Wind shear

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

Formation and Diurnal Variation of the Dryline

Abstract: The formation and diurnal evolution of the dryline during fair weather have been investigated through the use of a two-dimensional mesoscale model that includes condensation/evaporation, budget equations of surface energy and moisture field, as well as turbulence and radiation parameterizations.A moderately strong, vertical wind shear was introduced on a sloping terrain, where the soil is very dry on the west side but moist on the east. Initially, a weak easterly geostrophic wind exists to the east but a weak westerly geostrophic wind to the west of the dryline. During daytime, deepening of the mixed layer due to vertical mixing, especially on the west side, forces the dryline to advance eastward. The westerly wind on the west side is maintained by downward transport of westerly momentum due to strong vertical mixing; the easterly wind on the east side is strengthened due to the inland sea-breeze circulation. Therefore, the resulting low-level convergence sustains a strong moisture gradient along...

Sensitivity of Turbine-Height Wind Speeds to Parameters in Planetary Boundary-Layer and Surface-Layer Schemes in the Weather Research and Forecasting Model

Abstract: We evaluate the sensitivity of simulated turbine-height wind speeds to 26 parameters within the Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary-layer scheme and MM5 surface-layer scheme of the Weather Research and Forecasting model over an area of complex terrain. An efficient sampling algorithm and generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of simulated turbine-height wind speeds. The results indicate that most of the variability in the ensemble simulations is due to parameters related to the dissipation of turbulent kinetic energy (TKE), Prandtl number, turbulent length scales, surface roughness, and the von Karman constant. The parameter associated with the TKE dissipation rate is found to be most important, and a larger dissipation rate produces larger hub-height wind speeds. A larger Prandtl number results in smaller nighttime wind speeds. Increasing surface roughness reduces the frequencies of both extremely weak and strong airflows, implying a reduction in the variability of wind speed. All of the above parameters significantly affect the vertical profiles of wind speed and the magnitude of wind shear. The relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability.

On the analysis of wind wave-induced disturbances in the atmospheric turbulent surface layer

Abstract: Simultaneous measurements of wind velocity, air humidity and sea surface wave-elevation fluctuations obtained on a platform in the open Caspian Sea are analyzed. It is shown that wave noises exist in the spectra and cospectra of the lower part of the atmospheric boundary layer, not only for the frequency of the main energy transporting component of the sea waves, but also in other parts of the spectra, at both lower and higher frequencies. The high frequencies are noncoherent with the sea waves and could be considered as measurement ‘errors’ due to the existence of the waves. A method of elimination of the coherent wave noises from the spectra and cospectra is suggested and the effectiveness of its application is demonstrated. The essential difference between cases of developing and decaying wind waves is demonstrated.

Implications of the Hydrostatic Assumption on Atmospheric Gravity Waves

Abstract: The validity of the hydrostatic approximation is examined for use in predicting the dynamics of topographically generated atmospheric gravity waves (lee waves) propagating in an atmosphere with realistic wind shear. To isolate nonhydrostatic effects, linear, analytic solutions derived both with and without the hydrostatic assumption are compared. The atmospheric profiles of wind and stability are chosen both to render the governing equations analytically tractable and be representative of typical atmospheric conditions. Two atmospheric models are considered: 1) a troposphere-only model in which the wind increases linearly with height and the stability is constant and 2) a troposphere-stratosphere model, which retains the important effect of the vertical wind shear in the troposphere and adds the essential feature of a stability jump at the tropopause. The nonhydrostatic trapping effect of wind shear on gravity wave modes is clearly illustrated in the troposphere-only atmospheric model. In the tro...