Topic
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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TL;DR: In this paper, a model for evaluating the effectiveness of a barrier for reducing the capacity of local wind to cause erosion is presented. But, the model assumes that wind shear forces on the soil surface exceed the soil's resistance to those forces, soil particles detach and are transported by the wind.
Abstract: WHEN wind shear forces on the soil surface exceed the soil's resistance to those forces, soil particles detach and are transported by the wind. Barriers ob-struct the wind and reduce the wind's speed, thus, reducing wind erosion. Application of a model, developed for evaluating ef-fectiveness of a barrier for reducing the capacity of local wind to cause erosion, illustrated: (a) Wind erosion forces are reduced more than windspeed. (b) Properly oriented barriers give much more protection when pre-ponderance of wind erosion forces in prevailing wind erosion direction is high than when preponderance is low. (c) When preponderance of wind erosion forces is low, barrier orientation is almost inconsequential. (d) Because of seasonal variation of wind direction and speed, need for and amount of protection also vary seasonally. Many trees, shrubs, tall growing crops, and grasses, and slat-fences all can be used as barriers to reduce wind erosion.
53 citations
TL;DR: In this article, the turbulent temperature structure and winds in thermal convective plumes over prairie grassland have been investigated with an acoustic echo sounder system, where three spaced acoustic antennas, with two inclined at 45° elevation, were used to provide plume shape information and Doppler-derived total wind vector patterns between heights of 70 and 500 m.
Abstract: The turbulent temperature structure and winds in thermal convective plumes over prairie grassland have been investigated with an acoustic echo sounder system. Three spaced acoustic antennas, with two inclined at 45° elevation, were used to provide plume shape information and Doppler-derived total wind-vector patterns between heights of 70 and 500 m. Supporting in situ measurements were made on a 15 m tower, with a tethered balloon-supported Boundary Layer Profiler, and from a light aircraft. The most probable orientation of the plumes was nearly vertical, but frequent upwind and downwind tilts were also observed. Maximum positive vertical velocities in the plumes at midday were near 2 m s−1, while maximum downward currents were one-half this value. Acoustic echoes from regions above the mixed layer, corresponding in height to an elevated temperature inversion, correlate well with regions of maximum wind shear.
53 citations
TL;DR: In this article, the use of ground-based clear-air Doppler radars to observe the structure of elevated atmospheric layers and associated flux quantities is described, and case studies in which radar and balloon data were available were analyzed.
Abstract: The use of ground-based clear-air Doppler radars to observe the structure of elevated atmospheric layers and associated flux quantities is described. Case studies in which radar and balloon data were available are analyzed. Doppler second-moment (velocity variance) data are used to calculate turbulent kinetic energy dissipation rate ϵ. Velocity variance, refractive index structure parameter and wind shear are used to estimate the refractive index gradient across elevated weather-frontal interfaces. A case is analyzed in which both acoustic-sounder and radar-sounder data are available, so profiles of structure parameter of both temperature and humidity can be deduced and used to calculate the fluxes of heat and moisture within the frontal interface. The fluxes deduced from radar data are compared with corresponding in situ measurements made by aircraft in other geographical regions. The relationship between the turbulent Prandtl number and the Richardson number emerges as very important to the gen...
53 citations
TL;DR: In this paper, the authors used a three-dimensional cloud-resolving model to investigate the impact of circulations driven by tropical tropopause layer (TTL) radiative heating on the cloud evolution.
Abstract: [1] Thin cirrus that frequently form in the tropical tropopause layer (TTL) are important for vertical transport through the TTL, regulation of stratospheric humidity, and the Earth's radiation budget. Here, we use a three-dimensional cloud-resolving model to investigate the impact of circulations driven by TTL cirrus radiative heating on the cloud evolution. We use observations of TTL environmental conditions (thermal stability and wind shear) and TTL cirrus microphysical properties (ice crystal sizes and concentrations) to constrain the simulations. We show that with ice crystal sizes consistent with available observations (effective radii ≥ 12 μm), typical thermal stability, and moderate wind shear, the ice cloud sediments to lower levels before radiative heating can drive a circulation to maintain the cloud and before small-scale convection builds up. In this case, the cloud lifetime is controlled by sedimentation of ice crystals into subsaturated air below the initial cloud level, followed by sublimation. Strong wind shear (>10 m s−1 km−1) tends to hasten the cloud dissipation. With relatively weak thermal stability, small-scale convection builds up rapidly, resulting in mixing at cloud top and extension of the cloud lifetime. We also consider the impact of synoptic-scale and mesoscale temperature variability on cloud lifetime. Using TTL trajectories with small-scale wave temperature perturbations superimposed, we show that TTL cirrus will often dissipate within 12–24 h simply as a result of background temperature variability.
53 citations
TL;DR: In this paper, the authors compared three different methods for determining overlake wind speed as a function of overland wind speed and the difference between overland air temperature and water temperature.
53 citations