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Showing papers on "Wind shear published in 2020"


Journal ArticleDOI
01 Jun 2020
TL;DR: In this paper, the authors synthesize current knowledge on mesoscale convective system formation, climatological characteristics, hazardous weather, predictive capacity and projected changes with anthropogenic warming.
Abstract: Mesoscale convective systems (MCSs) describe organized groupings of thunderstorms in the tropics and mid-latitudes that span thousands of square kilometres. While recognized for over a century, the advent of satellite and radar observations, as well as atmospheric-model simulations, has brought about their increased understanding. In this Review, we synthesize current knowledge on MCS formation, climatological characteristics, hazardous weather, predictive capacity and projected changes with anthropogenic warming. Driven by typical deep moist convective processes (moisture, lift and instability) and vertical wind shear, MCS formation occurs preferentially in locations where these ingredients are present and can be maintained by large-scale ascent and the cold pools that they produce. MCSs also generate hazardous weather, including extreme rainfall, flooding, derechos and, sometimes, tornadoes and hail, all of which have substantial economic and societal impacts. Given that MCSs also produce a large fraction of warm-season rainfall, there is critical need for both short-term forecasts and long-term projections, presently challenged by inadequate model resolution. Yet, with continually improving modelling capabilities, as well as greater theoretical basis, it is suggested that MCSs might increase in frequency and intensity under a warming climate. Further modelling progress, in turn, offers improved understanding of MCS characteristics, from their life cycle through to impacts. Mesoscale convective systems are an important source of precipitation in many tropical and mid-latitude regions, but can also produce hazardous weather, such as extreme rain, derechos and tornadoes. This Review discusses the formation of mesoscale convective systems, their hazardous weather, predictive capabilities and projected changes with anthropogenic warming.

92 citations


Journal ArticleDOI
TL;DR: An open-source model which can generate the power curve of any turbine, adapted to the specific conditions of any site, is developed and validated against the manufacturer power curves of 91 turbine models.

58 citations


Journal ArticleDOI
TL;DR: Wang et al. as mentioned in this paper proposed a three-dimensional Jensen-Gaussian (3DJG) wake model for horizontal-axis wind turbines, which does not need multiple trial calculations to determine some empirical parameters, such as the wake expansion rate.

56 citations


Journal ArticleDOI
TL;DR: It is argued here that not only the wind speed in the vertical but the VWS were important for the investigation of aerosol pollution formation mechanism in Beijing and offer wider insights into the role of VWS from RWP in modulating the variation of PM2.5.
Abstract: Vertical wind shear (VWS) is one of the key meteorological factors in modulating ground-level particulate matter with an aerodynamic diameter of 2.5 µm or less (PM2.5). Due to the lack of high-resolution vertical wind measurements, how the VWS affects ground-level PM2.5 remains highly debated. Here we employed the wind profiling observations from the fine-time-resolution radar wind profiler (RWP), together with hourly ground-level PM2.5 measurements, to explore the wind features in the planetary boundary layer (PBL) and their association with aerosols in Beijing for the period from December 1, 2018, to February 28, 2019. Overall, southerly wind anomalies almost dominated throughout the whole PBL or even beyond the PBL under polluted conditions during the course of a day, as totally opposed to the northerly wind anomalies in the PBL under clean conditions. Besides, the ground-level PM2.5 pollution exhibited a strong dependence on the VWS. A much weaker VWS was observed in the lower part of the PBL under polluted conditions, compared with that under clean conditions, which could be due to the strong ground-level PM2.5 accumulation induced by weak vertical mixing in the PBL. Notably, weak northbound transboundary PM2.5 pollution mainly appeared within the PBL, where relatively small VWS dominated. Above the PBL, strong northerlies winds also favored the long-range transport of aerosols, which in turn deteriorated the air quality in Beijing as well. This was well corroborated by the synoptic-scale circulation and backward trajectory analysis. Therefore, we argued here that not only the wind speed in the vertical but the VWS were important for the investigation of aerosol pollution formation mechanism in Beijing. Also, our findings offer wider insights into the role of VWS from RWP in modulating the variation of PM2.5, which deserves explicit consideration in the forecast of air quality in the future.

50 citations


Journal ArticleDOI
01 Jan 2020-Energy
TL;DR: In this paper, a robust machine learning methodology is used to generate a site-specific power-curve of a full-scale isolated wind turbine operating in an atmospheric boundary layer to drastically improve the power predictions, and, thus, the forecasting of the monthly energy production estimates.

49 citations



Journal ArticleDOI
TL;DR: In this paper, the authors used the first convection-permitting simulations of African climate change to understand how changes in thermodynamics and storm dynamics affect future extreme Sahelian rainfall.
Abstract: Extreme rainfall is expected to increase under climate change, carrying potential socioeconomic risks. However, the magnitude of increase is uncertain. Over recent decades, extreme storms over the West African Sahel have increased in frequency, with increased vertical wind shear shown to be a cause. Drier midlevels, stronger cold pools, and increased storm organization have also been observed. Global models do not capture the potential effects of lower- to midtropospheric wind shear or cold pools on storm organization since they parameterize convection. Here we use the first convection-permitting simulations of African climate change to understand how changes in thermodynamics and storm dynamics affect future extreme Sahelian rainfall. The model, which simulates warming associated with representative concentration pathway 8.5 (RCP8.5) until the end of the twenty-first century, projects a 28% increase of the extreme rain rate of MCSs. The Sahel moisture change on average follows Clausius–Clapeyron scaling, but has regional heterogeneity. Rain rates scale with the product of time-of-storm total column water (TCW) and in-storm vertical velocity. Additionally, prestorm wind shear and convective available potential energy both modulate in-storm vertical velocity. Although wind shear affects cloud-top temperatures within our model, it has no direct correlation with precipitation rates. In our model, projected future increase in TCW is the primary explanation for increased rain rates. Finally, although colder cold pools are modeled in the future climate, we see no significant change in near-surface winds, highlighting avenues for future research on convection-permitting modeling of storm dynamics.

38 citations


Journal ArticleDOI
TL;DR: In this paper, an aeroelastic model based on the geometrically exact beam theory and blade element momentum method is established for wind turbine blades and the results show that the WS causes remarkable fluctuations of the flap deflection and yaw moment.

38 citations


Journal ArticleDOI
20 Jan 2020
TL;DR: In this article, the authors explore how the change in wind direction with height (direction wind shear), a site-differing factor between conflicting studies, and speed shear affect wind turbine performance.
Abstract: . Numerous studies have shown that atmospheric conditions affect wind turbine performance; however, some findings have exposed conflicting results for different locations and diverse analysis methodologies. In this study, we explore how the change in wind direction with height (direction wind shear), a site-differing factor between conflicting studies, and speed shear affect wind turbine performance. We utilized lidar and turbine data collected from the 2013 Crop Wind Energy eXperiment (CWEX) project between June and September in a wind farm in north-central Iowa. Wind direction and speed shear were found to follow a diurnal cycle; however, they evolved differently with increasing wind speeds. Using a combination of speed and direction shear values, we found large direction and small speed shear to result in underperformance. We further analyzed the effects of wind veering on turbine performance for specific values of speed shear and found detrimental conditions on the order of 10 % for wind speed regimes predominantly located in the middle of the power curve. Focusing on a time period of ramping electricity demand (06:00–09:00 LT – local time) exposed the fact that large direction shear occurred during this time and undermined turbine performance by more than 10 %. A predominance of clockwise direction shear (wind veering) cases compared to counterclockwise (wind backing) was also observed throughout the campaign. Moreover, large veering was found to have greater detrimental effects on turbine performance compared to small backing values. This study shows that changes in wind direction with height should be considered when analyzing turbine performance.

32 citations


Journal ArticleDOI
TL;DR: In this article, the combined effect of the anomalous stationary Rossby waves within two westerly jet waveguides on this haze event in the North China Plain (NCP) is investigated.
Abstract: . Severe haze occurred in the North China Plain (NCP) from November to December 2015, with a wide spatial range and long duration. In this paper, the combined effect of the anomalous stationary Rossby waves within two westerly jet waveguides on this haze event in the NCP is investigated based on observational visibility data and NCEP/NCAR reanalysis data. The results show that circulation anomalies in Eurasia caused by the propagation of anomalous stationary Rossby wave energy along two waveguides within the westerly jet originating from the Mediterranean were responsible for haze formation in the NCP. The Rossby waves propagated eastward along the subtropical westerly jet and the polar front jet, causing an anomalous anticyclone over the Sea of Japan and anticyclonic wind shear at 850 hPa over the NCP, which enhanced the anomalous descent in the middle and lower troposphere and subsequently resulted in a stable lower atmosphere. Furthermore, the anomalous stationary Rossby waves propagating along the polar front jet weakened the East Asia trough and Ural ridge and strengthened the anomalous southerly wind at 850 hPa over the coastal areas of eastern China, decelerating the East Asia winter monsoon. The above meteorological conditions modulated haze accumulation in November and December 2015. Meanwhile, continuous rainfall related to ascending motion due to Rossby wave propagation along the waveguide provided by the subtropical westerly jet occurred in a large area of southern China. The associated latent heat release acted as a heat source, intensifying the ascending motion over southern China so that the descending motion over the NCP was strengthened, favoring the maintenance of severe haze. This study elucidates the formation and maintenance mechanism of large-scale haze in the NCP in late fall and boreal winter.

32 citations


Journal ArticleDOI
TL;DR: In this article, the authors used ERA5 reanalysis and a 40-year timeframe (1979-2018) to construct the European climatology of environmental proxies associated with hazardous weather conditions causing disruptions in airline traffic.
Abstract: The consistently growing demand for airline transportation has resulted in increased air traffic and air operations in airports across the world. According to the International Air Transport Association, forecasts assume that in the year 2036 about 7.8 billion passengers will travel using air transport. In Europe, it is estimated that 16.2 million flights will take place in 2040, 53% more than in 2017. One of the crucial factors that significantly affect air transportation is the weather. In this article, ERA5 reanalysis and a 40-year timeframe (1979–2018) are used to construct the European climatology of environmental proxies associated with hazardous weather conditions causing disruptions in airline traffic. These include situations with limited visibility, thunderstorm, low-level wind shear, and snowfall. Results indicate that northern Europe and mountain zones are the most often affected by unfavorable weather conditions, while southern Europe is the least affected. Winter has the highest estimated number of situations with low-level wind shear and snowfall conditions. Situations with limited visibility are the most frequent in autumn and winter while thunderstorms are the main threat during summer over continental Europe and autumn in the Mediterranean area. Long-term changes of the analyzed proxies indicate that situations with low-level wind shear and snowfall are becoming less frequent while the number of thunderstorms generally increases, particularly over northern, central and south-central Europe. A decrease of situations with limited visibility is observed over majority of Europe with the exception of Scandinavia and parts of central Europe.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluate the skill of three relatively new wind atlases, i.e. ERA-5, DOWA and NEWA, on the representation of extreme wind events using observations taken at the Met Mast IJmuiden over the North Sea.
Abstract: Offshore wind energy production is rapidly growing as an essential element in the sustainable energy share. Wind energy siting studies require accurate wind data, and in particular the knowledge of extreme wind events (low-level jets, wind ramps, extreme shear and high wind speeds) is crucial for resource and load assessment. This study evaluates the skill of three relatively new wind atlases, i.e. ERA-5, DOWA and NEWA on the representation of extreme wind events using observations taken at the Met Mast IJmuiden over the North Sea. Overall, DOWA appears to best represent the wind speed profile with virtually no bias. ERA-5 underestimates the mean wind speed profile though the wind shear is well represented, while NEWA correctly represents the near surface wind but underestimates the wind shear. The frequency of low-level jets are also best represented by DOWA. Wind speed ramps and direction ramps are best represented by ERA-5, while DOWA appears to outperform the others concerning wind shear.

Journal ArticleDOI
TL;DR: In this article, the authors describe low-level wind shear as a known aviation safety hazard and refers to a sustained change in head wind encountered by an aircraft during takeoff or landing.
Abstract: “Low-level wind shear” is a known aviation safety hazard and refers to a sustained change in head wind encountered by an aircraft during takeoff or landing. Because of their small spatiotem...

Journal ArticleDOI
TL;DR: A flexible dynamic model of the drive train is presented, which includes not only the full coupling of gear meshing but also the flexibilities of planet carrier and ring gear, and shows that resonant peaks of the system are more likely to appear when the mesh frequency or its multiplication of the gear pair 1–2 is equal to the natural frequency.

Journal ArticleDOI
11 Sep 2020
TL;DR: In this paper, the sensitivity of a wind turbine's power production to wind speed shear and directional veer as well as atmospheric stability was quantified using observed winds and power production over 6 months at a site in the high plains of North America.
Abstract: . Most megawatt-scale wind turbines align themselves into the wind as defined by the wind speed at or near the center of the rotor (hub height). However, both wind speed and wind direction can change with height across the area swept by the turbine blades. A turbine aligned to hub-height winds might experience suboptimal or superoptimal power production, depending on the changes in the vertical profile of wind, also known as shear. Using observed winds and power production over 6 months at a site in the high plains of North America, we quantify the sensitivity of a wind turbine's power production to wind speed shear and directional veer as well as atmospheric stability. We measure shear using metrics such as α (the log-law wind shear exponent), βbulk (a measure of bulk rotor-disk-layer veer), βtotal (a measure of total rotor-disk-layer veer), and rotor-equivalent wind speed (REWS; a measure of actual momentum encountered by the turbine by accounting for shear). We also consider the REWS with the inclusion of directional veer, REWSθ , although statistically significant differences in power production do not occur between REWS and REWSθ at our site. When REWS differs from the hub-height wind speed (as measured by either the lidar or a transfer function-corrected nacelle anemometer), the turbine power generation also differs from the mean power curve in a statistically significant way. This change in power can be more than 70 kW or up to 5 % of the rated power for a single 1.5 MW utility-scale turbine. Over a theoretical 100-turbine wind farm, these changes could lead to instantaneous power prediction gains or losses equivalent to the addition or loss of multiple utility-scale turbines. At this site, REWS is the most useful metric for segregating the turbine's power curve into high and low cases of power production when compared to the other shear or stability metrics. Therefore, REWS enables improved forecasts of power production.

Journal ArticleDOI
TL;DR: In this article, the authors examined the possibility that storm-relative helicity (SRH) integrated over progressively shallower layers has increased skill in differentiating between significantly tornadic and nontornadic severe thunderstorms.
Abstract: The near-ground wind profile exhibits significant control over the organization, intensity, and steadiness of low-level updrafts and mesocyclones in severe thunderstorms, and thus their probability of being associated with tornadogenesis. The present work builds upon recent improvements in supercell tornado forecasting by examining the possibility that storm-relative helicity (SRH) integrated over progressively shallower layers has increased skill in differentiating between significantly tornadic and nontornadic severe thunderstorms. For a population of severe thunderstorms in the United States and Europe, sounding-derived parameters are computed from the ERA5 reanalysis, which has significantly enhanced vertical resolution compared to prior analyses. The ERA5 is shown to represent U.S. convective environments similarly to the Storm Prediction Center’s mesoscale surface objective analysis, but its greater number of vertical levels in the lower troposphere permits calculations to be performed over shallower layers. In the ERA5, progressively shallower layers of SRH provide greater discrimination between nontornadic and significantly tornadic thunderstorms in both the United States and Europe. In the United States, the 0–100 m AGL layer has the highest forecast skill of any SRH layer tested, although gains are comparatively modest for layers shallower than 0–500 m AGL. In Europe, the benefit from using shallower layers of SRH is even greater; the lower-tropospheric SRH is by far the most skillful ingredient there, far exceeding related composite parameters like the significant tornado parameter (which has negligible skill in Europe).

Journal ArticleDOI
TL;DR: In this article, a persistent pollution case during 6 December 2016-8 January 2017 was selected to investigate the relations between turbulent intermittency and frequent PM2.5 (particulate matters with diameter less than 2.5 μm) pollution events over the metropolitan region of Beijing, China.
Abstract: With rapid urbanization in recent years, severe air pollution has emerged as a major issue for many regions of China, especially in some metropolises. A persistent pollution case during 6 December 2016–8 January 2017 was selected to investigate the relations between turbulent intermittency and frequent PM2.5 (particulate matters with diameter less than 2.5 μm) pollution events over the metropolitan region of Beijing, China. The accumulation of PM2.5 near the surface frequently occurred as a combined result of strong inversion layers, stagnant winds, high ambient humidity levels, and stable stratification during this case. Arbitrary-order Hilbert spectral analysis indicated that steep decreases in the PM2.5 concentration were simultaneous with the occurrence of intermittent turbulence and strong vertical mixing. A wind profiler observation revealed existence of low-level jets (LLJs) at the end of the polluted periods, suggesting that the upper-level turbulent mixing accompanied by the wind shear of LLJ was transported downward and enhanced the vertical mixing near the surface, which might have caused an abrupt reduction in PM2.5 and improvement in air conditions.

Journal ArticleDOI
TL;DR: The secondary circulation over the Sichuan Basin is weaker on cloudy days than on sunny days, although the contribution of the sensible heat flux to hmax is less than that of the wind shear, which is important for understanding the dispersion of air pollutants.

Journal ArticleDOI
TL;DR: In this article, the authors used 8 years of floating chamber measurements from three small, shallow subarctic lakes (2010-2017, n=1306 ) to separate the contribution of physically and biogeochemical processes to the turbulence-driven, diffusion-limited flux of methane (CH4 ) on daily to multi-year timescales.
Abstract: . Lakes and reservoirs contribute to regional carbon budgets via significant emissions of climate forcing trace gases. Here, for improved modelling, we use 8 years of floating chamber measurements from three small, shallow subarctic lakes (2010–2017, n=1306 ) to separate the contribution of physical and biogeochemical processes to the turbulence-driven, diffusion-limited flux of methane ( CH4 ) on daily to multi-year timescales. Correlative data include surface water concentration measurements (2009–2017, n=606 ), total water column storage (2010–2017, n=237 ), and in situ meteorological observations. We used the last to compute near-surface turbulence based on similarity scaling and then applied the surface renewal model to compute gas transfer velocities. Chamber fluxes averaged 6.9±0.3 mg CH4 m −2 d −1 and gas transfer velocities ( k600 ) averaged 4.0±0.1 cm h −1 . Chamber-derived gas transfer velocities tracked the power-law wind speed relation of the model. Coefficients for the model and dissipation rates depended on shear production of turbulence, atmospheric stability, and exposure to wind. Fluxes increased with wind speed until daily average values exceeded 6.5 m s −1 , at which point emissions were suppressed due to rapid water column degassing reducing the water–air concentration gradient. Arrhenius-type temperature functions of the CH4 flux ( E a ′ = 0.90 ± 0.14 eV) were robust ( R2≥0.93 , p ) and also applied to the surface CH4 concentration ( E a ′ = 0.88 ± 0.09 eV). These results imply that emissions were strongly coupled to production and supply to the water column. Spectral analysis indicated that on timescales shorter than a month, emissions were driven by wind shear whereas on longer timescales variations in water temperature governed the flux. Long-term monitoring efforts are essential to identify distinct functional relations that govern flux variability on timescales of weather and climate change.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the behavior of the near-surface wind shear velocity in the presence of aeolian sand fences and show that the area of soil associated with values of near surface wind velocity that are below the minimal threshold for sand transport has two regimes, depending on the spacing L x between the fences.

Journal ArticleDOI
TL;DR: In this article, a partial repowering strategy has been discussed for an onshore commercial-scale wind farm with deteriorated performance under the influence of wakes originating from upstream wind farms.



Journal ArticleDOI
TL;DR: In this article, the authors derived a formula for the maximum updraft w that incorporates the effects of entrainment-driven dilution on buoyancy but neglects pressure gradient forces.
Abstract: In supercell environments, previous authors have shown strong connections between the vertical wind shear magnitude, updraft width, and entrainment Based on these results, it is hypothesized that the influences of entrainment-driven dilution on buoyancy and maximum updraft vertical velocity w in supercell environments are a predictable function of the vertical wind shear profile It is also hypothesized that the influences of pressure perturbation forces on maximum updraft w are small because of a nearly complete offset between upward dynamic pressure forces and downward buoyant pressure forces To address these hypotheses, we derive a formula for the maximum updraft w that incorporates the effects of entrainment-driven dilution on buoyancy but neglects pressure gradient forces Solutions to this formula are compared with output from previous numerical simulations This formula substantially improves predictions of maximum updraft w over past CAPE-derived formulas for maximum updraft w , which supports the first hypothesis Furthermore, integrated vertical accelerations along trajectories show substantial offsets between dynamic and buoyant pressure forces, supporting the second hypothesis It is argued that the new formula should be used in addition to CAPE-derived measures for w in forecast and research applications when accurate diagnosis of updraft speed is required

Journal ArticleDOI
20 Mar 2020
TL;DR: In this article, the role of the vertical wind shear in the lower and middle troposphere, in terms of low-level shear and deep level shear, and of the convective available potential energy (CAPE) as possible precursors of significant tornadoes is statistically investigated.
Abstract: In this study, mesoscale environments associated with 57 significant tornadoes occurring over Italy in the period 2000–2018 are analyzed. The role of the vertical Wind Shear in the lower and middle troposphere, in terms of low-level shear (LLS) and deep-level shear (DLS), and of the convective available potential energy (CAPE) as possible precursors of significant tornadoes is statistically investigated. Wind shear and CAPE data are extracted from the ERA-5 and ERA-Interim reanalyses. Overall, the study indicates that: (a) values of these variables in the two uppermost quartiles of their statistical distribution significantly increases the probability of tornado occurrences; (b) the probability increases for increasing values of LLS and DLS, and (c) is maximum when either wind shear or CAPE are large. These conclusions hold for both the reanalysis datasets and do not depend upon the season and/or the considered area. With the possible exception of weak tornadoes, which are not included in our study, our results show that large wind shear, in the presence of medium-to-high values of CAPE, are reliable precursors of tornadoes.

Journal ArticleDOI
17 Jul 2020
TL;DR: In this article, the authors found that more than 50% of lightning strikes can be linked to a nearby cut-off low or positive potential vorticity (PV) filament.
Abstract: . Over three weeks in May and June 2018, an exceptionally large number of thunderstorms hit vast parts of western and central Europe, causing precipitation of up to 80 mm and several flash floods. During this time, the large-scale atmospheric circulation, which was characterized by a blocking situation over northern Europe, influenced atmospheric conditions relevant for thunderstorm development. Initially, the southwesterly flow on the western flank of the blocking anticyclone induced the advection of warm, moist, and unstably stratified air masses. Due to a low-pressure gradient associated with the blocking anticyclone, these air masses were trapped in western and central Europe, remained almost stationary and prevented a significant air mass exchange. In addition, the low-pressure gradient led to weak flow conditions in the mid-troposphere and thus to low vertical wind shear that prevented thunderstorms from developing into severe organized systems. Most of the storms formed as local-scale, relatively slow-moving single cells. However, due to the related weak propagation speed, several thunderstorms were able to produce torrential heavy rain that affected local-scale areas and triggered several flash floods. Atmospheric blocking also increased the upper-level cut-off low frequency on its upstream regions, which was up to 10 times higher than the climatological mean. Together with filaments of positive potential vorticity (PV), the cut-offs served as trigger mechanisms for a majority of the thunderstorms. For the 22-day study period, we found that more than 50 % of lightning strikes can be linked to a nearby cut-off low or PV filament. The exceptional persistence of low stability combined with weak wind speed in the mid-troposphere over three weeks has not been observed during the past 30 years.

Journal ArticleDOI
TL;DR: In this article, numerical simulations of weak tropical cyclones (e.g., tropical depressions and tropical storms) in sheared environments indicate that vortex tilt reduction and convective symmetr...
Abstract: Idealized numerical simulations of weak tropical cyclones (e.g., tropical depressions and tropical storms) in sheared environments indicate that vortex tilt reduction and convective symmetr...

Journal ArticleDOI
TL;DR: The results reveal that cloud radiative cooling was the main source of downdraft, which was also confirmed by the detailed case study of vertical velocity, and provide useful references for local weather forecast and air quality studies.
Abstract: Turbulent mixing is critical in affecting urban climate and air pollution. Nevertheless, our understanding of it, especially in a cloud-topped boundary layer (CTBL), remains limited. High-temporal resolution observations provide sufficient information of vertical velocity profiles, which is essential for turbulence studies in the atmospheric boundary layer (ABL). We conducted Doppler Light Detection and Ranging (LiDAR) measurements in 2019 using the 3-Dimensional Real-time Atmospheric Monitoring System (3DREAMS) to reveal the characteristics of typical daytime turbulent mixing processes in CTBL over Hong Kong. We assessed the contribution of cloud radiative cooling on turbulent mixing and determined the altitudinal dependence of the contribution of surface heating and vertical wind shear to turbulent mixing. Our results show that more downdrafts and updrafts in spring and autumn were observed and positively associated with seasonal cloud fraction. These results reveal that cloud radiative cooling was the main source of downdraft, which was also confirmed by our detailed case study of vertical velocity. Compared to winter and autumn, cloud base heights were lower in spring and summer. Cloud radiative cooling contributed ~32% to turbulent mixing even near the surface, although the contribution was relatively weaker compared to surface heating and vertical wind shear. Surface heating and vertical wind shear together contributed to ~45% of turbulent mixing near the surface, but wind shear can affect up to ~1100 m while surface heating can only reach ~450 m. Despite the fact that more research is still needed to further understand the processes, our findings provide useful references for local weather forecast and air quality studies.

Journal ArticleDOI
15 Feb 2020-Energy
TL;DR: In this article, the performance of AWE systems relative to traditional wind power turbines (WT) is compared to the hourly power production of classical WTs, and the results show that AWE system with multiple smaller wings have the highest annual production.

Journal ArticleDOI
TL;DR: In this paper, wind characteristics in different regimes occurring throughout the idealized diurnal cycle and its impact on wind turbine's power performance are investigated systematically by means of large-eddy simulation (LES), and blade element momentum method (BEM), respectively.