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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 case study of a long-lasting (60 h) deep radiation fog that took place in December 2009 is presented to obtain a deeper understanding of the dynamic processes governing such persistent fog.
Abstract: The Ebro river basin, in the northeastern part of the Iberian Peninsula in Europe, very often experiences radiation fog episodes in winter that can last for several days. The impact on human activities is high, especially on road and air transportation. The installation in July 2009 of a WindRASS in the area, which is able to work in the presence of fog, now allows inspecting the vertical structure of the temperature and wind profiles across the roughly 300-m-thick fog layer. We present a case study of a long-lasting (60 h) deep radiation fog that took place in December 2009 to obtain a deeper understanding of the dynamic processes governing such persistent fog. Field observations of vertical profiles of temperature, wind and turbulent kinetic energy are compared with a high-resolution mesoscale simulation, satellite imagery of fog distribution and observations taken in the area to understand why the fog is so persistent and how it dissipates only for a short period in the afternoon despite intermittent turbulence within the fog deck. The confinement of the fog inside a practically closed basin allows us to study the relevant physical processes in the establishment and subsequent evolution of the fog episode using a limited-area mesoscale model. The contribution of the WindRASS measurements allowed us to validate the numerical simulations, particularly inspecting the role of turbulence that can link the bottom and top of the fog through moderate episodic mixing. The fog layer has very weak winds inside, but is well mixed and experiences intermittent top-bottom turbulence generated in its upper part by convection due to radiative cooling and by wind shear due to the topographically generated flows that blow just above the top of the fog.

59 citations

01 Jan 2010
TL;DR: In this paper, the authors extended the previous study of helicity, CAPE, and shear in Hurricane Bonnie (1998) to all eight tropical cyclones sampled by NASA during the Convection and Moisture Experiments (CAMEX).
Abstract: The previous study of helicity, CAPE, and shear in Hurricane Bonnie (1998) was extended to all eight tropical cyclones sampled by NASA during the Convection and Moisture Experiments (CAMEX). Storms were categorized as having large or small ambient vertical wind shear, with 10 m s 21 as the dividing line. In strongly sheared storms, the downshear mean helicity exceeded the upshear mean by a factor of 4. As in the previous study, the helicity differences resulted directly from the tropical cyclone response to ambient shear, with enhanced in-up-out flow and veering of the wind with height present downshear. CAPE in strongly sheared storms was 60% larger downshear. Mean inflow near the surface and the depth of the inflow layer each were 4times largerdownshear.At more than30% of observationpoints outsidethe 100-kmradius in the downshear right quadrant, midlatitude empirical parameters indicated a strong likelihood of supercells. No such points existed upshear in highly sheared storms. Much smaller upshear‐downshear differences and little likelihood of severe cells occurred in storms with ambient wind shear below 10 m s 21 . In addition to these azimuthal asymmetries, highly sheared storms produced 30% larger area-averaged CAPE and double the area-averaged helicity versus relatively unsheared storms. The vortex-scale increase in these quantities lessens the negative impact of large vertical wind shear.

59 citations

Journal ArticleDOI
TL;DR: In this article, an actively controlled wind tunnel for simulating the atmospheric boundary layer is described, where air flows are generated by 99 frequency-controlled fans arranged in a 9 wide by 11 high matrix.

59 citations

Journal ArticleDOI
01 May 2002-Catena
TL;DR: In this paper, a wind tunnel study under wind-driven rains was conducted to determine the combined effect of rain and wind on the rainsplash transport process, and the transport rates were measured by trapping the splashed particles at set distances in the upslope and downslope directions, respectively.
Abstract: A wind tunnel study under wind-driven rains was conducted to determine the combined effect of rain and wind on the rainsplash transport process. The rains driven by horizontal wind velocities of 6, 10 and 12 m s−1 were applied to three agricultural soils packed into a 20×55-cm soil pan placed at both windward and leeward slopes of 4.0°, 8.5° and 11.3°. Transport rates were measured by trapping the splashed particles at set distances in the upslope and downslope directions, respectively, for windward and leeward slopes. Rainsplash transport under wind-driven rains was adequately described (R2=0.93) by relating the transport rate to the rain impact pressure and wind shear velocity by log–linear regression technique. Average trajectory of a raindrop-induced and wind-driven particle was also adequately predicted by the momentum loss per unit time per unit length of travel (u*2/g). The travel distance is found to be three times greater than the path of a typical saltating sand grain.

59 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the High Resolution Dynamics Limb Sounder (HIRDLS) satellite instrument to derive gravity wave momentum fluxes and gravity wave drag in order to investigate the interaction of gravity waves with the SAO.
Abstract: . It is known that atmospheric dynamics in the tropical stratosphere have an influence on higher altitudes and latitudes as well as on surface weather and climate. In the tropics, the dynamics are governed by an interplay of the quasi-biennial oscillation (QBO) and semiannual oscillation (SAO) of the zonal wind. The QBO is dominant in the lower and middle stratosphere, and the SAO in the upper stratosphere/lower mesosphere. For both QBO and SAO the driving by atmospheric waves plays an important role. In particular, the role of gravity waves is still not well understood. In our study we use observations of the High Resolution Dynamics Limb Sounder (HIRDLS) satellite instrument to derive gravity wave momentum fluxes and gravity wave drag in order to investigate the interaction of gravity waves with the SAO. These observations are compared with the ERA-Interim reanalysis. Usually, QBO westward winds are much stronger than QBO eastward winds. Therefore, mainly gravity waves with westward-directed phase speeds are filtered out through critical-level filtering already below the stratopause region. Accordingly, HIRDLS observations show that gravity waves contribute to the SAO momentum budget mainly during eastward wind shear, and not much during westward wind shear. These findings confirm theoretical expectations and are qualitatively in good agreement with ERA-Interim and other modeling studies. In ERA-Interim most of the westward SAO driving is due to planetary waves, likely of extratropical origin. Still, we find in both observations and ERA-Interim that sometimes westward-propagating gravity waves may contribute to the westward driving of the SAO. Four characteristic cases of atmospheric background conditions are identified. The forcings of the SAO in these cases are discussed in detail, supported by gravity wave spectra observed by HIRDLS. In particular, we find that the gravity wave forcing of the SAO cannot be explained by critical-level filtering alone; gravity wave saturation without critical levels being reached is also important.

59 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023155
2022347
2021165
2020157
2019187
2018165