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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, the authors review the current knowledge of the turbulent structure of the upper part of the atmospheric boundary layer capped by a cloud deck, in the light of recent observations and model studies.
Abstract: Extended sheets of stratocumulus (Sc) in the upper part of the atmospheric boundary layer (ABL) often occur under appropriate meteorological conditions. These cloud decks are important both in climate studies and in weather forecasting. We review the current knowledge of the turbulent structure of the ABL capped by a cloud deck, in the light of recent observations and model studies. The most important physical processes determining this structure are longwave radiative cooling at cloud top, shortwave radiative wanning by absorption in the cloud, surface buoyancy flux, and wind shear in the ABL. As a result, turbulence can cause entrainment against the buoyancy jump at cloud top. In cases where only longwave radiative fluxes and surface buoyancy fluxes are important, the turbulent structure is relatively well understood. When shortwave radiative fluxes and/or wind shear are also important, the resulting turbulent structure may change considerably. A decoupling of the cloud from the sub-cloud layer or of the top of the cloud from the rest of the ABL is then regularly observed. In no cases are the details of the entrainment at cloud top understood well enough to derive a relatively simple formulation that is consistent with observations. Cloud-top entrainment instability may lead to the break-up of a cloud deck (but also to cloud deepening). The role of mesoscale circulations in determining fractional cloudiness is not yet well understood.

72 citations

Book ChapterDOI
TL;DR: The contribution of buoyancy fluxes to turbulence at the air-water interface has not received the same attention as the contribution of wind and surface waves in estimating the gas transfer coefficient as mentioned in this paper.
Abstract: Physical processes at the air-water interface that affect gas flux include turbulence from wind shear, penetrative convection due to heat loss, micro-wave breaking, and large scale wave breaking. While considerable effort has been expended to parameterize the gas transfer coefficient due to the contributions of wind and surface waves, the contribution of buoyancy fluxes to turbulence at the air-water interface has not received the same attention. In addition, the rate of mixed layer deepening is sensitive to heat loss. Without this deepening, gas concentrations quickly equilibrate with those in the atmosphere leading to lower rates of gas flux. Measured gas flux was up to 5 times higher when heat was being lost from the surface layer of an arctic lake and wind speeds were low than when wind speeds were 5 m s -1 . At wind speeds less than 5 m s -1 , calculated values of gas transfer velocity based on wind speed alone were 2 to 5 times lower than those calculated using the surface renewal model. These observations indicate the critical importance of including buoyancy fluxes in estimates of gas transfer coefficients.

72 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of free-stream wind shear on the wake structure and performance characteristics of a horizontal axis wind turbine rotor was investigated using a new three-dimensional unsteady vortex-panel method potential flow solver based on a free-vortex wake methodology.
Abstract: This paper presents an investigation of the effect of steady and transient free-stream wind shear on the wake structure and performance characteristics of a horizontal axis wind turbine rotor. A new three-dimensional unsteady vortex-panel method potential flow solver based on a free-vortex wake methodology, AeroSIM+, is used for this purpose. The code is validated using the experimental data from the National Renewable Energy Laboratory Unsteady Aerodynamics Experiments. The effects of vortex core model, core size, expansion, and filament stretching on torque and thrust predictions are investigated. Three-different wind shear cases, i.e., uniform inflow (no wind shear), steady vertical wind shear that uses a power law velocity profile (Normal Wind Profile, NWP) and transient Extreme Wind Shear (EWS), are investigated. The results show that the existence of wind shear can create a very complex wake structure with substantial asymmetries, streamwise vorticity generation, and non-periodicities downstream of the turbine rotor. In addition, the blades are subjected to asymmetrical surface pressure variations that in turn result in high amplitude fluctuations in power and thrust levels generated by the turbine. Copyright © 2011 John Wiley & Sons, Ltd.

72 citations

Journal ArticleDOI
TL;DR: In this paper, a version of the Kaplan and DeMaria empirical model for predicting the decay of tropical cyclone 1-min maximum sustained surface winds after landfall is developed for the New England region.
Abstract: A version of the Kaplan and DeMaria empirical model for predicting the decay of tropical cyclone 1-min maximum sustained surface winds after landfall is developed for the New England region. The original model was developed from the National Hurricane Center (NHC) best-track wind estimates for storms that made landfall in the United States south of 37°N from 1967 to 1993. In this note, a similar model is developed for U.S. storms north of 37°N, which primarily made landfall in New York or Rhode Island and then moved across New England. Because of the less frequent occurrence of New England tropical cyclones, it was necessary to include cases back to 1938 to obtain a reasonable sample size. In addition, because of the faster translational speed and the fairly rapid extratropical transition of the higher-latitude cases, it was necessary to estimate the wind speeds at 2-h intervals after landfall, rather than every 6 h, as in the NHC best track. For the model development, the estimates of the maximu...

72 citations

Journal ArticleDOI
TL;DR: In this article, the authors quantify data availability for a coherent detection wind-profiling lidar, namely, the Leosphere Windcube, collocated with a Vaisala CL31 ceilometer.
Abstract: As the wind energy sector continues to grow, so does the need for reliable vertical wind profiles in the assessment of wind resources and turbine performance. In situ instrumentation mounted on meteorological towers can rarely probe the atmosphere across the full span of modern turbine rotor disks, which typically extend from 40 to 120 m above the surface. However, by measuring the Doppler shift of laser light backscattered by particles in the atmosphere, remote sensing lidar is capable of estimating wind speeds and turbulence at several altitudes in this range and above. Consequently, lidar has proven a promising technology for both wind resource assessment and turbine response characterization. The aim of this study is to quantify data availability for a coherent detection wind-profiling lidar—namely, the Leosphere Windcube.To determine situations of suitable data return rates, a Windcube, collocated with a Vaisala CL31 ceilometer, was deployed as part of the Skywatch Observatory at the Universi...

72 citations


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