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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 (

This report presents the directional dependence of surface scaling parameters, namely, roughness length and corresponding friction velocity, for neutral category at the Tarapur coastal site. The average roughness length of the lowest value of 0.5 m in the west (W) direction and the highest value of 0.885 m in the N direction has been observed and average friction velocity of the lowest value 0.39 m/s in the W direction and the highest value 0.73 m/s in the NW direction was observed for 2019. Sector average turbulent kinetic energy was estimated to be 1.413 m2/s2 and its dissipation rate as 0.33 m2/s3 for the 10 m elevation from the surface. Surface drag coefficient for the 10 m height was 0.0229 for the smooth ocean surface and 0.0255 for the land surface was observed for the Tarapur coastal site.

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.

A model for the roughness length and its correlation with the roughness shear stress on organized rough walls of varying geometry are presented and verified. The roughness length is nondimensionalized by the characteristic roughness length and is expressed as a function of roughness density with a wake-interference parameter. The dimensionless roughness length is independent of Reynolds number. When the model is applied to the whole range of roughness densities, the rough walls can be smooth, transitionally rough, and fully rough. A large number of data from classical experiments and recent simulations are analyzed to evaluate the proposed correlations, which are found to be consistent with the analyzed datasets. The proposed expression for the dimensionless roughness length and the expression for the dimensionless roughness shear stress, proposed previously by the author (Boundary-Layer Meteorology, 2020, Vol. 174, 393–410), are found to be identical in form. Numerous extant measurements of the two roughness parameters can be reproduced when the wake-interference parameters in the two models are treated as identical. The parameters of the roughness-length model are closely related to the geometry of the roughness elements. Different types of roughness elements can be distinguished by the values of the parameters. These results provide the foundation for constructing the unified roughness model for organized rough walls of varying geometry. [ABSTRACT FROM AUTHOR]

Monitoring of dry vegetation in arid and semi-arid regions is crucial in environmental investigations such as assessments of wind erosion risk, livestock forage, and fire risk. However, there has been little research into estimating the coverage and mass of dry (non-photosynthetic) vegetation. In our study area at Tsogt-Ovoo (TsO) in the northern Gobi Desert, Mongolia, we used MODIS data to compare observed dry vegetation cover (VCd_obs) and mass (Md_obs) with values estimated from the Normalized Difference Vegetation Index (NDVI) and six other potential Short Wavelength InfraRed (SWIR) dry vegetation indices. Of the seven vegetation indices, the Soil Tillage Index (STI) and Normalized Difference Tillage Index (NDTI), both of which are calculated from SWIR bands 6 and 7, provided good estimates of VCd_obs and Md_obs. Our comparisons of observed roughness length (z0) and threshold friction velocity (u*t) for sand saltation at stony and non-stony sites with dry vegetation cover determined from STI verified its suitability for estimating VCd(STI). At both sites, the observed z0and u*tincreased with increasing estimated VCd(STI). Based on their relationships with STI, we predicted values of z0and u*tin the absence of dry vegetation that were in accordance with published data. The threshold wind speeds at 10 m height derived from u*tat both the stony and non-stony sites were reasonably close to the value that is commonly used in dust models. Thus, we verified that STI is a suitable index for estimating the amount of dry vegetation in the Gobi Desert and, potentially, in other arid and semi-arid regions. Although the relationships of z0and u*twith STI require further validation, it appears that the use of STI can improve future wind erosion risk assessments in arid and semi-arid environments.

• LiDAR-based roughness parameterization is introduced in Evapotranspiration (ET) model. • Original SEBS overestimate LE and underestimate H compared to in-situ EC observations. • SEBS LiDAR perform better than SEBS in estimating LE and H compared to EC observations. • Canopy height controls the output of SEBS ET model. • LiDAR can significantly improve the accuracy of roughness lengths in ET model. Spatially distributed information of actual Evapotranspiration (ET) is essentially required for various applications in agriculture, as well as studies related to water balance. An Energy Balance model that uses optical and thermal remote sensing datasets is appropriate for the spatially distributed estimation of ET, which is primarily controlled by local environmental conditions. In this study, we use the Surface Energy Balance System (SEBS), which is an Energy Balance model, to estimate an improved actual ET, by integrating canopy height information obtained from ICESat/GLAS, the first space-borne LiDAR satellite. Our model estimates latent heat flux (LE) as a residual of energy balance, while sensible heat flux (H) is estimated based on Monin–Obukhov similarity theory. The spatial variability of H and LE estimated from Landsat TM/ETM+ images were compared with eddy covariance (EC) based in situ flux tower observations, in order to document the SEBS model uncertainties in three forest sites in the East and Southeast Asian ecosystem. We identified that canopy height (h c) is one of the critical parameters that can induce uncertainties in SEBS model estimations. Therefore, h c obtained from LiDAR was introduced in parameterization of the roughness length for momentum transfer (z 0m). In situ based h c obtained from flux tower stations, and the normalized difference vegetation index based formulation of h c proposed by Su (2001), were also introduced in the SEBS z 0m parameterization. Root mean square error of LiDAR integrated SEBS (SEBS LiDar) for estimated H values reduced by (20, 45, and 23)% compared to Landsat integrated SEBS (SEBS Landsat), and (18, 7, and 9)% compared to In situ integrated SEBS (SEBS Insitu) at the three selected forest sites (SMC, QYZ, and SMF), respectively, while the mean coefficient of determination values for the estimated LE improved by (9.09 and 5.88)% compared to SEBS Landsat and SEBS Insitu , respectively, with reference to ground-based flux tower observations. Our analysis reveals that LiDAR-based parameterization of z 0m can significantly increase the accuracy of estimated roughness lengths within an ET model, which can therefore improve the accuracy of the estimated turbulent heat fluxes. SEBS LiDAR was further evaluated for the spatially distributed mapping of actual ET. We have observed that ET estimated by SEBS Landsat overestimated in forest sites compared to EC observations; however, LiDAR-integrated SEBS marginally improved the accuracy of ET, thereby leading to an improvement in the mean correlation value of 0.87 and mean normalized standard deviation value of 0.93 approaching unity based on Taylor diagram, which more closely approximates the actual ground-based measurements. The proposed methodology overcomes the current limitation in the energy balance models in estimating roughness lengths, by providing accurate formulation of h c by specifically incorporating LiDAR measurements in areas of tall vegetation canopies. The operational improvement in roughness lengths by next-generation SEBS LiDAR model provides an opportunity to improve the estimation accuracy of water and energy fluxes, specifically ET. Overall, our proposed SEBS LiDAR model provides a benchmark that is useful to policy makers and water resource managers in devising a plan for sustainable use of water resources in the East Asian region, as well as other similar ecosystems. [ABSTRACT FROM AUTHOR]

Statistical methods are employed to assess the extent to which measurements of temperature using downward looking infrared thermometry (T0) are indicative of the effective boundary between the air and the subsurface environment. An effective interfacial surface temperature (Te) is determined from consideration of in-air (Ta) and subsurface (Ts) temperature data, being that which best satisfies the multi-media (air and soil) flux relationships. Using data obtained in studies conducted in Ohio in 2015, it is shown that during the daytime measured values of T0 exceeded Te by an amount reaching a near-noon maximum of about 2 °C when the crop (maize) was fully grown. Night-time observations indicated a near equality of T0 and Te, although often equality appears threatened by the presence of strongly stable layers in air near the surface. Ramifications of the observed differences are discussed, with particular attention to implications regarding determination of the thermal roughness length associated with the sensible heat flux. [ABSTRACT FROM AUTHOR]

Surface-layer stability is important in many processes, such as in the surface energy budget, atmospheric pollution, and boundary-layer parametrizations. Most previous studies on stability, however, conducted either theoretical or observational investigations at specific sites, thus leaving a gap with regard to the large-scale pattern. Here, wind-speed and temperature observations at multiple heights from the wind-tower network of China are used to estimate low-level stability during the 2009–2016 period. A series of data-quality-control procedures are conducted and data from 170 wind towers with more than 2 years of valid observations are selected. The degree of stability is classified by the Obukhov length, which is derived from the wind speed and temperature at 10 m and 70 m above ground level, combined with information regarding the roughness length. Overall, the occurrence frequency of surface-layer instability exhibits significant temporal and spatial variability, being particularly larger in spring and summer than in autumn and winter. The maximum frequency of summertime instability occurs in the time period 1000–1200 local solar time, approximately 2 h earlier than in autumn. Geographically, the peak instability frequency occurs much earlier in the day in north-west China than in other regions, likely owing to the arid and semi-arid land cover. Also noteworthy is the steady increase in instability frequency observed during the period analyzed here, likely resulting from the reduction in the vertical gradient of wind speed. Our findings call for explicit consideration of stability variability in the wind-energy industry and in fundamental boundary-layer investigations in China. [ABSTRACT FROM AUTHOR]

Basic wind velocity for civil engineering purpose is determinant for structural design under wind action. Basic wind velocity is obtained from data measurements at meteorological stations supposedly placed in ideal terrain conditions, and it is estimated by different statistical methods. Not all stations accomplish the ideal conditions, therefore, correction of the wind velocity values must be done. The main objective of this paper is to define a roughness correction factor for wind velocity in not ideal conditions, and to compare basic wind velocity obtained with proposed basic wind velocity for the Cuban territory at international studies. Two meteorological stations with different terrain roughness were selected, and the basic wind velocity for each one was obtained by applying the Method of Independent storms (MIS). Roughness was found through the Method of Classifications and the Morphometric Method, with the use of satellite LandSat8 images. Results show that modified basic wind velocities are similar for the two methods. The comparison with international studies proved a good correspondence only with one of the stations, hence it is recommended to extend the study to a greater number of stations. [ABSTRACT FROM AUTHOR]

Accurately predicting bare‐soil evaporation requires the proper characterization of the near‐surface atmospheric conditions. These conditions, dependent on factors such as surface microtopography and wind velocity, vary greatly and therefore require high‐resolution datasets to be fully incorporated into evaporation models. These factors are oftentimes parameterized in models through the aerodynamic resistance (ra), in which the vapor roughness length (z0v) and the momentum roughness length (z0m) are two crucial parameters that describe the transport near the soil‐atmosphere interface. Typically, when evaluating bare‐soil evaporation, these two characteristic lengths are assumed equal, although differences are likely to occur especially in turbulent flows over undulating surfaces. Thus, this study aims to investigate the relationship between z0v and z0m above undulating surfaces to ultimately improve accuracy in estimating evaporation rate. To achieve this goal, four uniquely designed wind tunnel—soil tank experiments were conducted considering different wind speeds and undulation spacings. Particle image velocimetry (PIV) was used to measure the velocity field above the undulating surface in high resolution. Using the high‐fidelity data set, the logarithmic ratio of z0v to z0m is determined and used to estimate ra. Results confirm that these lengths differ significantly, with the logarithmic ratio roughly ranging from −15 to −5 under the conditions tested. PIV‐measured results demonstrate this ratio is closely tied to the mass and momentum transport behaviors influenced by surface undulations. Using the data‐integrated formulation of ra, predictions of evaporation rate were prepared for both the laboratory and lysimeter experiments, demonstrating the efficacy of the proposed approach in this study. Key Points: Particle image velocimetry (PIV) was successfully used to capture the velocity and Reynolds stress fields above undulating surfacesThe logarithmic ratio of the vapor to the momentum roughness length roughly ranging from −15 to −5 under the conditions testedPIV demonstrate the logarithmic length ratio is closely tied to the mass and momentum transport behaviors influenced by surface undulations [ABSTRACT FROM AUTHOR]

The mean wind speed at which the stable boundary layer (SBL) experiences a turbulence regime transition (Vr) depends on other flow characteristics, such as its thermal stability. Here, Vr variability is examined both at a single site and across sites using three multiple‐level datasets: Santa Maria, Cooperative Atmosphere–Surface Exchange Study–1999 (CASES‐99), and Fluxes over Snow Surfaces (FLOSS II). A method to determine Vr is introduced and validated. It is taken as the mean wind speed at which the vertical gradient of the turbulence velocity scale switches sign. Emphasis is given to the control exerted on Vr by quantities that are external to the SBL, such as radiation, roughness, and soil properties. In each of the experiments, Vr increases with net radiative loss at the surface (Rn) at a rate that is site‐dependent. It also increases for smaller roughness lengths, as indicated by its wind direction dependence. No conclusive relationship has been found between Vr and downward longwave radiation observed at the surface. The across‐site comparison indicates that soil heat capacity influences the rate at which Vr increases with Rn. [ABSTRACT FROM AUTHOR]

For a family of relatively common problems in micrometeorology, whose forms previously required iterative or indirect treatment, analytical solution is possible via the Lambert-W function. Use of this function reduces computational time and the need for approximations, while offering a clearer view of the character and solution of such problems. This note provides a generalized form for such problems, and demonstrates its use for three applications: internal boundary-layer growth due to a change in surface roughness; flow displacement over a canopy; and determination of friction velocity and roughness length over the sea. [ABSTRACT FROM AUTHOR]

This report presents the directional dependence of surface scaling parameters, namely, roughness length and corresponding friction velocity, for neutral category at the Tarapur coastal site. The average roughness length of the lowest value of 0.5 m in the west (W) direction and the highest value of 0.885 m in the N direction has been observed and average friction velocity of the lowest value 0.39 m/s in the W direction and the highest value 0.73 m/s in the NW direction was observed for 2019. Sector average turbulent kinetic energy was estimated to be 1.413 m2/s2 and its dissipation rate as 0.33 m2/s3 for the 10 m elevation from the surface. Surface drag coefficient for the 10 m height was 0.0229 for the smooth ocean surface and 0.0255 for the land surface was observed for the Tarapur coastal site. [ABSTRACT FROM AUTHOR]

The ability of forecasting systems to simulate tropical cyclones is still insufficient, and currently, there is an increased interest in improving model performance for intense tropical cyclones. In this study, the impact of reducing surface drag at high wind speeds on modeling wind and wave conditions during the super Typhoon Lingling event over the northwest Pacific Ocean in 2019 is investigated. The model response with respect to the parameterization for momentum exchange at the ocean surface is demonstrated using a fully coupled regional atmosphere model (the Consortium for Small-Scale Modeling-Climate Limited-area Modeling, CCLM) and a wind wave model (WAM). The active two-way coupling between the atmosphere and ocean waves model is enabled through the introduction of sea state-dependent surface drag into the CCLM and updated winds into the WAM. The momentum exchange with the sea surface is modeled via the dependency of the roughness length (Z0) on the surface stress itself and, when applicable, on the wind speed. Several high-resolution runs are performed using one-way or two-way fully coupled regional atmosphere-wave (CCLM-WAM) models. The model simulations are assessed against the best track data as well as against buoy and satellite observations. The results show that the spectral nudging technique can improve the model’s ability to capture the large-scale circulation, track and intensity of Typhoon Lingling at regional scales. Under the precondition of large-scale constraining, the two-way coupling simulation with the proposed new roughness parameterization performs much better than the simulations used in older studies in capturing the maximum wind speed of Typhoon Lingling due to the reduced drag at extreme wind conditions for the new Z0.

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.

The surface enthalpy fluxes (latent and sensible heat fluxes) provide the necessary energy to intensify tropical cyclones (TCs). The surface momentum fluxes modify the intensity of TCs. Various parameters affect the surface fluxes. Drag and enthalpy exchange coefficients are known as parameters that lead to ambiguity in the surface fluxes. Thus, for simulating a TC, various drag and enthalpy exchange coefficients are tested in numerical simulations. Exchange coefficients directly relate to roughness lengths. The main goal of this study was comparing derived roughness lengths of the COAWST (WRF-SWAN online coupling) and WRF models with one another. The TC Gonu formed over the Arabian Sea in 2007 was selected for this study. Employing self-reliant WRF, it is found that track and intensity of the TC Gonu can be best simulated when Donelan parameterization is applied for momentum roughness length and Large-Pond parameterization for enthalpy roughness length. In the second section, simulations were conducted in the coupled mode using the COAWST model with the Large-Pond parameterization (for the enthalpy roughness length). Results cleared that the use of Oost parameterization leads to a high overestimation of simulated momentum roughness length compared with other parameterizations while both the Drennan and Taylor parameterizations were somewhat close to reality. Differences of simulated maximum 10-m wind speed between the Oost parameterization and other parameterizations were more than differences of their simulated minimum central pressure. These results proved that the momentum roughness length affects the maximum 10-m wind speed more significantly than the minimum central pressure. In the last section, a simulation was performed using the COAWST model with the Donelan–Large-Pond parameterization. In this simulation, only 10-m wind speed from the WRF model transferred to the SWAN model. The results showed that simulated wave heights in the open ocean were in good agreement with the results of other researchers. In general, the SWAN model performance is evaluated satisfactorily while the parameterizations using the wave information need to be more investigated. [ABSTRACT FROM AUTHOR]

This study makes use of data from six meteorological masts to examine five different data sources of roughness lengths. The data sources can be applied in most regions of the world. The consequences of applying wrong roughness lengths can impact the business case of a wind project. The experiment confirmed the preliminary expectation, as the optimized roughness approach provided better results than the remaining four approaches and, furthermore, was able to treat different tree heights. The initial test was conducted using a spatial resolution of 20 m for optimized roughness approach, while the other data sources used a greater resolution. As a response, optimized roughness approach was reused for the other spatial resolutions showing better results than the remaining approaches. One other remarkable finding associated with this study was the relationship between spatial resolution and errors in the estimation, as a resolution above 100 m provided random results with no relationship whatsoever. [ABSTRACT FROM AUTHOR]

In a steady, spatially homogeneous neutral stability flow dominated by mechanical turbulence, the friction velocity ( u ∗ ) and the roughness length (z0) can be estimated by applying linear regression to measurements of wind speed (u) at several heights (z). Surface-layer wind profile plots in the scientific literature normally have ln(z) on the vertical axis and u on the abscissa, which might suggest a linear regression, such as the ordinary least-squares method, which minimizes the vertical residuals, i.e., the ln(z) deviations, from the fitted line. Here, we show that ordinary least-squares fitting of the profile data is sensitive to the choice of the variable whose residuals are being minimized, and that the linear regression should be computed as u versus ln(z), i.e., minimizing the u deviations. This is equivalent to ln(z) being the independent variable and u the dependent variable. The differences in the estimated values of u ∗ and z0 compared to those resulting from the ln(z) versus u linear regression can be expressed as a function of the coefficient of determination (r2) of the wind-profile data. Applying the ordinary least-squares method while minimizing the deviations of ln(z) leads to systematic overestimation of the u ∗ and z0 values. Using these values as input into the atmospheric dispersion model AERMOD leads to increased shear-induced turbulence and consequently enhanced dilution of the plume. [ABSTRACT FROM AUTHOR]