.8z/L and f h = 0.74 + 6.0z/L, which can be analytically integrated with respect to height z to obtain momentum and heat fluxes, where L is the Obukhov length. The fluxes thus, obtained are compared with those acquired from stability functions in four previous studies: they are nearly the same as those from two of them, and show better agreement with observational data of the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) over sea ice than those from the other two studies. Detailed comparisons of the results of the MYNN scheme with the SHEBA data suggest that significant variations of the fluxes observed during "winter" when the ice was covered with dry snow may have been caused by those of the surface roughness around the observational site. The stability functions obtained from the MYNN scheme predict that the bulk and flux Richardson numbers approach critical values of 0.26 and 0.21, respectively, in the limit of z/L ¥. These critical values result from the Kolmogorov hypothesis applied to the turbulent dissipation in the MYNN scheme and are considered to correspond to a transition from Kolmogorov to non-Kolmogorov turbulence. [ABSTRACT FROM AUTHOR]

This paper discusses how the incorporation of high-resolution ground coverage dataset ESA WorldCover into a wind flow field and wake simulation calculation, as well as the use of the coupled wake model for wind farm output simulation, can improve the accuracy of wind resource assessment using engineering examples. In the actual case of grid-connected wind farms in central China, SCADA wind speed data is reconstructed to the free flow wind speed in front of the wind turbine impeller using the transfer function of the nacelle, and the wind farm is modeled using OpenWind software, simulating the wind speed at the height of each wind turbine hub and each wind turbine output. The results show that when other initial data are consistent, using ESA’s high-precision land cover dataset WorldCover 10 m to make roughness lengths which improves the wind farm output simulation accuracy by 8.91%, showing that it is worth trying to apply WorldCover 10 m to the wind farm simulation design. At the same time, this case is used to compare and analyze the application of the Eddy-Viscosity wake model and the two coupled wake models based on the Eddy-Viscosity wake model. The results show that the coupled wake model will have higher accuracy than the Deep Array Eddy Viscosity wake model and it is 1.24% more accurate than the Eddy Viscosity wake model, and the ASM Eddy Viscosity wake model is 5.21% more accurate than the Eddy Viscosity wake model.

The analytical equation based on Monin-Obukhov (M-O) similarity theory ( i.e. , wind profile equation) has been adopted since 1970s for using in the prediction of wind vertical profile over flat terrains, which is mature and accurate. However, its applicability over complex terrains remains unknown. This applicability signifies the accuracy of the estimations of aerodynamic parameters for the boundary layer of non-flat terrain, such as zero-displacement height ( d ) and aerodynamic roughness length ( z 0 ), which will determine the accuracy of frequency correction and source area analysis in calculating carbon, water, and trace gas fluxes based on vorticity covariance method. Therefore, the validation of wind profile model in non-flat terrain is the first step to test whether the flux model needs improvement. We measured three-dimensional wind speed data by using the Ker Towers (three towers in a watershed) at Qingyuan Forest CERN in the Mountainous Region of east Liaoning Province, and compared them with data from Panjin Agricultural Station in the Liaohe Plain, to evaluate the applicability of a generalized wind profile model based on the Monin-Obukhov similarity theory on non-flat terrain. The results showed that the generalized wind profile model could not predict wind speeds accurately of three flux towers separately located in different sites, indicating that wind profile model was not suitable for predicting wind speeds in complex terrains. In the leaf-off and leaf-on periods, the coefficient of determination ( R 2 ) between observed and predicted wind speeds ranged from 0.12 to 0.30. Compared to measured values, the standard error of the predicted wind speeds was high up to 2 m·s -1 . The predicted wind speeds were high as twice as field-measured wind speed, indicating substantial overestimation. Nevertheless, this model correctly predicted wind speeds in flat agricultural landscape in Panjin Agricultural Station. The R 2 between observed wind speeds and predicted wind speed ranged from 0.90 to 0.93. The standard error between observed and predicted values was only 0.5 m·s -1 . Results of the F -test showed that the root-mean-square error of the observed and predicted wind speeds in each secondary forest complex terrain was much greater than that in flat agricultural landscape. Terrain was the primary factor affecting the applicability of wind profile model, followed by seasonality (leaf or leafless canopy). The wind profile model was not applicable to the boundary-layer flows over forest canopies in complex terrains, because the d was underestimated or both the d and z 0 were underestimated, resulting in inaccurate estimation of aerodynamic height.

By utilizing meteorological local objective analysis (LA) data on a local scale, this study investigated the spatial distribution of the power law index (PLI) of the mean wind speed profile in an urban area around Tokyo Bay in Japan. First, the reliability of the LA data was verified by comparison with observational data. The PLIs of the area for the 16 wind directions at a spatial resolution of 5 km were then estimated using LA data. Under neutral atmospheric conditions, the effects of the roughness length and terrain elevation on the PLI were investigated, and the spatial distribution characteristics of the PLI were analyzed. The results showed that the LA data were consistent with the observational data, indicating that high-precision LA data produced by data assimilation can be a practical supplement to observational data over urban areas. The influence of wind direction on the PLI was evident in the urban area. Furthermore, the metropolis appeared to affect the wind profile significantly when it was within the fetch of other cities, resulting in a larger PLI in the surrounding area. Because the PLI has complex spatial heterogeneity, in addition to urban substrate roughness, changes in terrain elevation and wind direction are thought to affect the PLI significantly. Therefore, generalizing the wind profile characteristics of large-area urban regions using local on-site observational data is not recommended. • The local objective analysis data were used to investigate the power law index of urban wind profiles. • The spatial distribution of the power law index in the urban area around Tokyo Bay was estimated. • Influence of the roughness length, wind direction, and terrain altitude on the wind profile was investigated. [ABSTRACT FROM AUTHOR]

Roughness length (Z 0) is a fundamental parameter in atmospheric boundary layer theory that affects the transfer of momentum and heat. However, this parameter in urban areas in the WRF model is typically assigned a fixed value. In a previous study, we developed a Z 0 database for the heterogeneous urban underlying surface of Guangzhou and demonstrated that its application in the WRF model had significantly improved the simulations of wind speed. In this study, the impact of Z 0 update on the dynamic and thermal environment in Guangzhou urban areas is investigated through two numerical experiments: the base experiment applies the model-default Z 0 value (0.5 m) for the urban areas and the sensitivity one uses a heterogeneous Z 0 map (with higher Z 0 values in most urban areas) estimated in the previous study. The results show that the temperature and relative humidity at 2 m height are not sensitive to this Z 0 modification. For the dynamic environment, the modification of Z 0 decreases the wind speed at 10 m height and increases the friction velocity. The reduction of horizontal wind speed due to Z 0 increases reaches heights of several hundred meters, especially below a height of 400 m (950 hPa). Additionally, the updated Z 0 leads to an increase in the turbulent momentum exchange coefficient over the urban underlying surface, resulting in a more vigorous turbulent mixing and elevated planetary boundary layer height. For the thermal environment, the Z 0 increases result in a higher turbulent heat exchange coefficient near the surface layer, which contributes to the vertical heat flux transport. Moreover, the Z 0 increase enhances the sensible heat flux during daytime and reduces the land surface temperature and ground heat flux in Guangzhou central urban area. Due to the reduced heat storage during the daytime, the amount of heat released at night decreases accordingly, thus causing a reduction in the land surface temperature at night and a decrease in the sensible heat flux. This study provides a comprehensive understanding of the sensitivity of the thermodynamic environment to the urban Z 0 increase and reconfirms the significance of a realistic Z 0 dataset in atmospheric modeling. [Display omitted] • The effect of Z 0 modifications on spatiotemporal variations of meteorological factors was explored. • Horizontal wind speed reduction due to Z 0 increases reached heights of several hundred meters. • Surface energy balance was used to illustrate the impact of Z 0 increases during daytime and nighttime. [ABSTRACT FROM AUTHOR]

The increasing human activity in forested regions requires a better understanding of the wind conditions. This paper aims to improve the wind simulation in forested regions of complex terrain, and thereby to investigate the effect of forest on wind characteristics. Considering the complexity of the surface, simulations were carried out covering different parameterization schemes sets using Weather Research and Forecasting model (WRF). The results indicate that Noah-MP scheme and YSU scheme are recommended for a mesoscale wind simulation in forested regions of complex terrain. Moreover, due to the complexities of land surface with seasonally-varied roughness length (RL) and leaf area index (LAI), localized LAIs and RLs would significantly improve wind field simulation. Comparisons demonstrated that the modified RLs, which can reshape the wind speed distribution, have greater impact than LAI on the wind field simulation in the near-surface level. The findings can be further exploited in the wind damage assessment for the infrastructures, as well as wind power assessment in forested regions. • WRF simulation is conducted to study surface wind field in forested regions. • Roughness length and LAI are modified to better represent forest canopy. • Combination of Noah-MP, YSU scheme and modified roughness and LAI produces optimum. [ABSTRACT FROM AUTHOR]