Wind shear

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

Wind Energy Extraction by Birds and Flight Vehicles

Abstract: When a bird or flight vehicle is oriented with a component of its lift vector aligned with the natural wind work is done on the flight system. Consequently, by suitable maneuvers, variations in wind speed can be used to add energy to the system. These procedures are used by albatrosses and many other birds. The equations of motion are simplified by normalizing using the minimum drag speed and integrating numerically for the control cycles involving angles of attack and bank. An energy neutral cycle by which an un-powered vehicle returns to initial velocity and height depends only upon the maximum lift/drag ratio of the vehicle and the wind speed variation. The minimum speed difference for a neutral energy cycle occurs for a vertical or horizontal step in wind speed. For a continuous wind profile a variational method is used to find the minimum gradient for a neutral energy cycle. Simple expressions are derived for the minimum wind variations for these two cases. The oceanic boundary layer and the shear layer downwind of a ridge are studied, and neutral energy wind criteria derived for them. Birds and small UAVs, with flight speeds comparable to atmospheric wind variations, can profit from wind energy extraction. Presented at the 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno NV, January, 10-13, 2005: Lissaman, P.B.S., “Wind Energy Extraction by Birds and Flight Vehicles,” AIAA Paper 2005-241, AIAA Annual Meeting, Reno, Jan. 2005.

A Three-Dimensional Numerical Model of an Isolated Thunderstorm: Part I. Comparative Experiments for Variable Ambient Wind Shear

Abstract: The mature stage of an isolated convective storm in sheared surroundings is studied by means of an anelastic three-dimensional numerical model. Liquid precipitation and turbulence are included in parameterized form. Three comparative experiments are run with different vertical profiles of ambient wind: no ambient wind, uni-directional shear, and multi-directional shear dominated by strong low-level veering, the first shear profile being the west-east projection of the second. The cases are compared in regard to airflow, pressure, potential temperature and liquid water. The results were as follows: Both sheared storms exhibit a quasi-erect high-speed updraft, a deep cyclonic-anticylonic vortex couplet aloft, middle-level barrier flow around the updraft, and gradual splitting into cyclonic and anti-cyclonic cells moving to the right and left of the mean winds. The model storms show a slightly weaker growing stage with shear than without, but the mature stage is stronger and more persistent. Without...

North Atlantic Wind Waves and Wind Stress Fields from Voluntary Observing Ship Data

Abstract: On the basis of the collection of individual marine observations available from the Comprehensive Ocean–Atmosphere Data Set, major parameters of the sea state were evaluated. Climatological fields of wind waves and swell height and period, as well as significant wave height and resultant period are obtained for the North Atlantic Ocean for the period from 1964 to 1993. Validation of the results against instrumental records from National Data Buoy Center buoys and ocean weather station measurements indicate relatively good agreement for wave height and systematic biases in the visually estimated periods that were corrected. Wave age, which is important for wind stress estimates, was evaluated form wave and wind observations. The climatology of wave age indicates younger waves in winter in the North Atlantic midlatitudes and Tropics. Wave age estimates were applied to the calculations of the wind stress using parameterizations from field experiments. Differences between wave-age-based and traditional estimates are not negligible in wintertime in midlatitudes and Tropics where wave-induced stress contributes from 5% to 15% to the total stress estimates. Importance of the obtained effects for ocean circulation and climate variability is discussed.

The effect of wind shear on falling precipitation

Abstract: Precipitation particles which fall from a source aloft through a wind shear are sorted as to size, the largest particles reaching the ground closest to the generating source, the smaller particles further from it. If precipitation is assumed to form continuously in cloud, with a fixed size distribution, this sorting affects significantly the size distributions to be observed below the cloud, and so the relationship between the precipitation rate R and the radar scattering-parameter Z (which is ∑D6, where D is the diameter of a raindrop or the water drop to which a snowflake would melt, and the summation is over unit volume). As an approximation to a small isolated shower, a horizontal generating element has been taken, of linear extent 1.6 kilometers in the direction of the wind shear. The quantities R and Z tend to be less at the ground than in the generating region, the size distributions remaining the same except for upper and lower limits of size imposed by the sorting. Several values of R an...