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 article, an increase in the intensity of pre-monsoon tropical cyclones over the Arabian Sea is observed over the last few decades, which is associated with epochal variability in the storm-ambient vertical wind shear and tropical cyclone heat potential.
51 citations
24 May 2017
TL;DR: In this paper, a model-fitting wind field reconstruction technique is applied to nacelle lidar measurements taken at multiple distances close to the rotor, where a wind model is combined with a simple induction model.
Abstract: . Profiling nacelle lidars probe the wind at several heights and several distances upstream of the rotor. The development of such lidar systems is relatively recent, and it is still unclear how to condense the lidar raw measurements into useful wind field characteristics such as speed, direction, vertical and longitudinal gradients (wind shear). In this paper, we demonstrate an innovative method to estimate wind field characteristics using nacelle lidar measurements taken within the induction zone. Model-fitting wind field reconstruction techniques are applied to nacelle lidar measurements taken at multiple distances close to the rotor, where a wind model is combined with a simple induction model. The method allows robust determination of free-stream wind characteristics. The method was applied to experimental data obtained with two different types of nacelle lidar (five-beam Demonstrator and ZephIR Dual Mode). The reconstructed wind speed was within 0.5 % of the wind speed measured with a mast-top-mounted cup anemometer at 2.5 rotor diameters upstream of the turbine. The technique described in this paper overcomes measurement range limitations of the currently available nacelle lidar technology.
51 citations
TL;DR: In this paper, the authors investigated the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather summertime conditions using the numerical model ARPS.
Abstract: This contribution investigates the nature of turbulent kinetic energy (TKE) in a steep and narrow Alpine valley under fair-weather summertime conditions. The Riviera Valley in southern Switzerland was chosen for a detailed case study, in which the evaluation of aircraft data (obtained from the MAP-Riviera field campaign) is combined with the application of high-resolution (350-m horizontal grid spacing) large-eddy simulations using the numerical model ARPS. The simulations verify what has already been observed on the basis of measurements: TKE profiles scale surprisingly well if the convective velocity scale w* is obtained from the sun-exposed eastern slope rather than from the surface directly beneath the profiles considered. ARPS is then used to evaluate the TKE-budget equation, showing that, despite sunny conditions, wind shear is the dominant production mechanism. Therefore, the surface heat flux (and thus w*) on the eastern slope does not determine the TKE evolution directly but rather, as we believe, indirectly via the interaction of thermally-driven cross-valley and along-valley flows. Excellent correlation between w* and the up-valley wind speed solidifies this hypothesis.
51 citations
TL;DR: In this article, a decision threshold was developed at the National Severe Storms Laboratory to discriminate between mesocyclone shear and other shears not associated with organized circulatory flow, and a detailed test of these and other thresholds was made by testing the algorithm on storms with and without mesocyclones.
Abstract: A region of high wind shear always accompanies large intense tornadoes. Such shear is readily measured by Doppler radar and thus can be used to identify regions in storms where tornadoes are likely to form. An algorithm developed at the National Severe Storms Laboratory uses decision thresholds to discriminate between mesocyclone shear and other shears not associated with organized circulatory flow. A detailed test of these and other thresholds was made by testing the algorithm on storms with and without mesocyclones. The algorithm requires storage and calculations on two consecutive radials of data, and thus is suitable for real time implementation. We have applied the algorithm to data from sixteen mesocyclones to evaluate detection performance. The probability of false alarm was 10%, and the probability of detection was 90%. The algorithm accounts for distortion of the shear pattern caused by the large antenna beam dimensions at long ranges.
51 citations
TL;DR: In this article, field observations were conducted on a natural, open ocean beach system in Japan to investigate characteristics of wind-blown sand transport under various weather conditions including a storm event, and the 5-min mean wind velocity/impact counts relationship was well constrained by both second-and third-order polynomial fitting of velocity under similar weather conditions.
Abstract: [1] Field observations were conducted on a natural, open ocean beach system in Japan to investigate characteristics of wind-blown sand transport under various weather conditions including a storm event. Data sets over periods of several hours included blown sand impact counts, three-dimensional wind conditions, hourly precipitation, and moisture content of the sediment surface. The intermittent blown sand impact data shifted by 1 s ahead of the wind velocity correlated with the wind velocity during a no-rainfall period (for an assumed dry surface) and in the longshore wind direction (for sufficiently long fetch length). The 5-min mean wind velocity/impact counts relationship was well constrained by both second- and third-order polynomial fitting of velocity under similar weather conditions. During a no-rainfall period and in the longshore wind direction, the relationship between the wind velocity and sand flux estimated from the counts coincides with existing studies in wind tunnel experiments. The sand flux, however, decreased by 1 order of magnitude because of a change in the wind direction from longshore to cross-shore and then by more than 1 order of magnitude because of an increase in the moisture content. Threshold wind velocity calculated using the time fraction equivalence method with the impact counts and the horizontal wind velocity in 5-min sampling periods was approximately equal to the value predicted using Bagnold's equation during the no-rainfall period and increased significantly during the rainfall phase. The sand flux sensor has several limitations for complex conditions in the field; however, it provides a number of characteristics of sand transport under various meteorological conditions.
51 citations