Wind shear

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

Effects of Vertical Wind Shear on Tropical Cyclone Precipitation

Abstract: The response of the precipitation field for tropical cyclones in relation to the surrounding environmental vertical wind shear has been investigated using ∼20 000 snapshots of passive-microwave satellite rain rates. Composites of mean rain rates, 95th percentile rain rates, and rain coverage were constructed to compare how the spatial distribution of the precipitation was organized under varying environmental shear. Results indicated that precipitation is displaced downshear and to the left (right for Southern Hemisphere) of the shear vector. The amplitude of this displacement increases with stronger shear. The majority of the asymmetry found in the mean rain rates is accounted for by the asymmetry in the occurrence of heavy rain. Although rain is common in all quadrants of the sheared tropical cyclones, heavy rain (≥8 mm h−1 at the ∼25-km scale) is comparatively rare in the upshear-right quadrant. It is shown that the effect that shear has on the rain field is nearly instantaneous. Strong wester...

Local mean state changes due to gravity wave breaking modulated by the diurnal tide

Abstract: During gravity wave breaking, heating rates are determined by wave advection, turbulent diffusion, and turbulence dissipative heating. A series of numerical experiments show that the total heating rates can be larg (∼ ±10 Kh−1) and can cause large local temperature changes. The wave advection causes dynamical cooling in most of the wave breaking region, consistent with previous studies. Nonuniform vertical turbulent diffusion causes strong transient heating in the lower part of the wave breaking region and cooling above. The dissipative heating rate is relatively small compared with those due to the dynamical cooling and turbulent diffusion. In these numerical experiments, zonal wind and temperature perturbations of the diurnal tide and the zonal mean zonal wind and temperature compose the background state for the computation. This is used to examine the idea that temperature inversions, often observed in the mesosphere, are related to the gravity wave and tidal wave interactions. The simulation results show that the large temperature changes in this process can form temperature inversion layers that progress downward with a speed similar to that of a diurnal tide phase speed, which clearly suggests the tidal modulation of the gravity wave and mean flow interactions. Such a process is dependent on season and latitude, because the background state stability varies with season and latitude. The development of the temperature inversion is also affected by the gravity wave characteristics. It is also shown that the local mean wind, wind shear, and chemical species can undergo large changes accompanying the temperature inversion.

Lidar Investigation of Atmosphere Effect on a Wind Turbine Wake

Abstract: An experimental study of the spatial wind structure in the vicinity of a wind turbine by a NOAA coherent Doppler lidar has been conducted. It was found that a working wind turbine generates a wake with the maximum velocity deficit varying from 27% to 74% and with the longitudinal dimension varying from 120 up to 1180 m, depending on the wind strength and atmospheric turbulence. It is shown that, at high wind speeds, the twofold increase of the turbulent energy dissipation rate (from 0.0066 to 0.013 m2 s−3) leads, on average, to halving of the longitudinal dimension of the wind turbine wake (from 680 to 340 m).

Influence of atmospheric stability on wind turbine power performance curves

Abstract: The impact of atmospheric stability on vertical wind profiles is reviewed and the implications for power performance testing and site evaluation are investigated. Velocity, temperature, and turbulence intensity profiles are generated using the model presented by Sumner and Masson. This technique couples Monin-Obukhov similarity theory with an algebraic turbulence equation derived from the k-e turbulence model to resolve atmospheric parameters u*, L, T*, and Zo. The resulting system of nonlinear equations is solved with a Newton-Raphson algorithm. The disk-averaged wind speed u disk is then evaluated by numerically integrating the resulting velocity profile over the swept area of the rotor. Power performance and annual energy production (AEP) calculations for a Vestas Windane-34 turbine from a wind farm in Delabole, England, are carried out using both disk-averaged and hub height wind speeds. Although the power curves generated with each wind speed definition show only slight differences, there is an appreciable impact on the measured maximum turbine efficiency. Furthermore, when the Weibull parameters for the site are recalculated using u disk, the AEP prediction using the modified parameters falls by nearly 5% compared to current methods. The IEC assumption that the hub height wind speed can be considered representative tends to underestimate maximum turbine efficiency. When this assumption is further applied to energy predictions, it appears that the tendency is to overestimate the site potential.