Vertical wind shear

This study investigates the precipitation symmetrization preceding rapid intensification (RI) of tropical cyclones (TCs) experiencing vertical wind shear by analyzing numerical simulations of Typhoon Mujigae (2015) with warm (CTL) and relatively cool (S1) sea surface temperatures (SSTs). A novel finding is that precipitation symmetrization is maintained by the continuous development of deep convection along the inward flank of a convective precipitation shield (CPS), especially in the downwind part. Beneath the CPS, downdrafts flush the boundary layer with low-entropy parcels. These low-entropy parcels do not necessarily weaken the TCs; instead, they are “recycled” in the TC circulation, gradually recovered by positive enthalpy fluxes, and develop into convection during their propagation toward a downshear convergence zone. Along-trajectory vertical momentum budget analyses reveal the predominant role of buoyancy acceleration in the convective development in both experiments. The bo...

This study investigates the asymmetric structure of the hurricane boundary layer in relation to the environmental vertical wind shear in the inner core region. Data from 1878 GPS dropsondes deployed by research aircraft in 19 hurricanes are analyzed in a composite framework. Kinematic structure analyses based on Doppler radar data from 75 flights are compared with the dropsonde composites. Shear-relative quadrant-mean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to decrease with decreasing radius, consistent with previous axisymmetric analyses. There is still a clear separation between the kinematic and thermodynamic boundary layer heights. Both the thermodynamic mixed layer and height of maximum tangential wind speed are within the inflow layer. The inflow layer depth is found to be deeper in quadrants downshear, with the downshear right (DR) quadrant being the deepest. The mixed layer depth and height of maximum tangential win...

This paper presents a novel approach to the longitudinal guidance and control issue for an aircraft in presence of wind shear. The main contribution concerns the adaptive estimation of the wind shear disturbances affecting the aircraft and the development of a control scheme suitable to compensate these effects during a precision approach procedure. The work proposes the design, based on the Nonlinear Geometric Approach, of three adaptive filters providing the estimate of the wind shear disturbance components. These estimates are exploited, in an original way, by a BackStepping based controller, thus resulting in an Adaptive BackStepping Controller. Simulation results, obtained by means of a detailed flight simulator implementing the real wind shear condition which caused the 1975 crash of Eastern Flight 066 at JFK airport and a Montecarlo robustness test, demonstrates the effectiveness of the proposed method.

Complex noises sources are not easily measured when the conditions constantly change. Wind turbines are an example of these challenging sources. Some say it’s like magic; now you hear them and now you don’t. Sound comes and goes and changes with distance, temperature, humidity, wind speed, wind direction, wind shear, thermal inversion, sound absorption, etc. Its annoyance and detectability may also be masked by various forms of intermittent background noise. There is also unwanted noise inherent with the measurement system itself, such as wind screen noise that needs to be separated from the sources of interest. These need to be identified such that only clean records where artifacts are not present are chosen and the sources of interest are analyzed. Being variables, many may, at times, have a cumulative effect on the sources, increasing their presence.  Different receptors (humans and animals) react differently with different types of noise. Receptors that live under these conditi...

This paper is the third of a series that focuses on the applications of the ground-based velocity track display (GBVTD) technique and the GBVTD-simplex center finding algorithm developed in the previous two papers to a real tropical cyclone (TC). The evolution and structure of Typhoon Alex (1987), including full tangential winds, mean radial winds, one component of the mean flow, and their derived axisymmetric angular momentum and perturbation pressure fields are reconstructed from 16 volume scans (6.5 h of data with a 2-h gap) from the Civil Aeronautic Administration (CAA) Doppler radar while Typhoon Alex moved across the mountainous area in northern Taiwan. This analysis retrieves a plausible and physically consistent three-dimensional primary circulation of a landfalling TC using a single ground-based Doppler radar. Highly asymmetric wind structures were resolved by the GBVTD technique where the maximum relative tangential wind at z ϭ 2 km evolved from 52 m s Ϫ1 (before landfall), to less than 40 m s Ϫ1 (after landfall), to less than 35 m s Ϫ1 (entering the East China Sea). Alex's eye began to fill with precipitation while its intensity decreased rapidly after landfall, a characteristic of circulations disrupted by terrain. The mean radial wind field revealed a layer of low-level inflow in agreement with past TC observations. The outward slope of the eyewall reflectivity maximum was consistent with the constant angular momentum contours within the eyewall. After Alex entered the East China Sea, its circulation became more axisymmetric. The axisymmetric perturbation pressure field was retrieved using the gradient wind approximation, which, when used in conjunction with one or more surface pressure measurements within the analysis domain, can estimate the central pressure. The retrieved perturbation pressure fields at two time periods were compared with surface pressures reported in northern Taiwan. Considering the assumptions involved and the influence of terrain, good agreement (only 1-2-mb deviation) was found between them. This agreement indicates the relative quality of the GBVTD-retrieved axisymmetric circulation and suggests GBVTD-retrieved quantities can be useful in operational and research applications.

This study shows that turbulent kinetic energy (TKE) estimates, derived from static LiDARs in Doppler Beam Swing (DBS) mode, permit a qualitative and quantitative characterization and analysis of turbulent structures as wind turbine wakes, and convective or shear generated eddies in the lower atmospheric boundary layer. The analysed data, collected by a WINDCUBE™ v1 in a wind park in Austria, is compared to WINDCUBE™ v1 and sonic data from the WINd Turbine Wake EXperiment Wieringermeer (WINT-WEX-W). Although turbulence measurements with a WINDCUBE™ v1 are limited to a specific length scale, processed measurements above this threshold are in a good agreement with sonic anemometer data. In contrast to the commonly used turbulence intensity, the calculation of TKE not only provides an appropriate measure of turbulence intensities but also gives an insight into its origin. The processed data show typical wake characteristics, as flow decelerations, turbulence enhancement and wake rotation. By comparing these turbulence characteristics to other turbulent structures in the atmospheric boundary layer, we found that convection driven eddies in the surface layer have similar turbulence characteristics as turbine wakes, which makes convective weather situations relevant for wind turbine fatigue considerations.

Rolls observed during the Small Cumulus Microphysical Study (SCMS) field campaign are simulated using a large eddy model (LEM). The simulated boundary layer properties were in a good agreement with sounding profiles and aircraft observations, and the observed boundary layer rolls were reproduced by the model. Rolls started to decay when −Zi/L exceeded a threshold, with a value between 5 and 45. Here Zi and L refer to the height of the top of convective boundary layer and the Monin–Obukhov length, respectively. This value was found to depend on a nondimensional combination of the low-level wind shear, the height of the CBL, and the eddy velocity scale. Larger surface buoyancy fluxes and smaller shears gave higher thresholds. For the case modeled, rolls persisted for surface buoyancy fluxes less than 110 W m−2, and formed for boundary layer wind shears greater than 5 × 10−3 s−1, which is consistent with previous studies. The simulated roll convection was compared with a nonroll simula...

At noon on April 20, 2006, a wind storm occurred in Fujisawa City, Kanagawa Prefecture, Japan with a F0-P1-P1 rank on the Fujita-Pearson-scale (FPP-scale). Damage to over 40 residential buildings was observed. The damage covered an area 2 km by 50 m. The strong winds were accompanied by the passage of a cold front. Eyewitness accounts of a dust column and the recording of a pressure drop (1.5 hPa) indicate the existence of a tornado vortex. A hook-shaped radar echo (5 km in diameter) was observed in the narrow cold frontal rainband, with strong horizontal wind shear above the damage area. The Doppler velocity pattern indicated a misocyclone, which had a diameter of 2 km and a vorticity on the order of 10 2 s 1 . The wind storm may have caused the tornado, which formed in the cold frontal wind shear zone.

The possibility of velocity shear-induced linear transformations of different magnetohydrodynamic waves in the solar wind is studied both analytically and numerically. A quantitative analysis of the wave transformation processes for all possible plasma-β regimes is performed. By applying the obtained criteria for effective wave coupling to the solar wind parameters, we show that velocity shearinduced linear transformations of Alfvén waves into magneto-acoustic waves could effectively take place for the relatively low-frequency Alfvén waves in the energy containing interval. The obtained results are in a good qualitative agreement with the observed features of density perturbations in the solar wind.

A sheared background flow in a plasma induces coupling between different MHD wave modes, resulting in their mutual transformations with corresponding energy redistribution between the modes ). In this way, the energy can be transfered from one wave mode to the other, but energy can also be added to or extracted from the background flow. In the present paper it is investigated whether the wave coupling and energy transfer mechanisms can operate under solar wind conditions. It is shown that this is indeed the case. Hence, the long-period waves observed in the solar wind at r > 0.3 AU might be generated by much faster periodic oscillations in the photosphere of the Sun. Other possible consequences for the observable peculiar beat phenomena in the wind and acceleration of the wind particles are also discussed.

This study aimed to establish numerical models to replicate wind conditions for nearshore waters, sensitive to onshore topography, and to compare the characteristics of computational fluid dynamic (CFD) and mesoscale models. Vertical Doppler light detection and ranging (LiDAR) observation data were measured at an onshore site, which showed that wind conditions were affected by thermodynamic phenomena, such as land and sea breeze, and dynamical effects from neighboring onshore topography. The estimation accuracy of the CFD model depended on the height of the LiDAR data input. A height close to the target, such as the hub height of wind turbines, seemed appropriate as input data, considering that the accuracy of the wind speed shear replicated in a CFD numerical model may be uncertain. The mesoscale model replicated the wind through the thermodynamic effect and reliably estimated wind speed over nearshore waters without observation correction. Larger estimation errors were detected in...

This paper examines the three‐dimensional structure and dynamics of a south föhn flow in the Rhine Valley during its entire life cycle from 29 October 1999 until 31 October 1999. The south föhn event was documented in the framework of the Mesoscale Alpine Programme (MAP). This study investigates the synoptic‐scale forcing sources, the dynamical processes driving the circulation of the föhn flow in the complex network of tributaries of the Rhine Valley, and the degree of inhomogeneity on the scale of the FORM (‘FOehn in the Rhine Valley during the MAP’ programme) target area at the bifurcation between the Rhine and Seez Valleys. Several important data sources were used (ground‐based Doppler lidar, scintillometers, constant‐volume balloons, radiosoundings and surface stations) as well as non‐hydrostatic mesoscale simulations.The föhn penetrating the FORM target area on 30 October 1999 is preceded by a nocturnal shallow föhn phase which does not penetrate down to the ground due to kata...

A simplified model of the Atmospheric Boundary Layer (ABL) of intermediate complexity between a bulk parameterization and a three-dimensional atmospheric model is developed and integrated to the Nucleus for European Modelling of the Ocean (NEMO) general circulation model. An objective in the derivation of such simplified model called ABL1d is to reach an apt representation in ocean-only numerical simulations of some of the key processes associated to air/sea interactions at the characteristic scales of the oceanic mesoscale. In this paper we describe the formulation of the ABL1d model and the strategy to constrain this model with large-scale atmospheric data available from reanalysis or real-time forecasts. A particular emphasis is on the appropriate choice and calibration of a turbulent closure scheme for the atmospheric boundary layer. This is a key ingredient to properly represent the air/sea interaction processes of interest. We also provide a detailed description of the NEMO-ABL1d coupling infrastructure and its computational efficiency. The resulting simplified model is then tested for several boundary-layer regimes relevant to either ocean/atmosphere or sea-ice/atmosphere coupling. The coupled system is also tested with a realistic 0.25 • resolution global configuration. The numerical results are evaluated using standard metrics from the literature to quantify the wind/sea surface temperature (a.k.a. thermal feedback effect), wind/currents (a.k.a. current feedback effect) and ABL/sea-ice couplings. With respect to these metrics, our results show very good agreement with observations and fully coupled ocean-atmosphere models for a computational overhead of about 9% in term of elapsed time compared to standard uncoupled simulations. This moderate overhead, largely due to I/O operations, leaves room for further improvement to relax the assumption of horizontal homogeneity behind ABL1d and thus to further improve the realism of the coupling while keeping the flexibility of ocean-only modelling. Owing to advances in computational power, global oceanic models used for research or operational purposes are now configured with increasingly higher horizontal/vertical resolution thus resolving the baroclinic deformation radius in the tropics (e.g.

Greece was hit by an extreme heat wave, with a significant impact on human health and natural ecosystems in the period between 28 July and 11 August 2021. After the end of this unusual warm period, a rare occasion of multiple supercell storms was observed on 11 August 2021 in northern and central Greece. The synoptic conditions indicated embedded short waves in a northwesterly flow and significant thermal instability across the regions of interest was evident. In conjunction with the strong vertical wind, shear organized convection was released. At least six long-track supercells were documented and the onset, evolution and specific characteristics of them are presented. All supercells moved from NW toward SE, accompanied by large hail, intense rainfall and destructive wind gusts, producing widespread damage along their track.

This paper examines the impact of a mesoscale analysis (2.5 km grid distance) on the simulation of the meso-gamma scale aspects of föhn in the Rhine Valley. The föhn event, documented during IOP 15 (5 November 1999) of the Mesoscale Alpine Programme, was standard in terms of intensity and was characterized by an important temporal variability. Many instruments operating in the Rhine Valley target area are used to validate the simulation, in particular the airborne nadir pointing lidar LEANDRE 2 (flown over the Lower Rhine Valley) as well as a windprofiler and a radio accoustic sounding system colocated in Rankweil, Austria. The large observational dataset acquired during the IOP allowed documentation of the entire föhn life cycle. For most of the IOP, a cold pool remained near the ground in the lower northern part of the valley. The non-hydrostatic model meso-NH, used in a grid-nesting configuration with two nested models and initialised with a mesoscale analyse, allowed to simulate realistically the location and depth of the cold pool. The relationship between the föhn intensity and the large scale environment is also examined. The flow regime is a flow around the Alps. The variability of this flow at the western tip of the Alps could explain some of the temporal changes observed at low level in the Rhine valley.

On 4 May 2007, a supercell produced an EF-5 tornado that severely damaged the town of Greensburg, Kansas. Volumetric data were collected in the “Greensburg storm” by the University of Massachusetts X-band, mobile, polarimetric Doppler radar (UMass X-Pol) for 70 min; 10 tornadoes were detected. This mobile Doppler radar dataset is one of only a few documenting an EF-5 tornado and the supercell’s transition from short-track, cyclic tornado production (mode 1) to long-track tornado production (mode 2). Using bootstrap confidence intervals, it is determined that the mode-2 tornadoes moved in the same direction as the supercell vault. In contrast, the mode-1 tornadoes moved to the left with respect to the vault.From polarimetric data collected in this storm, the authors infer the presence of large, oblate drops (high ZDR, high ρhv) in the forward flank and surrounding some of the tornadoes. The authors speculate that the weak-echo column (WEC) in the Greensburg tornado, which extended ab...

The Nice Côte d'Azur international airport is subject to horizontal low-level wind shears. Detecting and predicting these hazards is a major concern for aircraft security. A measurement campaign took place over the Nice airport in 2009 including 4 anemometers, 1 wind lidar and 1 wind profiler. Two wind shear events were observed during this measurement campaign. Numerical simulations were carried out with Meso-NH in a configuration compatible with near-real time applications to determine the ability of the numerical model to predict these events and to study the meteorological situations generating an horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

Doppler SODAR (Sound Detection and Ranging) measurements over a tropical Indian station at National Atmospheric Research Laboratory (NARL), Gadanki (13.5 • N, 79.2 • E) during two consecutive monsoon seasons, 2007 and 2008, are investigated to study the influence of mechanically generated turbulence on temperature structure parameter (C 2 T ) in the convective boundary layer. Increase in the C 2 T is observed after the arrival of monsoon for both seasons. Contribution of vertical wind shear in horizontal wind component to C 2 T due to zonal winds is responsible for the increase observed in the temperature structure parameter which is inferred from the results obtained. C 2 T is found to be increased by an order of 2 in both the lower and upper altitudes, respectively. Magnitude of wind speed is reported to be doubled with the arrival of monsoon. It is also observed that, southwest monsoon wind modulates the day-to-day variations of wind pattern over this station during the onset phase of monsoon season. The lower variability observed at lower height is attributed to the complex topography surrounding this region.

This study identifies high-impact severe weather events with poor predictive skill over the northeast United States using Storm Prediction Center (SPC) convective outlooks. The objectives are to build a climatology of high-impact, low predictive skill events between 1980 and 2013 and investigate the differences in the synopticscale environment and severe weather parameters between severe weather events with low predictive skill and high predictive skill. Event-centered composite analyses, performed using the National Centers for Environmental Prediction Climate Forecast System Reanalysis and the North American Regional Reanalysis, suggest low predictive skill events occur significantly more often in low-shear environments. Additionally, a plurality of low probability of detection (POD), high-impact events occurred in low-shear, high-CAPE environments. Statistical analysis of low-shear, high-CAPE environments suggests high downdraft CAPE (DCAPE) and relatively dry lower levels of the atmosphere are associated with widespread severe weather events. DCAPE and dry boundary layer air may contribute to severe wind gusts through strong negative buoyancy and enhanced evaporative cooling of descending saturated parcels.

Most current general circulation models (GCMs) calculate radiative fluxes through partially cloudy grid boxes by weighting clear and cloudy fluxes by the fractional area of cloud cover (Ca), but most GCM cloud schemes calculate cloud fraction as the volume of the grid box that is filled with cloud (Cυ). In this paper, 1 yr of cloud radar and lidar observations from Chilbolton in southern England, are used to examine this discrepancy. With a vertical resolution of 300 m it is found that, on average, Ca is 20% greater than Cυ, and with a vertical resolution of 1 km, Ca is greater than Cυ by a factor of 2. The difference is around a factor of 2 larger for liquid water clouds than for ice clouds, and also increases with wind shear. Using Ca rather than Cυ, calculated on an operational model grid, increases the mean total cloud cover from 53% to 63%, and so is of similar importance to the cloud overlap assumption. A simple parameterization, Ca = [1 + e(−f )(C−1υ − 1)]−1, is proposed to c...

Pakistan experiences several torrential rainfall events for many years due to interactive role of midlatitude atmospheric and warm moist monsoon circulations. Deadly events such as flash flooding, runoff, and mudslides may trigger by torrential rainfall events which pose significant threat to human assets. This study was undertaken based on three severe weather events (1988, 2010, and 2013) by using percentage departure to identify wet and dry years during the period 1985–2016, which occurred over northern Pakistan. Rainfall data were obtained from 14 synoptic stations of Pakistan Meteorological Department, which were analyzed at daily, monthly, and annual bases. The data sets of Climate Research Unit, Global Precipitation Climatology Centre, and Pakistan Meteorological Department are used to justify the Weather Research and Forecasting model simulation and for analyzing the various atmospheric and diagnostic variables. Results showed teleconnection between large‐scale circulation p...

In the present study, we analyzed the wind measurements in the troposphere and lower stratosphere over Andøya in northern Norway (69.30°N, 16.04°E) with the Middle Atmosphere Alomar Radar System (MAARSY) from 2017 to 2020. We calculated the momentum flux and vertical wind power spectra using the fast Fourier transformation (FFT) analysis technique. The spectra are characterized into different regions based on: frequency (lower and higher than (13 h) -1 , since the local inertial period over Andøya is 13 h), altitudes (lower troposphere, middle troposphere, tropopause region, and lower stratosphere), and seasons (spring, summer, autumn, and winter). We report for the first time that both the momentum flux spectra and vertical wind power spectra display a seasonal and altitudinal variation with the minimum in summer and the maximum magnitude in the troposphere. We also studied the intermittency of the waves during this period using the Gini coefficient over Northern Norway for the first time, which is used to distinguish the intermittent wave periodicities from the non-intermittent ones. We reveal that the high-frequency (short-period oscillations) gravity waves are more intermittent than the low-frequency (longperiod oscillations). Additionally, the most intermittent waves are located in the lower stratospheric altitudes for low-frequency waves, while the high-frequency waves are dominantly intermittent in the whole altitude region with small patches of lower intermittency region.

The influence of slope, height, and Weibull wind characteristics of terrain highly affect the wind power capacity of the wind farm. Before the installation of a wind farm, it is very beneficial to know about the complexity of our using site. This complexity of terrain is decided by RIX (Ruggedness Index) value. The economic profit in wind farm investment is purely dependent on energy production is forecasted before the installation of the wind turbine. This paper is about the complexity of terrain and wind resources assessment at Mamatkheda Ratlam [M.P.]. The digital elevation model of terrain on the selected site is obtained using ArcGIS software and then later on digitized roughness model in WAsP software. The wind data is further extrapolated at height heights while considering the effect of different roughness length. The result indicates the ruggedness index factor for the terrain is 0.2 which satisfies the condition of flat terrain.

The importance of characterizing the wind shear at a specified location for the utilization of wind turbine is of vital importance. Such study is considered necessary both for the turbine design and prediction of its power output. In situations where the wind speed at different heights is required if measured values are known at one height then, generally it is extrapolated to the hub height by using the one-seventh power law. The exponent in this case has a value of 1/7 but it is observed that, the value of exponent varies with the type of terrain therefore; the one-seventh power law is not suitable for wind speed extrapolation and energy estimation. It has been found that, the one-seventh power law has a tendency to miscalculate the actual long-term average wind speeds. Hence, for accurate estimation of wind speed at a height, both monthly or seasonal and diurnal values of wind shear coefficient (WSC) have to be used. In this paper, the power law exponent for three sites located o...

A 38‐day long time series obtained using a combination of moored Wirewalkers equipped with conductivity‐temperature‐depth profilers and bottom‐mounted and subsurface acoustic Doppler current profilers provided detailed high‐resolution observations that resolved near‐surface velocity and vertical and cross‐shelf density gradients of the Chesapeake Bay plume far field. This unprecedented data set allowed for a detailed investigation of the impact of wind forcing on the thermal wind shear of a river plume. Our results showed that thermal wind balance was a valid approximation for the cross‐shelf momentum balance over the entire water column during weak winds ( 0.075 Pa), and it was also valid within the interior during moderate downwelling (−0.125 0.075 Pa). Stronger wind conditions, however, resulted in the breakdown of the thermal wind balance in the Chesapeake Bay plume, with thermal wind shear overestimating the observed shear during downwelling and underestimating during upwelling...

The annual mean number of tropical cyclones in the Central North Pacific (CNP) is approximately three. Although this number is low in comparison to other basins, the interannual variability of tropical cyclones, which includes tropical storms and hurricanes, is high. For the period 1966-1997, the annual number ranges from 0 to 10 tropical cyclones. There is a large and positive correlation between CNP tropical cyclone counts and El Nin ˜o 3.4 region SST anomalies with a 95% significance level. In the El Nin ˜o Hurricane Season (ENHS), a greater number of cyclones formed in the CNP and more cyclones propagated into this area from the east. The monsoon trough, low level relative vorticity, and tropospheric vertical wind shear in the CNP undergo pronounced changes during warm and cold phases of ENSO. For instance, the 1000 hPa relative vorticity values within the CNP in an El Nin ˜o autumn composite are double the values in a corresponding La Nin ˜a composite. The El Nin ˜o autumn composite of tropospheric vertical wind shear shows a two to three times reduction equatorward of 16 N-17 N when compared to the La Nin ˜a autumn composite. The increased values of the dynamic potential term in Gray's (1977) seasonal genesis parameter correspond well with the increased cyclone frequency in the CNP for an ENHS composite. Furthermore, a majority of initial detection points of named storms is found within a band of relatively large values of dynamic potential. This suggests that this term can be used to diagnose favorable areas for tropical cyclogenesis on a seasonal time scale.

This paper investigates the influence of 3p oscillations caused by wind shear and tower shadow on the power output of wind turbines and small signal stability of power systems incorporating wind turbines. First, the time-domain inputs of factors that affect 3p oscillations are modelled and its effect on power system small signal stability are determined via modal analysis. The whole system is modelled using power system toolbox in Matlab environment. Some of the key results reveal that 3p oscillations could result into fluctuating electric power fed to the grid, however, it may not necessarily result into small signal instability of the grid.

We propose a data-driven model to predict the short-term fatigue Damage Equivalent Loads (DEL) on a wake-affected wind turbine based on wind field inflow sensors and/or loads sensors deployed on an adjacent up-wind wind turbine. Gaussian Process Regression (GPR) with Bayesian hyperparameters calibration is proposed to obtain a surrogate from input random variables to output DELs in the blades and towers of the up-wind and wake-affected wind turbines. A sensitivity analysis based on the hyperparameters of the GPR and Kullback-Leibler divergence is conducted to assess the effect of different input on the obtained DELs. We provide qualitative recommendations for a minimal set of necessary and sufficient input random variables to minimize the error in the DEL predictions on the wake-affected wind turbine. Extensive simulations are performed comprising different random variables, including wind speed, turbulence intensity, shear exponent and inflow horizontal skewness. Furthermore, we include random variables related to the blades lift and drag coefficients with direct impact on the rotor aerodynamic induction, which governs the evolution and transport of the meandering wake. In addition, different spacing between the wind turbines and W€ ohler exponents for calculation of DELs are considered. The maximum prediction normalized mean squared error, obtained in the tower base DELs in the fore-aft direction of the wake affected wind turbine, is less than 4%. In the case of the blade root DELs, the overall prediction error is less than 1%. The proposed scheme promotes utilization of sparse structural monitoring (loads) measurements for improving diagnostics on wake-affected turbines.

Possible changes in the Asian summer monsoon due to increased atmospheric CO2 are investigated by an MRI global coupled atmosphere-ocean general circulation model. The summer (June-August) monsoon rainfall in India increases significantly with global warming. On the other hand, the monsoon wind shear index, defined as the difference between 850 hPa and 200 hPa zonal winds over the northern Indian Ocean, decreases. At 850 hPa, the westerly wind shifts northward and intensifies from the Sahel to northwest of India, but the monsoon westerly over the Arabian Sea weakens. It is found that increased moisture content in the warmer air leads to larger moisture flux convergence, contributing to the increased rainfall. Therefore, the monsoon wind shear index is not a good indicator for identifying any change of monsoon accompanying global warming. In contrast to the increased rainfall in India, change in rainfall is little over China where soil moisture becomes drier at times of increased CO2. It is also noted that the northern Eurasian continent becomes wetter in the increased-CO2 climate. The magnitude of the interannual variability of the Asian summer monsoon rainfall becomes larger in the CO2 experiment than in the control experiment, particularly in the later stage of the experiment after CO2 doubling. However it should be noted that the interdecadal variation of this interannual variability is also large both in the control and the CO2 experiments.

This work aims to study the seasonal difference in normalized wind speed above the surface layer as it is observed at the 160 m high mast at the coastal site Høvsøre at winds from the sea (westerly). Normalized wind speeds above the surface layer are observed to be 20 to 50 % larger in the winter/spring seasons compared to the summer/autumn seasons at winds from west within the same atmospheric stability class. A method combining the mesoscale model, COAMPS, and observations of the surface stability of the marine boundary layer is presented. The objective of the method is to reconstruct the seasonal signal in wind speed and identify the physical process behind. The method proved reasonably successful in capturing the relative difference in wind speed between seasons, indicating that the simulated physical processes are likely candidates to the observed seasonal signal in normalized wind speed.

We evaluate forecasts made with the WRF ARW model run with seven different boundary layer (BL) parameterizations. The simulations are evaluated in terms of the best performance in wind energy forecasting, i.e. in forecasting winds at hub height as well as the correct shape of the wind shear. The model runs are short-term wind forecasts (0-30 hours) for October 2009 and are compared to measurements from the 116/160meter meteorological mast/light tower at the Risø National Test Station for Large Wind Turbines at Høvsøre, Denmark. When evaluating wind profiles, we compute the α-parameter, a measure for stability derived from the power law. The results show that the YSU BL scheme does not exhibit the desired variation in the wind profiles from stable to unstable in the course of a day and tends to nearly always produce vertical wind shear typical of the neutral atmosphere. The wind profiles forecast with WRF using the BL schemes based on turbulence kinetic energy, however, compare better with the observations. All the evaluated schemes tend to underestimate the wind at hub height during the night and overestimate it during the day. The diurnal evolution and the expected transitions of wind speed, temperature and the α-parameter are well captured by all of the schemes, except for the YSU scheme.

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Wind measurements are generally performed below wind turbine hub heights due to higher measurement and tower costs. In order to obtain the wind speed at the hub height of the turbine, the measurements are extrapolated, assuming that the wind shear is constant. This assumption may result in some critical errors between the estimated and actual energy outputs. In this paper wind data collected in Balıkesir from October 2008 to September 2009, has been used to show the effects of wind shear coefficient on energy production. Results of the study showed that, the difference between wind energy production using extrapolated wind data and energy production using measured wind data at hub height may be up to 49.6%.

Wind shear coefficient (WSC) analysis and energy yield estimation were performed at a coastal and an inland location in Namibia using 10-minute average wind speeds collected at the two locations over a period of one year (January to December 2013). To enable proper understanding of wind shear trends, WSCs, and roughness lengths, wind data were observed at two heights (i.e., 20.88 m and 48.14 m above ground level (AGL) at Terrace Bay (TB) and (23.49 m and 50.49 m AGL) at Okanapehuri (OP). The computations resulted in overall mean values of WSCs of 0.0463 and 0.24 at TB and OP, respectively, and roughness lengths (z0) of 0.000000673 m and 0.526 m at TB and OP, respectively. The variations of WSCs and z0 by months, hours and direction were thoroughly analysed and described. At the coast, sea/land interface significantly influenced WSCs and z0, resulting in lower than expected mean values, whereas at OP, the transitional nature of the vegetation shaped the pattern observed. Based on the...

Zonal available potential energy (Az) is an estimate of the amount of potential energy in the atmosphere available for conversion to kinetic energy, providing a good proxy for the overall strength of the general circulation. Previous studies have estimated total hemispheric Az, Az generation, and conversion to kinetic energy, and proposed physical mechanisms to describe the annual Az cycle as well as short term (sub-seasonal to synoptic) APE depletion events. Large, short term modulations of Az have been shown to be associated with impactful weather events in the mid-and high-latitudes, including severe cyclones and high-amplitude ridging and blocking events In this study, we examine the association of significant synoptic time-scale winter season increases in Az with dynamic tropopause wave break events. Az buildup events are determined using a 1979-2011 daily Northern Hemisphere (20°-85° N) Az climatology calculated from the National Centers for Environmental Prediction (NCEP) Department of Energy (DOE) Reanalysis 2 global reanalysis dataset in an isobaric framework. To diagnose the importance of wave breaks in the troposphere, we objectively identify wave breaks using potential temperature on the dynamic tropopause, identifying and tracking both anti-cyclonic (LC1) and cyclonic (LC2) wave breaks during the 1979-2011 period. Our results indicate that LC1 wave break events in the equatorward North Pacific jet exit regions appear to play an important role in Az buildup events. We further assess the large-scale environmental factors leading to the onset of anomalously high LC1 wave breaking in the Pacific basin, as well as examining the role of these wave break events in not only warming the subtropical air mass but also modifying the arctic environment resulting in rapid lower-tropospheric cooling events.

The nocturnal low-level jet (LLJ) and orographic (gravity) waves play an important role in the generation of turbulence and pollutant dispersion and can affect the energy production by wind turbines. Additionally, gravity waves have an influence on the local mixing and turbulence within the surface layer and the vertical flux of mass into the lower atmosphere. On 25 September 2017 during a field campaign, a persistent easterly LLJ and gravity waves are observed simultaneously in a coastal area in the north of France. In the present study, an attempt is to explore the variability of the wind speed, turbulent eddies, and turbulence kinetic energy in the time-frequency and space domain using an ultrasonic anemometer and a scanning wind lidar. The results reveal a significant enhancement of the turbulence kinetic energy dissipation (by ~50%) due to gravity waves in the LLJ shear layer (below the jet core) during the period of wave propagation. Large values of zonal and vertical components of the shear stress (~|0.4| and ~|1.5| m 2 s -2 respectively) are found during that period. Large size eddies (~110 to 280 m), matching high-speed wind regime, are found to propagate the momentum downward. This enhances the downward mass transport from the LLJ shear layer to the roughness layer. Furthermore, these large-scale eddies are associated with the crests while comparatively small-scale eddies are associated with the troughs of the gravity wave.

This paper investigates the influence of 3p oscillations caused by wind shear and tower shadow on the power output of wind turbines and small signal stability of power systems incorporating wind turbines. First, the time-domain inputs of factors that affect 3p oscillations are modelled and its effect on power system small signal stability are determined via modal analysis. The whole system is modelled using power system toolbox in Matlab environment. Some of the key results reveal that 3p oscillations could result into fluctuating electric power fed to the grid, however, it may not necessarily result into small signal instability of the grid.

The daytime atmospheric convective boundary layer (CBL) is characterized by strong turbulence that is primarily caused by buoyancy forced from the heated underlying surface. The present study considers a combination of a virtual radar and large eddy simulation (LES) techniques to characterize the CBL. Data representative of a daytime CBL with wind shear were generated by LES and used in the virtual boundary layer radar (BLR) with both vertical and multiple off-vertical beams and frequencies. To evaluate the virtual radar, a multiple radar experiment (MRE) was conducted using five virtual radars with common resolution volumes at two different altitudes. Three-dimensional wind fields were retrieved from the virtual radar data and compared with the LES output. It is shown that data produced from the virtual BLR are representative of what one expects to retrieve using a real BLR and the measured wind fields match those of the LES. Additionally, results from a frequency domain interferom...

Using the AIRS retrieved temperature and humidity profiles, the Saharan Air Layer (SAL) influence on the formation of Hurricane Isabel (2003) is simulated numerically with the MM5 model. The warmth and dryness of the SAL (the thermodynamic effect) is assimilated by use of the nudging technique, which enables the model thermodynamic state to be relaxed to the profiles of the AIRS retrieved data for the regions without cloud contamination. By incorporating the AIRS data, MM5 better simulates the large‐scale flow patterns and the timing and location of the formation of Hurricane Isabel and its subsequent track. By comparing with an experiment without nudging of the AIRS data, it is shown that the SAL may have delayed the formation of Hurricane Isabel and inhibited the development of another tropical disturbance to the east. This case study confirms the argument by Dunion and Velden (2004) that the SAL can suppress Atlantic tropical cyclone activity by increasing the vertical wind shear...

As the global wind energy industry advances to larger wind turbine systems, there still remains opportunities for deploying single medium-to-large-scale wind turbines in distributed wind energy applications. These include community wind farms and "behind-the-meter" wind applications. Such sites tend to be closer to population centres at lower elevations that have more complex wind regimes due to surrounding orography, local terrain and obstacles such as buildings. This research case study examines the regional mesoscale influences and local microscale influences on the post construction measured energy performance of an 850 kW rated wind turbine, with a 60 m hub height, at a peri-urban coastal location. The remodelled Irish wind atlas is used to characterise mesoscale and microscale influences on wind resource around the wind turbine site. A directional analysis of modelled predicted annual energy is compared to the measured wind turbine electrical energy rose. Data from a nine month LiDAR measurement campaign is used to assess directional wind shear profiles at the site. The shear profiles are examined with respect to local buildings obstacles to gain insights into the microscale sources of discrepancies between the predicted energy from the wind atlas and actual energy output of the wind turbine.

As the global wind energy industry advances to larger wind turbine systems, there still remains opportunities for deploying single medium-to-large-scale wind turbines in distributed wind energy applications. These include community wind farms and "behind-the-meter" wind applications. Such sites tend to be closer to population centres at lower elevations that have more complex wind regimes due to surrounding orography, local terrain and obstacles such as buildings. This research case study examines the regional mesoscale influences and local microscale influences on the post construction measured energy performance of an 850 kW rated wind turbine, with a 60 m hub height, at a peri-urban coastal location. The remodelled Irish wind atlas is used to characterise mesoscale and microscale influences on wind resource around the wind turbine site. A directional analysis of modelled predicted annual energy is compared to the measured wind turbine electrical energy rose. Data from a nine month LiDAR measurement campaign is used to assess directional wind shear profiles at the site. The shear profiles are examined with respect to local buildings obstacles to gain insights into the microscale sources of discrepancies between the predicted energy from the wind atlas and actual energy output of the wind turbine.