Wind shear

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

Wind Speeds as Measured by Cup and Sonic Anemometers and Influenced by Tower Structure

Abstract: Wind tunnel and field experiments have shown that the fast-response three-component sonic anemometer is a highly accurate wind speed sensor. When sonic anemometers were used as reference sensors for wind speed, slower response cup anemometers were found to consistently overestimate the wind speed. Despite measures taken during a field program in Kansas to minimize tower influence on wind measurements, the errors due to the tower effect on the windward side are inferred to be about ±5% of the observed wind speed ratios of cup to sonic anemometers. When the observed speed ratios are compared with the errors due to tower influence, the overspeeding of the cup anemometer is estimated to be about 10% of the reference wind speed.

Orographic shaping of US West Coast wind profiles during the upwelling season

Abstract: Spatial and temporal variability of nearshore winds in eastern boundary current systems is affected by orography, coastline shape, and air-sea interaction These lead to a weakening of the wind close to the coast: the so-called wind drop-off In this study, regional atmospheric simulations over the US West Coast are used to demonstrate monthly characteristics of the wind drop-off and assess the mechanisms controlling it Using a long-term simulation, we show the wind drop-off has spatial and seasonal variability in both its offshore extent and intensity The offshore extent varies from around 10 to 80 km from the coast and the wind reduction from 10 to 80 % We show that when the mountain orography is combined with the coastline shape of a cape, it has the biggest influence on wind drop-off The primary associated processes are the orographically-induced vortex stretching and the surface drag related to turbulent momentum flux divergence that has an enhanced drag coefficient over land Orographically-induced tilting/twisting can also be locally significant in the vicinity of capes The land-sea drag difference acts as a barrier to encroachment of the wind onto the land through turbulent momentum flux divergence It turns the wind parallel to the shore and slightly reduces it close to the coast Another minor factor is the sharp coastal sea surface temperature front associated with upwelling This can weaken the surface wind in the coastal strip by shallowing the marine boundary layer and decoupling it from the overlying troposphere

Southwesterly flows over southern Norway—mesoscale sensitivity to large-scale wind direction and speed

Abstract: Mesoscale structures have been identified and studied for simulations of ideal flows passing southern Norway. The large-scale wind direction was between south and west and the wind speed between 10 and 22.5 m s −1 . Flow data have been provided from simulations with a mesoscale numerical model with 10 km between the grid points horizontally. The results are found to be qualitatively in accordance with observational findings, including old forecasting rules for southern Norway. As expected, the influence of rotation is considerable. Accordingly, the flows are characterized by a jet on the left side of the mountains and a minimum on the right upstream side. In addition, a wind shadow extends far downstream of the main mountains, with signs of increased winds on the right side of the wind shadow. The wind shadow is connected to an inertio-gravity wave with downstream signatures caused by rotation. When the background wind direction was turned, the alignment of the structures was turned accordingly. For flows in the sector 200–270°, the action of the Coriolis force gave an efficiently narrower mountain (than without rotation). A similar action for southerly flows, on the other hand, resulted in an efficiently wider mountain. Different mountain widths resulted in different shape of the gravity waves and different acceleration of the jet on the left side. When the wind speed is increased, the amplitudes of the mesoscale structures are decreased with no abrupt change in the character of the flow.

Kelvin-Helmholtz instability around the tropical tropopause observed with the Equatorial Atmosphere Radar

Abstract: [1] In November 2001, the Equatorial Atmosphere Radar (0.20°S, 100.32°E) observed a continuous strong eastward wind shear (10–50 m s−1 km−1), westward wind (2–27 m s−1), and the radar echo layer tilted downward to the west in the region 0–1 km above the tropopause. During the same period, the Richardson number calculated with hourly-averaged horizontal wind and radiosonde temperature data was almost continuously <0.5 and sometimes <0.25, which seems to indicate that the Kelvin-Helmholtz instability (KHI) frequently occurs in that region. The existence of the tilted radar echo layer can be explained by KHI billows. A spurious updraft caused by the KHI-induced tilted echo layer and by the strong westward wind was also observed in the region.