Wind shear

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

Large eddy simulation study of scalar transport in fully developed wind-turbine array boundary layers

Abstract: Wind harvesting is fast becoming an important alternative source of energy As wind farms become larger, they begin to attain scales at which two-way interactions with the atmospheric boundary layer (ABL) must be taken into account Several studies have shown that there is a quantifiable effect of wind farms on the local meteorology, mainly through changes in the land-atmosphere fluxes of heat and moisture In particular, the observed trends suggest that wind farms increase fluxes at the surface and this could be due to increased turbulence in the wakes Conversely, simulations and laboratory experiments show that underneath wind farms, the friction velocity is decreased due to extraction of momentum by the wind turbines, a factor that could decrease scalar fluxes at the surface In order to study this issue in more detail, a suite of large eddy simulations of an infinite (fully developed) wind turbine array boundary layer, including scalar transport from the ground surface without stratification, is performed Results show an overall increase in the scalar fluxes of about 10%–15% when wind turbines are present in the ABL, and that the increase does not strongly depend upon wind farm loading as described by the turbines’ thrust coefficient and the wind turbines spacings A single-column analysis including scalar transport shows that the presence of wind farms can be expected to increase slightly the scalar transport from the bottom surface and that this slight increase is due to a delicate balance between two strong opposing trends

The Seasat-A satellite scatterometer - The geophysical evaluation of remotely sensed wind vectors over the ocean

Abstract: A description is given of the algorithm used to convert Seasat-A satellite microwave scatterometer measurements of ocean normalized radar cross section to the neutral stability vector wind at 19.5 m height, as well as to compare these winds with high-quality surface observations. The wind vector algorithm used an empirical normalized radar cross section model function to describe the ocean normalized radar cross section's dependence on the 19.5-m neutral stability wind vector. In addition, two model functions were evaluated by means of an independent set of in situ surface wind observations from the Joint Air Sea Interaction experiment (JASIN). Better results were produced by these comparisons than the stipulated Seasat wind speed and direction accuracy specifications of + or - 2 m/sec and + or - 20 deg, respectively, over the 0-16 m/sec range of winds observed during JASIN.

The Physics of the Marine Stratocumulus-Capped Mixed Layer.

Abstract: In order to simulate the stratocumulus-capped mixed layer, a one-dimensional stratocumulus model is developed. This model consists of five major points: 1) a one-dimensional (1D) option of the CSU Cloud/Mesoscale Model, 2) a partially diagnostic higher-order turbulence model, 3) an atmospheric radiation model, 4) a partial condensation parameterization, and 5) the drizzle process. This model is tested against the observed structure of the marine stratocumulus layer reported by Brost et al. In this paper we also investigate the interactions among the following physical processes: atmospheric radiation, cloud microphysics, vertical wind shear, turbulent mixing, large-scale divergence, the sea surface temperature and the presence of high-level clouds above the capping inversion. The model simulated fields were found to be in generally good agreement with observations, although the amount of cloud liquid water predicted was too large. This may have been a result of employing a wind profile that exhib...

Microburst Wind Structure and Evaluation of Doppler Radar for Airport Wind Shear Detection

Abstract: The horizontal and vertical structure of airflow within microbursts has been determined using Doppler weather radar data from the Joint Airport Weather Studies (JAWS) Project. It is shown that the downdraft typically associated with microbursts is about 1 km wide and begins to spread horizontally at a height below 1 km. The median time from initial divergence at the surface to maximum differential wind velocity across the microburst is five minutes. The height of maximum differential velocity is about 75 m, and the median velocity differential is 22 m/s over an average distance of 3.1 km. The outflow of the air is asymmetric, averaging twice as strong along the maximum axis compared to the mininum axis. Some technical requirements for a radar system to detect microbursts and to provide aircraft with early warnings of the onset of windshear are identified.

The GISS Global Climate-Middle Atmosphere Model. Part I: Model Structure and Climatology

Abstract: The GISS global climate model (Hansen et al.) has been extended to include the middle atmosphere up to an altitude of approximately 85 km. The model has the full array of processes used for climate research, i.e., numerical solutions of the primitive equations, calculation of radiative and surface fluxes, a complete hydrologic cycle with convective and cloud cover parameterizations, etc. In addition, a parameterized gravity wave drag formulation has been incorporated, in which gravity-wave momentum fluxes due to flow over topography, wind shear and convection are calculated at each grid box, using theoretical relationships between the grid-scale variables and expected source strengths. The parameterized waves then propagate vertically upward depending on the instantaneous wind and temperature profiles, with waves breaking at levels in which their momentum flux exceed the background saturation value. Radiative damping is also calculated, and the total momentum convergence in each layer is used to ...