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Wind shear

About: Wind shear is a research topic. Over the lifetime, 8023 publications have been published within this topic receiving 185373 citations.


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Journal ArticleDOI
TL;DR: In this article, a portable data recorder attached to the Weather Surveillance Radar-1957 (WSR-57) in Apalachicola, Florida, collected 313 radar scans of the reflectivity structure within 150 km of the center of Hurricane Elena (in 1985) between 1310 and 2130 UTC 1 September.
Abstract: A portable data recorder attached to the Weather Surveillance Radar-1957 (WSR-57) in Apalachicola, Florida, collected 313 radar scans of the reflectivity structure within 150 km of the center of Hurricane Elena (in 1985) between 1310 and 2130 UTC 1 September. This high temporal and spatial (750 m) resolution dataset was used to examine the evolution of the symmetric and asymmetric precipitation structure in Elena as the storm rapidly strengthened and attained maximum intensity. Fourier decomposition of the reflectivity data into azimuthal wavenumbers revealed that the power in the symmetric (wavenumber 0) component dominated the reflectivity pattern at all times and all radii by at least a factor of 2. The wavenumber 1 asymmetry accounted for less than 20% of the power in the reflectivity field on average and was found to be forced by the environmental vertical wind shear. The small-amplitude wavenumber 2 asymmetry in the core was associated with the appearance and rotation of an elliptical eyewall. This structure was visible for nearly 2 h and was noted to rotate cyclonically at a speed equal to half of the local tangential wind. Outside of the eyewall, individual peaks in the power in wavenumber 2 were associated with repeated instances of cyclonically rotating, outward-propagating inner spiral rainbands. Four separate convective bands were identified with an average azimuthal velocity of 25 m s 1 ,o r68% of the local tangential wind speed, and an outward radial velocity of 5. 2ms 1 . The azimuthal propagation speeds of the elliptical eyewall and inner spiral rainbands were consistent with vortex Rossby wave theory. The elliptical eyewall and inner spiral rainbands were seen only in the 6-h period prior to peak intensity, when rapid spinup of the vortex had produced an annular vorticity profile, similar to those that have been shown to support barotropic instability. The appearance of an elliptical eyewall was consistent with the breakdown of eyewall vorticity into mesovortices, asymmetric mixing between the eye and eyewall, and a slowing of the intensification rate. The inner spiral rainbands might have arisen from high eyewall vorticity ejected from the core during the mixing process. Alternatively, because the bands were noted to emanate from the vertical shear-forced deep convection in the northern eyewall, they could have formed through the axisymmetrization of the asymmetric diabatically generated eyewall vorticity.

103 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of wind shear, wind speed, turbulence intensity, rotor position and tower oscillation on the power pulsation of a three-bladed wind turbine is investigated.
Abstract: In this paper, periodic power pulsations from a three-bladed wind turbine are analyzed. The influence of wind shear, wind speed, turbulence intensity, rotor position and tower oscillation is investigated. No clear dependence between the periodic power components and the wind shear or turbulence intensity has been verified. The investigated turbine sometimes produces large power pulsations at the tower resonance frequency. These occur when the turbine oscillates in the sideways direction of the nacelle.

103 citations

Proceedings ArticleDOI
Naoto Ebuchi1
09 Jul 2001
TL;DR: In this article, the QuikSCAT/SeaWind Data Products (Level 2B) were collocated with the Japan Meteorological Agency (JMA), National Data Buoy Center (NDBC), and Tropical Atmosphere Ocean (TAO) buoys.
Abstract: Wind vectors observed by QuikSCAT/SeaWinds are compared with wind and wave data from offshore moored buoys. Effects of oceanographic and atmospheric parameters on the scatterometry are also assessed by using the buoy data. The QuikSCAT/SeaWinds Standard Wind Data Products (Level 2B) were collocated with the Japan Meteorological Agency (JMA), National Data Buoy Center (NDBC), and Tropical Atmosphere Ocean (TAO) buoys. Only buoys located offshore and in deep water were selected. Temporal difference and spatial separation between the QuikSCAT/SeaWinds and buoy observations were limited to less than 30 min and 25 km. Wind speeds measured by the buoys at various height above the sea surface were corrected to equivalent neutral winds at a height of 10 m. Wind speeds and directions observed by QuikSCAT/SeaWinds agree well with the buoy data. Root-mean- squared differences of the wind speed and direction are 1.02 m/s and 22/spl deg/, respectively. Dependencies of wind speed residuals on oceanographic and atmospheric parameters observed by buoys are examined using the collocated data. Weak positive correlation of the wind speed residuals with the significant wave height is found, although no significant dependence on the sea surface temperature and atmospheric stability is discernible.

103 citations

Journal ArticleDOI
TL;DR: In this article, the authors simulate inhomogeneous flow in the atmospheric boundary layer, notably stably stratified flow past a wind turbine, with a mean wind speed of 6.5 m s−1 at the turbine hub-height of 80 m.
Abstract: . Wind-profiling lidars are now regularly used in boundary-layer meteorology and in applications such as wind energy and air quality. Lidar wind profilers exploit the Doppler shift of laser light backscattered from particulates carried by the wind to measure a line-of-sight (LOS) velocity. The Doppler beam swinging (DBS) technique, used by many commercial systems, considers measurements of this LOS velocity in multiple radial directions in order to estimate horizontal and vertical winds. The method relies on the assumption of homogeneous flow across the region sampled by the beams. Using such a system in inhomogeneous flow, such as wind turbine wakes or complex terrain, will result in errors. To quantify the errors expected from such violation of the assumption of horizontal homogeneity, we simulate inhomogeneous flow in the atmospheric boundary layer, notably stably stratified flow past a wind turbine, with a mean wind speed of 6.5 m s−1 at the turbine hub-height of 80 m. This slightly stable case results in 15° of wind direction change across the turbine rotor disk. The resulting flow field is sampled in the same fashion that a lidar samples the atmosphere with the DBS approach, including the lidar range weighting function, enabling quantification of the error in the DBS observations. The observations from the instruments located upwind have small errors, which are ameliorated with time averaging. However, the downwind observations, particularly within the first two rotor diameters downwind from the wind turbine, suffer from errors due to the heterogeneity of the wind turbine wake. Errors in the stream-wise component of the flow approach 30% of the hub-height inflow wind speed close to the rotor disk. Errors in the cross-stream and vertical velocity components are also significant: cross-stream component errors are on the order of 15% of the hub-height inflow wind speed (1.0 m s−1) and errors in the vertical velocity measurement exceed the actual vertical velocity. By three rotor diameters downwind, DBS-based assessments of wake wind speed deficits based on the stream-wise velocity can be relied on even within the near wake within 1.0 m s−1 (or 15% of the hub-height inflow wind speed), and the cross-stream velocity error is reduced to 8% while vertical velocity estimates are compromised. Measurements of inhomogeneous flow such as wind turbine wakes are susceptible to these errors, and interpretations of field observations should account for this uncertainty.

102 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present the results from the 1995 season of site-testing experiments at the South Pole, in which the seeing was measured using balloon-borne microthermal probes.
Abstract: Results from the 1995 season of site-testing experiments at the South Pole are presented, in which the seeing was measured using balloon-borne microthermal probes. Our analysis shows a marked division of the atmosphere into two characteristic regions: (i) a highly turbulent boundary layer (0-220 m) associated with a strong temperature inversion and wind shear, and (ii) a very stable free atmosphere. The mean seeing, averaged over 15 balloon flights, was measured to be 1.86″, of which the free atmosphere component was only 0.37″. The seeing from ~200 m upward is superior to the leading mid-latitude sites (e.g. Fuchs 1995; Roddier et al. 1990) by almost a factor of two. The results are in good agreement with optical seeing data obtained by a differential image motion monitor on three of the five occasions when the two measurements were performed simultaneously. The boundary layer winds are of katabatic origin, and so we may consider the possibility of exceptional seeing conditions from surface level at other locations on the plateau such as Domes A and C, where there is little or no katabatic wind. In addition, the proximity of the optical turbulence to the focus of a telescope situated at ground level is a highly favourable situation for the use of adaptive optics, since the wavefront spatial coherence scale is related to the altitude of the turbulent layers producing the image distortion. Some comparisons are made between the relevant adaptive optics parameters measured at the South Pole and Cerro Paranal, one of the best mid-latitude sites.

102 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023155
2022347
2021165
2020157
2019187
2018165