Vertical Profiles Of Wind Speed Research Articles

Optical turbulence and wind speed distributions above the Tibetan Plateau from balloon-borne microthermal measurements

ABSTRACT The vertical profiles of wind speed and the optical turbulence are critical to the design and operation of a new generation of highly sophisticated astronomical telescopes and adaptive optics instrumentation. We present the first study of the temporal evolution behaviours and probability distributions of wind speed [V(h) profiles, as well as the 200 hPa pressure level wind speed, V200] and optical turbulence [$C_n^2(h)$ profiles, and the most relevant integrated astronomical parameters derived from $C_n^2(h)$ profiles, i.e. the seeing ε, the isoplanatic angle θAO, the wavefront coherence time τAO, the average velocity of turbulence VAO, and the seeing layer height hAO] above the Dachaidan site of the Tibetan Plateau. The field campaigns of wind speed and optical turbulence were collected using the balloon-borne microthermal measurement system. From the whole field campaigns, the results are remarkable: The median VAO is 21.1 m s−1, the median V200 is 32.5 m s−1, the median hAO is 7566 m, the median ε is 1.04 arcsec (below 1.00 arcsec 52 per cent of the time), the median θAO is 0.74 arcsec, and the median τAO is 1.33 ms; these conditions are comparable to some of the best astronomical observatories in the world. In particular, the linear relationship of average velocity and 200 hPa level wind at this site is VAO = 0.627V200. In this study, we flag the temporal evolution and probability distribution feature of wind speed, optical turbulence profile, and the relevant integrated astronomical parameters for astronomical applications.

Urban-Scale Computational Fluid Dynamics Simulations with Boundary Conditions from Similarity Theory and a Mesoscale Model

Mesoscale numerical weather prediction models usually provide information regarding environmental parameters near urban areas at a spatial resolution of the order of thousands or hundreds of meters, at best. If detailed information is required at the building scale, an urban-scale model is necessary. Proper definition of the boundary conditions for the urban-scale simulation is very demanding in terms of its compatibility with environmental conditions and numerical modeling. Here, steady-state computational fluid dynamics (CFD) microscale simulations of the wind and thermal environment are performed over an urban area of Kozani, Greece, using both the k-ε and k-ω SST turbulence models. For the boundary conditions, instead of interpolating vertical profiles from the mesoscale solution, which is obtained with the atmospheric pollution model (TAPM), a novel approach is proposed, relying on previously developed analytic expressions, based on the Monin Obuhkov similarity theory, and one-way coupling with minimal information from mesoscale indices (Vy = 10 m, Ty = 100 m, L*). The extra computational cost is negligible compared to direct interpolation from mesoscale data, and the methodology provides design phase flexibility, allowing for the representation of discrete urban-scale atmospheric conditions, as defined by the mesoscale indices. The results compared favorably with the common interpolation practice and with the following measurements obtained for the current study: SODAR for vertical profiles of wind speed and a meteorological temperature profiler for temperature. The significance of including the effects of diverse atmospheric conditions is manifested in the microscale simulations, through significant variations (~30%) in the critical building-related design parameters, such as the surface pressure distributions and local wind patterns.

Influence of turbulence models on the dynamic response of a semi-submersible floating offshore wind platform

With the aim of evaluating the effects of the selection of the wind turbulence model on the dynamic response of a semi-submersible floater supporting the DTU 10 MW RWT, we ran aero-hydro-servo-elastic simulations employing the OASIS code developed at IHCantabria. For each of the 4 sea states selected, apart from the reference case with only wave loads, we analysed 30 different realizations with coupled wind and wave loads for each of the 7 full-field turbulent winds generated by the turbulence simulator TurbSim: Kaimal and von Kármán spectral models with three different turbulence classes each and the API turbulence model.From the resulting platform motions and mooring line dynamics, it can be concluded that the selection of the wind turbulence model is not trivial. At U0=5.83 m/s, the obtained results show a high dependence on the turbulence class. However, as the wind speed increases and the wind turbine achieves the rated speed, the impact of the turbulence intensity is drastically reduced, and the design tension is dominated by the thrust force and thus by the vertical wind speed profile. The highest design tension of the windward mooring lines is obtained with the API model at U0=8.75 m/s (at least 357 Tm).

Site-targeted evaluation of SWIFT-RIMPUFF for local-scale air dispersion modeling around Sanmen nuclear power plant based on multi-scenario wind tunnel experiments

The SWIFT-RIMPUFF is composed of the Stationary Wind Fit and Turbulence model and the Risø Mesoscale PUFF model, which has explicit building modules for atmospheric dispersion modeling. A comprehensive evaluation of SWIFT-RIMPUFF was performed to the vertical profiles of wind speed, horizontal wind and concentration fields based on six wind tunnel experiments of the Sanmen nuclear power plant site, where the topographies are featured with surrounding mountains, sea, and dense buildings. The results demonstrate that the simulated wind flows reproduce the detail distribution of both speed and direction, which agrees well with the observations in both the building area and diverse topographies. For the concentration fields, the biases of plume axes around the release position are visible in half of the scenarios, leading to inaccurate predictions of the highest observations. The global FAC2 (0.587), FB (0.172), and PCC (0.752) illustrate the capability of SWIFT-RIMPUFF for local-scale modeling at this site.

A temporal model for vertical extrapolation of wind speed and wind energy assessment

Accurate wind speed estimates at turbine hub height are critical for wind farm operational purposes, such as forecasting and grid operation, but also for wind energy assessments at regional scales. Power law models have widely been used for vertical wind speed profiles due to their simplicity and suitability for many applications over diverse geographic regions. The power law requires estimation of a wind shear coefficient, α, linking the surface wind speed to winds at higher altitudes. Prior studies have mostly adopted simplified models for α, ranging from a single constant, to a site-specific constant in time value. In this work we (i) develop a new model for α which is able to capture hourly variability across a range of geographic/topographic features; (ii) quantify its improved skill compared to prior studies; and (iii) demonstrate implications for wind energy estimates over a large geographical area. To achieve this we use long-term high-resolution simulations by the Weather Research and Forecasting model, as well as met-mast and radiosonde observations of vertical profiles of wind speed and other atmospheric properties. The study focuses on Saudi Arabia, an emerging country with ambitious renewable energy plans, and is part of a bigger effort supported by the Saudi Arabian government to characterize wind energy resources over the country. Results from this study indicate that the proposed model outperforms prior formulations of α, with a domain average reduction of the wind speed RMSE of 23–33%. Further, we show how these improved estimates impact assessments of wind energy potential and associated wind farm siting.

In situ measurements and neural network analysis of the profiles of optical turbulence over the Tibetan Plateau

ABSTRACT The vertical profile of $C_n^2$ is the main factor for accurate astronomical observation and laser communication, however, hardware-based instruments and associated data are not widely available due to logistical and financial issues. In this article, we developed an indirect method, a hybrid network structure which is a combination of the backpropagation neural network and the simulated annealing algorithm, to fit the vertical profile of $C_n^2$. Radiosonde measurements from a field campaign over the Tibetan Plateau at Dachaidan (37.7○N, 95.3○E, 3180 m ASL) were performed in 2020 August to estimate the accuracy of our model, during which a balloon-borne portable turbulence meteorological radiosonde was used to measure the atmospheric optical profiles. Besides, the integrated astronomical parameters (the coherence length r0, seeing ε0, isoplanatic angle θ0, and the wavefront coherence time τ0), derived from $C_n^2$ and wind-speed vertical profiles, are investigated for astronomical applications using the proposed model. In addition, quantitative evaluations such as the correlation coefficient, the root mean squared error, and the systematic bias are used to quantify the performance of our model. More interesting, this model is found to outperform a widely used external scale model for the prevalent atmospheric conditions and shows better correlation and reliable estimates.

Investigations of high-density urban boundary layer under summer prevailing wind conditions with Doppler LiDAR: A case study in Hong Kong

The high-density urban boundary layer (UBL) is one of the most complex atmospheric conditions, while the field data of UBL is limited due to the lack of suitable measurement methods. To better understand the UBL structures in high-density cities, a pioneering investigation is conducted in Hong Kong by Doppler wind LiDAR. Vertical wind speed profiles are measured at three locations: Cape D'Aguilar (upwind), University of Hong Kong (downtown), and Hong Kong University of Science and Technology (downwind). To address the weak wind conditions in summer, the prevailing southwest wind condition is selected as the subject of investigation. Based on the observations, the gradient height over Hong Kong is approximately 1.0–1.2 km. Below this height, the vertical wind speed profiles are significantly modified by surface morphologies. The power-law equation appropriately parametrizes the upwind (α = 0.1–0.15) and downwind (α = 0.27) profiles, but it has limitations when parametrizing the downtown profile. Deficiencies of the vertical wind speed profiles predicted by conventional meso-scale simulations and wind-tunnel experiments are revealed. These results provide researchers and engineers benchmarking data to refine their urban climate predictions. They generalize a better understanding of the UBL climates, which can be shared with other high-density cities.

Departure from Flux-Gradient Relation in the Planetary Boundary Layer

It is well known that when eddies are small, the eddy fluxes can be directly related to the mean vertical gradients, the so-called flux-gradient relation, but such a relation becomes weaker the larger the coherent structures. Here, we show that this relation does not hold at heights relevant for wind energy applications. The flux–gradient relation assumes that the angle (β) between the vector of vertical flux of horizontal momentum and the vector of the mean vertical gradient of horizontal velocity is zero, i.e., these vectors are aligned. Our observations do not support this assumption, either onshore or offshore. Here, we present analyses of a misalignment between these vectors from a Doppler wind lidar observations and large-eddy simulations. We also use a real-time mesoscale model output for inter-comparison with the lidar-observed vertical profiles of wind speed, wind direction, momentum fluxes, and the angle between the horizontal velocity vector and the momentum flux vector up to 500 m, both offshore and onshore. The observations show this within the height range 100–500 m, β=−18∘ offshore and β=−12∘ onshore, on average. However, the large-eddy simulations show β≈0∘ both offshore and onshore. We show that observed and mesoscale-simulated vertical profiles of mean wind speed and momentum fluxes agree well; however, the mesoscale results significantly deviate from the wind-turning observations.

Observations of Wintertime Low-Level Jets in the Coastal Region of the Laptev Sea in the Siberian Arctic Using SODAR/RASS

In 2014/2015 a one-year field campaign at the Tiksi observatory in the Laptev Sea area was carried out using Sound Detection and Ranging/Radio Acoustic Sounding System (SODAR/RASS) measurements to investigate the atmospheric boundary layer (ABL) with a focus on low-level jets (LLJ) during the winter season. In addition to SODAR/RASS-derived vertical profiles of temperature, wind speed and direction, a suite of complementary measurements at the Tiksi observatory was available. Data of a regional atmospheric model were used to put the local data into the synoptic context. Two case studies of LLJ events are presented. The statistics of LLJs for six months show that in about 23% of all profiles LLJs were present with a mean jet speed and height of about 7 m/s and 240 m, respectively. In 3.4% of all profiles LLJs exceeding 10 m/s occurred. The main driving mechanism for LLJs seems to be the baroclinicity, since no inertial oscillations were found. LLJs with heights below 200 m are likely influenced by local topography.

Estimation of marine winds in and around typhoons using multi-platform satellite observations: Application to Typhoon Soulik (2018)

Estimating horizontal winds in and around typhoons is important for improved monitoring and prediction of typhoons and mitigating their damages. Here, we present a new algorithm for estimating typhoon winds using multiple satellite observations and its application to Typhoon Soulik (2018). Four kinds of satellite remote sensing data, along with their relationship to typhoon intensity, derived statistically from hundreds of historical typhoon cases, were merged into the final product of typhoon wind (MT wind): 1) geostationary-satellite-based infrared images (IR wind), 2) passive microwave sounder (MW wind), 3) feature-tracked atmospheric motion vectors, and 4) scatterometer-based sea surface winds (SSWs). The algorithm was applied to two cases (A and B) of Typhoon Soulik and validated against SSWs independently retrieved from active microwave synthetic aperture radar (SAR) and microwave radiometer (AMSR2) images, and vertical profiles of wind speed derived from reanalyzed data and dropsonde observations. For Case A (open ocean), the algorithm estimated the realistic maximum wind, radius of maximum wind, and radius of 15 m/s, which could not be estimated using the reanalysis data, demonstrating reasonable and practical estimates. However, for Case B (when the typhoon rapidly weakened just before making landfall in the Korean Peninsula), the algorithm significantly overestimated the parameters, primarily due to the overestimation of typhoon intensity. Our study highlights that realistic typhoon winds can be monitored continuously in real-time using multiple satellite observations, particularly when typhoon intensity is reasonably well predicted, providing timely analysis results and products of operational importance.

Evaluation of Wind Energy Potential in a Sahelian Zone: A Case Study of Ouahigouya, Burkina Faso

This study investigates the characteristics of the wind energy potential in Ouahigouya, Burkina Faso. For this purpose, eleven-years data (2006-2016) of wind speed (at 10 m above ground level (AGL)) and surface temperature data from Burkina Faso meteorological agency and wind speed (50 m AGL) from the NASA were used. Based on the mean vertical profile of wind speed at monthly and annual scales, the Weibull function was used to characterize the wind speed frequency distribution and to calculate the wind power density. Major results indicate that the peaks of mean wind speeds are estimated at 3.51 m.s-1 (May) and 5.18 m.s-1 (March) for the 20 m and 50 m altitudes respectively. The mean annual wind speed at the 20 m AGL at the site is estimated at 2.87 m.s-1 while at 50 m AGL, a value of 4.33 m.s-1 is recorded. The estimated wind power density reveals that the largest amounts of energy are generally collected during the months corresponding to the dry season with peaks in March or May depending on the height. The amount of energy available at 20 m AGL varies from 32.90 W/m2 (September) to 84.97 W/m2 (May). At 50 m AGL, this value varies respectively from 68.68 W/m2 (August) to 346.47 W/m2 (March). Average annual power density amounts are estimated at 65.92 W/m2 at 20 m and 223.17 W/m2 at 50 m, respectively, for a growth rate of 70.46 %. In view of these results, the Ouahigouya site could be conducive to the installation of small and medium-sized turbines to supply rural communities with electrical energy.

Assessment of nonlinear effects of a deep subgrid lake with an atmospheric single‐column model

AbstractSome nonlinear aspects due to the coupling of a single column atmospheric model (SCM) with both a land‐surface model (LSM) and a lake model has lately been published by Goyette in 2017. In this previous study, the surface type abruptly changed from land to an open water surface. This article further investigates the potential of this SCM to explore the nonlinear effects through the analysis of the impacts of fractional land and open water surfaces on the surface fluxes and variables, as well as on the atmospheric air temperature, specific humidity, and wind speed vertical profiles, with an application to deep Lake Geneva, Switzerland. It is shown that the coupling methodology depending on the surface type produced realistic and coherent results and indicated that the mean fluxes and other relevant quantities may not be simply averaged on the basis of the fractional area of the land and that of the open water. If Lake Geneva relative surface area is prescribed to its observed value with respect to the model grid‐mesh size, the remaining being land surface, results showed maximum seasonal mean differences of 7.5 and 5.4 W·m−2 for the latent and sensible heat flux in Autumn respectively, 1.6°C, 0.8 g·kg−1 for the screen‐level air temperature and specific humidity in Autumn respectively, and 0.6 m·s−1 for the anemometer‐level windspeed in Winter with respect to the original land surface, owing to the different behaviour of the vertical turbulent transfer of heat, moisture and momentum but also to the different thermal and radiative characteristics of land and water surfaces.

Observation of Typhoon Hato based on the 356-m high meteorological gradient tower at Shenzhen

Field measurements of tropical cyclone (TC) at coastal areas are of great significance for the prevention and control of TC disasters. Despite the increasing efforts on this topic in the last years, studies based on fast-response records of TC wind at multiple heights over land are still limited. To this end, a 365 ​m high meteorological observation gradient tower at Shenzhen has been constructed and put into use since 2016. It is currently the tallest mast tower in Asia and the second tallest of this kind in the world. There are 13 levels of instruments installed in a range of 10 ​m–350 ​m on the mast, to measure various weather elements at a sampling frequency utmost to 10 ​Hz. This paper presents an observational study on the wind characteristics of Typhoon Hato which made landfall with an intensity of severe typhoon at a distance of ~90 ​km from the tower on Aug. 23, 2017. The vertical profiles of mean wind speed and typical wind turbulence quantities, i.e., gust factor, turbulence intensity, integral length scale, etc., are demonstrated and compared against provisions stipulated in wind load codes. The effects of thermal stratification on these quantities are stressed.

Assessing the Impact of Changes in Land Surface Conditions on WRF Predictions in Arid Regions

AbstractA thorough evaluation of the Weather Research and Forecasting (WRF) Model is conducted over the United Arab Emirates, for the period September 2017–August 2018. Two simulations are performed: one with the default model settings (control run), and another one (experiment) with an improved representation of soil texture and land use land cover (LULC). The model predictions are evaluated against observations at 35 weather stations, radiosonde profiles at the coastal Abu Dhabi International Airport, and surface fluxes from eddy-covariance measurements at the inland city of Al Ain. It is found that WRF’s cold temperature bias, also present in the forcing data and seen almost exclusively at night, is reduced when the surface and soil properties are updated, by as much as 3.5 K. This arises from the expansion of the urban areas, and the replacement of loamy regions with sand, which has a higher thermal inertia. However, the model continues to overestimate the strength of the near-surface wind at all stations and seasons, typically by 0.5–1.5 m s−1. It is concluded that the albedo of barren/sparsely vegetated regions in WRF (0.380) is higher than that inferred from eddy-covariance observations (0.340), which can also explain the referred cold bias. At the Abu Dhabi site, even though soil texture and LULC are not changed, there is a small but positive effect on the predicted vertical profiles of temperature, humidity, and horizontal wind speed, mostly between 950 and 750 hPa, possibly because of differences in vertical mixing.

Flux-gradient relation and atmospheric wind profiles — an exploration using WRF and lidars

A common closure for the planetary boundary layer in numerical weather models assumes a direct relation between turbulent fluxes and the mean wind vertical gradient, i.e., the flux-gradient relation or K-theory. This assumption implies that the angle β between the momentum stress vector and the mean gradient of the velocity vector are aligned, i.e., β = 0°. This is not what we observe from measurements. We quantify the misalignment of β in offshore conditions using measurements from a long-range Doppler profiling lidar and numerical simulations from the New European Wind Atlas mesoscale model output. We compare vertical profiles of wind speed, wind direction, momentum fluxes, and β up to 500 m, hence covering the rotor areas of modern offshore wind turbines and beyond. The results show that β ≈ −18° on average, with a lower, but still non-zero, value under stable stability conditions, ≈ −7°. We illustrate that the simulations describe well the mean wind speed and momentum fluxes within the observed levels, but the characterization of wind turning effects could be improved.

Wind flow and sediment flux profiles for vegetated surfaces in a wind tunnel and field-scale windbreak

Despite many studies describing wind speed and sediment flux profiles in various situations, wind tunnel observations in the presence of live vegetation are infrequent and rarely combined with field measurements. To investigate the structure of wind speed and sediment flux profiles in morphologically different vegetation and various plant densities, wind velocity and sediment flux profiles were obtained over a multi-row windbreak in an arid environment and over unplanted surfaces and canopies of two types of plants in a wind tunnel. Although the two plant types in the wind tunnel have different morphology, the profiles of wind velocity and sediment flux showed structures similar to those for other plant types reported in previous studies which indicates that profile structures are likely common for homogeneous canopies even with different plant morphology and in various wind velocities. The horizontal profiles of wind speed and vertical profiles of sediment flux in the wind tunnel closely matched the profiles in the field-scale windbreak. The vertical profiles of wind speed within the wind-tunnel vegetation exhibited a deflection which was not reflected within the multi-row windbreak where profiles were nearly uniform without inflections, which was likely a response to different plant spacing and patterns. Wind-tunnel vegetation reduced wind speed significantly even in low density. Lowest wind speeds were observed beyond the wind-tunnel canopies and at the beginning of the windbreak. No difference in the size of the sheltered zone is observed between the two plant types in the wind tunnel either in different wind velocities or in various density configurations, or within the windbreak in various wind speeds and different dust storm events. The sheltered area was greater for the windbreak than for the wind-tunnel canopies, suggesting that wind tunnel studies may under-estimate the sheltered area afforded by a multi-row windbreak.

Revisiting hurricane track model for wind risk assessment

Hurricane wind risk assessment has been significantly improved with the evolvement of synthesis methodologies from the single site probabilistic method to the hurricane track model (including five simulation components of genesis, translation, intensity, decay and boundary-layer wind). As first-step efforts towards advancing the data-driven hurricane track model, widely used by engineering community, to a physics-based framework for more accurate and reliable hurricane risk assessment, a new intensity model integrating important dynamics and thermodynamics inside the storms is developed. Furthermore, an extensive statistical analysis of hurricane trajectories is carried out to obtain an enhanced translation model and a height-resolving analytical wind model is utilized to acquire the vertical profiles of wind speed and direction between ground-surface and gradient levels. The other two simulation components (i.e., genesis and decay) of the hurricane track model are also revisited for the sake of completeness. Ten thousand years of full-track synthetic hurricanes are generated and compared with the HURDAT database at specific mileposts along the US East coast to validate the overall performance of the developed simulation framework (in terms of annual occurrence rate, intensity, translation speed and heading angle). Then, the New Jersey coastline is employed as a case study to compare the simulated hurricane wind speeds with ASCE 7–16 recommendations, to highlight the wind directionality effects on extreme wind speeds, and to investigate the joint distribution of hurricane wind speed and size.

Meteorological data recommendations for input to dispersion models applied to Jack Rabbit II trials

Abstract The Jack Rabbit II (JR II) chlorine field experiment observations are being used in a multi-dispersion model comparison exercise. So that all models are using consistent meteorological inputs, we analyzed the many early-morning meteorological observations that were taken at Dugway Proving Ground (DPG), Utah, during the nine chlorine release trials during JR II to produce recommendations for surface and vertical profile meteorological variables. The JR II field experiment included a mesonetwork of about 35 surface wind sites, a surface energy balance site, three 32 m towers located 1 km apart, and several vertical sounding instruments. The challenge is to determine a single set of meteorological inputs for the dispersion models. It is assumed that the recommended meteorological conditions represent the flat desert about 100 m upwind of the chlorine release location. Recommendations of surface winds, and momentum and sensible heat fluxes for each early-morning field trial are based on averages of sonic anemometer observations at 2 m on the upwind 32 m tower and at 2.5 m on a nearby “Energy Balance” station, for the half hour period during which the chlorine release took place. These observations were also used to estimate the surface roughness length, zo = 0.5 mm, for the flat desert. Single vertical profiles of wind speed, wind direction, and temperature are specified for each trial for a time close to the chlorine release time, based on medians of observations at five levels on the three 32 m towers, a radiosonde, a minisodar, and two wind profilers (449 MHz and 921 MHz). During the early morning releases, as the sun rose and heated the surface, the boundary layer was transient. The surface boundary layer was stable for releases from about 7:30 to about 8:30 (local time) and was marked by a shallow mixed layer (about 8–16 m) for releases during the next hour. Above the 32 m tower tops, the atmosphere was stable during all release trials up to elevations of a few hundred meters. Large wind direction shears were usually found in this layer, since the near-surface flow was a drainage (katabatic) down-valley flow (from about 165°), while the synoptic flow above 100 m was from the west.

Normal and typhoon wind loadings on a large cooling tower: A comparative study

Large cooling towers are sensitive to wind effects with their increasing heights and flexibilities. Unlike traditional approaches, which employed Code-defined normal winds to check the loading characteristics, this paper developed a framework for checking the typhoon-induced wind loading on a large cooling tower using Monte Carlo simulations and multi-fan wind tunnel tests. Some distinct characteristics of typhoon winds were compared with those of Code-defined normal winds. Furthermore, wind characteristics of incoming normal and typhoon winds in terms of vertical profile of mean wind speed, turbulence intensity, turbulence integral length scale and power spectrum density of fluctuating winds were well reproduced by a feedback control process of a multi-fan actively controlled wind tunnel. The surface wind pressure distributions of a large cooling tower under these conditions were then investigated by testing a 1:600 reduced scale model. Mean and fluctuating external wind pressures along the circumferential direction under various incoming winds were discussed and quantitatively formulated with eight-term trigonometric equations. Moreover, the cross correlations of wind pressures in the circumferential and meridian directions and correlations with structure base forces, i.e. integral drag and lift forces, were investigated. Non-Gaussian characteristics in terms of skewness and kurtosis of fluctuating wind pressures were also analyzed under two wind climates. Peak factors for modeling extreme wind pressures were examined and compared with those of various models. Finally, the extreme wind loads on a large cooling tower obtained from different wind pressure combinations were compared with peak-factor-theory-based results to identify an appropriate combination for structural design.

On the Analysis of the Performance of WRF and NICAM in a Hyperarid Environment

Abstract The Weather Research and Forecasting (WRF) Model and the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) are forced with the Global Forecast System (GFS) data and run over the United Arab Emirates (UAE) for two 4-day periods: one in the cold season (16–18 December 2017) and another in the warm season (13–15 April 2018). The models’ performance is evaluated against four observational datasets: weather station observations, eddy-covariance flux measurements at Al Ain, microwave radiometer–derived temperature profile, and twice-daily radiosonde measurements at Abu Dhabi. An overestimation of the daily mean air temperature by 1°–3°C is noticed for both models and periods. This warm bias is attributed to the reduced cloud cover and resulting increased surface downward shortwave radiation flux. A comparison with the eddy-covariance data suggested that both models also underestimate the observed albedo. However, when the models predict heavier amounts of precipitation, they tend to be colder than observations, typically by 2°–3°C. NICAM and WRF overpredict the strength of the near-surface wind speed at all weather stations by roughly 1–3 m s−1, which has been attributed to a poor representation of its subgrid-scale fluctuations and surface drag parameterization. WRF tends to be wetter and NICAM drier than the station observations, possibly because of differences in the cloud microphysics schemes. While the performance of both models for the near-surface fields is comparable, NICAM outperforms WRF in the simulation of vertical profiles of temperature, relative humidity, and wind speed, being able to partially correct some of the biases in the GFS data.