scholarly journals Assessment of nocturnal low-level jets during the FESSTVaL campaign 2020 for wind energy applications

2021 ◽  
Author(s):  
Eduardo Weide Luiz ◽  
Stephanie Fiedler
Keyword(s):  
Wind Power ◽  
Wind Turbines ◽  
Vertical Wind Shear ◽  
Ground Level ◽  
High Temporal Resolution ◽  
Missing Measurements ◽  
Low Level ◽  
Prevailing Wind Direction ◽  
Meteorological Observatory ◽  
Low Level Jets

<p>Due to the increasing contribution of wind power to electricity in Europe, an exact wind characterization at the height of wind turbines is important. Nocturnal Low Level Jets (NLLJ) can influence the winds at typical blade heights and therefore influence the wind power production. However, due to the often missing measurements with a sufficient precision and resolution, the occurrence frequency and spatio-temporal characteristics of NLLJs are still poorly understood. The present work characterizes the properties of NLLJs, measured with a Doppler lidar at the Lindenberg Meteorological Observatory – Richard Aßmann Observatory (Germany), during the period of June–August 2020, and evaluates the representation of NLLJs in state-of-the-science re-analysis products. The vertical profiles of 10-minute mean winds from the lidar are statistically analysed using automated detection tools. These allow to determine the frequency of occurrence, height and wind speed in the core of NLLJs as well as the vertical wind shear and momentum transport with a high temporal resolution. We intercompare NLLJ results from different previously-used identification tools to estimate the uncertainty. Our automatic detections identified NLLJs in more than about 60% of the summer nights in 2020, with NLLJ cores between 70m and 500 m above ground level and a core speed of ~3–25 m/s. The prevailing wind direction in NLLJ cores is southwest. A considerable amount of NLLJ cores occurred at heights that are in the range of modern wind turbines and rotor sizes on land, with wind speeds of ~3-12 m/s. We use the measurements of NLLJs to evaluate their representation in the ERA5 re-analysis of the European Centre for Medium-Range Weather Forecasts and plan to compare the NLLJs to regional high-resolution re-analyses developed in the research area Climate Monitoring and Diagnostics in the Hans-Ertel Centre for Weather Research.  The first comparisons suggest a frequent co-occurrence of NLLJs in the measurements and ERA5 re-analysis, but the strength and height of NLLJ cores often differ. Possible reasons are the model’s vertical resolution and the parameterization of vertical mixing in the stable boundary layer. Future work includes extending the NLLJ analysis to more lidar measurements and other regional re-analysis data.</p>

scholarly journals Sensitivity of nocturnal low-level jets to land-use parameters and meteorological quantities

2019 ◽  
Vol 16 ◽  
pp. 85-93 ◽  
Author(s):  
Astrid Ziemann ◽  
Manuela Starke ◽  
Tina Leiding
Keyword(s):  
Land Use ◽  
Wind Speed ◽  
Wind Power ◽  
Wind Turbines ◽  
Geostrophic Wind ◽  
Scale Model ◽  
Model Parameters ◽  
Height Range ◽  
Low Level ◽  
Low Level Jets

Abstract. The increasing hub height of wind turbines aims at optimizing the wind energy yield at one location and offers the possibility to provide new areas for wind power, for example forests. Inhomogeneous environmental conditions of locations for wind turbines as well as the hub heights of more than 100 m cause challenges for flow models and their potential for wind power assessment. This includes special features of the wind field like low-level jets (LLJs), frequently observed local wind maxima in the nocturnal boundary layer. To characterize the dependencies of LLJs, the micro-scale model HIRVAC2D (HIgh Resolution Vegetation Atmosphere Coupler 2D) is applied in the study. The model HIRVAC2D is capable of modelling different vegetation types by explicitly considering the highly resolved structure of varying plant parameters. Beyond that, the model enables the resolution of temporally variable atmospheric circulation patterns during day- and night-time with typical thermal stratifications. In this way, HIRVAC2D is suitable to capture the nocturnal LLJ development and its characteristics. Results of several HIRVAC2D simulations are presented in order to deduce quantitatively the sensitivity of LLJs to vegetation and model parameters as well as meteorological quantities. It is shown that the geostrophic wind speed is an important criterion for the development of LLJs within a height range between 50 and 300 m. For a geostrophic wind speed of 4 m s−1, a nocturnal LLJ occurs remarkably more frequent as for a wind speed of 10 m s−1. To interpret and evaluate this result regarding possible wind power applications, a frequency distribution of the geostrophic wind speed was calculated over 30 years exemplarily at two locations using the meso-scale model COSMO in climate mode. Additionally, the type of land use has an impact on the height and intensity of LLJs. For a grassland site, the nocturnal LLJ is noticeably more frequent in the considered height range, but with a smaller wind speed and at a lower height above ground in comparison to deciduous or coniferous forests.

scholarly journals A Climatology of Nocturnal Low-Level Jets at Cabauw

2009 ◽  
Vol 48 (8) ◽  
pp. 1627-1642 ◽  
Author(s):  
P. Baas ◽  
F. C. Bosveld ◽  
H. Klein Baltink ◽  
A. A. M. Holtslag
Keyword(s):  
Wind Speed ◽  
Ground Level ◽  
Geostrophic Wind ◽  
Stable Stratification ◽  
Radiative Cooling ◽  
Inertial Oscillation ◽  
Stable Boundary Layers ◽  
Above Ground Level ◽  
Low Level ◽  
Low Level Jets

Abstract A climatology of nocturnal low-level jets (LLJs) is presented for the topographically flat measurement site at Cabauw, the Netherlands. LLJ characteristics are derived from a 7-yr half-hourly database of wind speed profiles, obtained from the 200-m mast and a wind profiler. Many LLJs at Cabauw originate from an inertial oscillation, which develops after sunset in a layer decoupled from the surface by stable stratification. The data are classified to different types of stable boundary layers by using the geostrophic wind speed and the isothermal net radiative cooling as classification parameters. For each of these classes, LLJ characteristics like frequency of occurrence, height above ground level, and the turning of the wind vector across the boundary layer are determined. It is found that LLJs occur in about 20% of the nights, are typically situated at 140–260 m above ground level, and have a speed of 6–10 m s−1. Development of a substantial LLJ is most likely to occur for moderate geostrophic forcing and a high radiative cooling. A comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is added to illustrate how the results can be used to evaluate the performance of atmospheric models.

Wind conditions over the Baltic Sea – comparing reanalysis data sets with observations

2020 ◽  
Author(s):  
Christoffer Hallgren ◽  
Erik Sahlée ◽  
Stefan Ivanell ◽  
Heiner Körnich ◽  
Ville Vakkari
Keyword(s):  
Baltic Sea ◽  
Wind Power ◽  
Reanalysis Data ◽  
Data Sets ◽  
The Baltic Sea ◽  
Data Set ◽  
Low Level ◽  
Seasonal And Diurnal Variations ◽  
Low Level Jets ◽  
The Baltic

<p>The potential of increasing the amount of offshore wind energy production in the Baltic Sea has been of great interest for many countries and wind power companies for a long time. From a meteorological point of view, there are several special wind characteristics that are observed in this area that needs to be taken into consideration when planning for a wind farm. For example, as the Baltic Sea is a semi-enclosed basin surrounded by coastlines in all directions, phenomenon such as low-level jets occur frequently.</p><p>In order to create a climatology of the wind conditions over the Baltic Sea, with wind power applications in mind, four different state-of-the-art reanalysis data sets (MERRA2, ERA5, UERRA and NEWA) have been compared with measurements from LIDAR systems and high meteorological towers (Anholt, Finnish Utö, FINO2 and Östergarnsholm). The performance of the data sets has been analyzed in terms of stability and governing synoptic weather conditions as well as seasonal and diurnal variations. By selecting the most suitable reanalysis data set and using the observations to make corrections, a climatology for wind conditions over the Baltic Sea, focusing on the low-level jets, has then been constructed.</p>

Structural impact assessment of low level jets over wind turbines

2016 ◽  
Vol 8 (2) ◽  
pp. 023308 ◽  
Author(s):  
W. Gutierrez ◽  
G. Araya ◽  
P. Kiliyanpilakkil ◽  
A. Ruiz-Columbie ◽  
M. Tutkun ◽  
...  
Keyword(s):  
Impact Assessment ◽  
Wind Turbines ◽  
Low Level ◽  
Structural Impact ◽  
Low Level Jets

scholarly journals Low-Level Jets over Utö, Finland, Based on Doppler Lidar Observations

2017 ◽  
Vol 56 (9) ◽  
pp. 2577-2594 ◽  
Author(s):  
Minttu Tuononen ◽  
Ewan J. O’Connor ◽  
Victoria A. Sinclair ◽  
Ville Vakkari
Keyword(s):  
Sonic Anemometer ◽  
Ground Level ◽  
Small Island ◽  
Lidar Data ◽  
Identification Algorithm ◽  
Frequency Of Occurrence ◽  
Doppler Lidar ◽  
Low Level ◽  
Low Level Jets ◽  
The Baltic

AbstractOver two years of meteorological observations from Utö, a small island in the Finnish outer archipelago in the Baltic Sea, were used to investigate the occurrence and characteristics of low-level jets (LLJs) and the diurnal and seasonal variations in these properties. An objective LLJ identification algorithm that is suitable for high-temporal-and-vertical-resolution Doppler lidar data was created and applied to wind profiles obtained from a combination of Doppler lidar data and two-dimensional sonic anemometer observations. This algorithm was designed to identify coherent LLJ structures and requires that they persist for at least 1 h. The long-term mean LLJ frequency of occurrence at Utö was 12%, the mean LLJ wind speed was 11.6 m s−1, and the vast majority of identified LLJs occurred below 150 m above ground level. The LLJ frequency of occurrence was much higher during summer (21%) and spring (18%) than in autumn (8%) and winter (3%). During winter and spring, the LLJ frequency of occurrence is evenly distributed throughout the day. In contrast, the LLJ frequency of occurrence peaks at night (1900–0100 UTC) during summer and during the evening hours (1700–1900 UTC) in autumn. The highest and strongest LLJs come from the southwest, which is also the predominant LLJ direction in all seasons. LLJs below 100 m are common in spring and summer, are weaker, and do not show a strong directional dependence.

scholarly journals Doppler Radar Analysis of a Tornadic Miniature Supercell during the Landfall of Typhoon Mujigae (2015) in South China

2017 ◽  
Vol 98 (9) ◽  
pp. 1821-1831 ◽  
Author(s):  
Kun Zhao ◽  
Mingjun Wang ◽  
Ming Xue ◽  
Peiling Fu ◽  
Zhonglin Yang ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Vertical Direction ◽  
Ground Level ◽  
Large Cell ◽  
Small Surface ◽  
Low Level ◽  
Wind Analysis ◽  
Lifting Condensation Level

Abstract On 4 October 2015, a miniature supercell embedded in an outer rainband of Typhoon Mujigae produced a major tornado in Guangdong province of China, leading to 4 deaths and up to 80 injuries. This study documents the structure and evolution of the tornadic miniature supercell using coastal Doppler radars, a sounding, videos, and a damage survey. This tornado is rated at least EF3 on the enhanced Fujita scale. It is by far the strongest typhoon rainband tornado yet documented in China, and possessed double funnels near its peak intensity. Radar analysis indicates that this tornadic miniature supercell exhibited characteristics similar to those found in United States landfalling hurricanes, including a hook echo, low-level inf low notches, an echo top below 10 km, a small and shallow mesocyclone, and a long lifespan (3 h). The environmental conditions—which consisted of moderate convective available potential energy (CAPE), a low lifting condensation level, a small surface dewpoint depression, a large veering low-level vertical wind shear, and a large cell-relative helicity—are favorable for producing miniature supercells. The mesocyclone, with its maximum intensity at 2 km above ground level (AGL), formed an hour before tornadogenesis. A tornado vortex signature (TVS) was identified between 1 and 3 km AGL, when the parent mesocyclone reached its peak radar-indicated intensity of 30 m s−1. The TVS was located between the updraft and forward-flank downdraft, near the center of the mesocyclone. Dual-Doppler wind analysis reveals that tilting of the low-level vorticity into the vertical direction and subsequent stretching by a strong updraft were the main contributors to the mesocyclone intensification.

scholarly journals Observing and Simulating the Summertime Low-Level Jet in Central Iowa

2015 ◽  
Vol 143 (6) ◽  
pp. 2319-2336 ◽  
Author(s):  
Brian J. Vanderwende ◽  
Julie K. Lundquist ◽  
Michael E. Rhodes ◽  
Eugene S. Takle ◽  
Samantha L. Irvin
Keyword(s):  
Great Plains ◽  
Vertical Wind Shear ◽  
Ground Level ◽  
Turbine Rotor ◽  
Inertial Oscillation ◽  
Energy Forecasting ◽  
Site Assessment ◽  
Low Level ◽  
Low Level Jet ◽  
Wind Profiles

Abstract In the U.S. state of Iowa, the increase in wind power production has motivated interest into the impacts of low-level jets on turbine performance. In this study, two commercial lidar systems were used to sample wind profiles in August 2013. Jets were systematically detected and assigned an intensity rating from 0 (weak) to 3 (strong). Many similarities were found between observed jets and the well-studied Great Plains low-level jet in summer, including average jet heights between 300 and 500 m above ground level, a preference for southerly wind directions, and a nighttime bias for stronger jets. Strong vertical wind shear and veer were observed, as well as veering over time associated with the LLJs. Speed, shear, and veer increases extended into the turbine-rotor layer during intense jets. Ramp events, in which winds rapidly increase or decrease in the rotor layer, were also commonly observed during jet formation periods. The lidar data were also used to evaluate various configurations of the Weather Research and Forecasting Model. Jet occurrence exhibited a stronger dependence on the choice of initial and boundary condition data, while reproduction of the strongest jets was influenced more strongly by the choice of planetary boundary layer scheme. A decomposition of mean model winds suggested that the main forcing mechanism for observed jets was the inertial oscillation. These results have implications for wind energy forecasting and site assessment in the Midwest.

Exploring the effects of low-level-jets on the energy entrainment of vertical-axis wind turbines

2021 ◽  
Vol 13 (3) ◽  
pp. 033310
Author(s):  
Diego Siguenza-Alvarado ◽  
Ali Doosttalab ◽  
Shyuan Cheng ◽  
Humberto Bocanegra Evans ◽  
Raúl Bayoán Cal ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Vertical Axis ◽  
Low Level ◽  
Vertical Axis Wind Turbines ◽  
Low Level Jets

Modeling of the power generation from wind turbines with high spatial and temporal resolution

2020 ◽  
Author(s):  
Reinhold Lehneis ◽  
David Manske ◽  
Björn Schinkel ◽  
Daniela Thrän
Keyword(s):  
Numerical Simulation ◽  
Power Generation ◽  
Time Series ◽  
Wind Turbine ◽  
Wind Power ◽  
Temporal Resolution ◽  
Wind Turbines ◽  
Weather Data ◽  
Specific Power ◽  
High Temporal Resolution

<p>The share of wind power in the generation of electricity has increased significantly in recent years and, despite its volatility, variable energy from wind turbines has become an essential pillar for the power supply in many countries around the world. To investigate the effects of increasing variable renewables on power grids, the environment or electricity markets, detailed power generation data from wind turbines with high spatial and temporal resolution are often mandatory. The lack of freely accessible feed-in time series, for example due to data protection regulations, makes it necessary to determine the wind power feed-in for a required region and period with the help of numerical simulations. Our contribution demonstrates how such a numerical simulation can be developed using publicly available wind turbine and weather data. Herein, a novel model approach will be presented for the wind-to-power conversion, which utilizes a sixth-order polynomial for the specific power curve of a wind turbine. After such an analytical representation is derived for a certain turbine, its output power can be easily calculated using the wind speed and air temperature at its hub height. For proof of concept and model validation, measured feed-in time-series of a geographically and technically known wind turbine are compared with the simulated time-series at a high temporal resolution of 10 minutes. In order to determine the power generation for larger regions or an entire country the derived numerical simulation is also carried out for an ensemble of almost 26 thousand onshore wind turbines in Germany with a total capacity of about 44 GW. With this ensemble, first simulation results with municipal and hourly resolution can be presented for an annual period.</p>

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