On nocturnal wind shear with a view to engineering applications

Wittich, Klaus-Peter; Hartmann, Jörg; Roth, Rainer

doi:10.1007/bf00122985

Cited by 12 publications

(11 citation statements)

References 6 publications

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“…In most cases, the results of validation of mesoscale models against observations revealed that strong near‐surface winds resulted in warm biases in near‐surface temperatures in nighttime CAPs and vice versa (Chiao & Dumais, ; Lee et al, ). An accurate simulation of boundary layer processes affected by LLJs has substantial practical value for transport of urban pollutants, wind power industry, and aviation safety in Yerevan (Storm et al, ; Wittich et al, ).…”

Section: Introductionmentioning

confidence: 99%

A Case Study of Low‐Level Jets in Yerevan Simulated by the WRF Model

Gevorgyan

2018

JGR Atmospheres

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Capabilities of high‐resolution (3 km) Weather Research and Forecasting (WRF) simulations to reproduce topographically induced mountain‐valley winds and low‐level jets (LLJs) in Yerevan have been evaluated using high‐frequency observational and modeled data. High sensitivities of simulations of near‐surface winds and LLJ characteristics observed on 4 July 2015 to both boundary layer and initial and lateral boundary conditions setup have been demonstrated. Among the nine tested planetary boundary layer (PBL) parameterization schemes the MYJ, QNSE, and TEMF PBL schemes showed greater skill in simulation of near‐surface valley winds over Yerevan, while the other PBL schemes tend to significantly underestimate the strength of valley winds, with the BouLac PBL scheme being the worst performer. Most of PBL schemes simulate well‐defined LLJs in Yerevan associated with evening valley winds. The simulated jet cores are mostly located between 150 and 250 m above ground with magnitudes varying from 12 to 21 m s−1. However, the intensity of the observed nocturnal LLJ in Yerevan (located at 110 m above ground) is strongly underestimated by most of the WRF runs while the Shin and Hong and YSU PBL schemes simulate nocturnal LLJs higher than the observed LLJ. The WRF runs initiated with newly released European Centre for Medium‐Range Weather Forecasts ERA‐5 data set showed improved simulation of near‐surface winds and nighttime potential temperatures in Yerevan relative to those forced by the Global Forecast System fields.

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Section: Introductionmentioning

confidence: 99%

A Case Study of Low‐Level Jets in Yerevan Simulated by the WRF Model

Gevorgyan

2018

JGR Atmospheres

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“…The nocturnal LLJ is an important mechanism for atmospheric mixing and transport (Stensrud, ) with a large potential to affect aviation (Wittich et al, ), air quality (McNider et al, ; Mao and Talbot, ; Darby et al, ), and the wind energy industry (Storm et al, ). Observational and modelling studies in recent years have indicated that the nocturnal LLJ also plays an important role in the emission and transport of Saharan mineral dust (Knippertz and Todd, ).…”

Section: Introductionmentioning

confidence: 99%

Idealized large‐eddy simulations of nocturnal low‐level jets over subtropical desert regions and implications for dust‐generating winds

Heinold

Knippertz

Beare

2014

Quart J Royal Meteoro Soc

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Nocturnal low-level jets (LLJs) are maxima in the wind profile, which often form above the stable nocturnal boundary layer. Over the Sahara, the world's largest source of mineral dust, this phenomenon is of particular importance to the emission and transport of desert aerosol. We present the first ever detailed large-eddy simulations of dust-generating Combining the functional relationships with high-resolution roughness data over northern Africa gives good agreement with the location of morning dust uplift in satellite observations. It is shown that shear-induced mixing plays an important role for the LLJ evolution and surface gustiness. With decreasing latitude the LLJ oscillation period is longer and, thus, shearinduced mixing is weaker, allowing a more stable nocturnal stratification to develop. This causes a later and more abrupt LLJ breakdown in the morning with stronger gusts, which can compensate for the slower LLJ evolution that leads to a weaker jet maximum. The findings presented here can serve as the first step towards a parametrization to improve the representation of the effects of nocturnal LLJs on dust emission in coarser-resolution models.

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“…The LLJ is a phenomenon typically confined to a vertical wind band of 50 to 200 m thickness (see examples in the studies of Wittich et al , Baas et al , and Prabha et al ) that has been observed and described theoretically for six decades . For some airports with a frequent occurrence of LLJ and high wind speed up to 15 m s −1 , the LLJ is included in forecasts to alert aircraft in the phase of takeoff and landing, where the occurrence of unexpected and strong wind shear and changes of wind direction can be dangerous …”

Section: Introductionmentioning

confidence: 99%

“…In the surroundings of Braunschweig, Germany, the LLJ has beed studied experimentally and numerically by different authors . Typical LLJ events had the wind speed maximum at an altitude around 200 m .…”

Section: Introductionmentioning

confidence: 99%

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One-year observations of the wind distribution and low-level jet occurrence at Braunschweig, North German Plain

et al. 2015

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A data set consisting of one-year vertical profiles of horizontal wind speed obtained with lidar at Braunschweig Airport, North German Plain, is analyzed with respect to the low-level jet (LLJ). The observations reveal a typical LLJ altitude between 80 and 360 m, a frequency of occurrence up to almost 9% for some altitudes, and a typical wind speed between 4 and 9 m s À1 . LLJ events occurred most frequently in summer during the night. In the winter, LLJs were observed both during day and night. The Weibull distribution for wind speed is presented for different heights. The most probable wind speed of the Weibull distribution increases from 4 m s À1 at 40 m altitude to values exceeding 7 m s À1 for altitudes above 240 m. There is a significant difference for the Weibull parameters determined with a monthly, seasonal and annual data set. The contribution of the LLJ to the overall wind speed distribution is analyzed. An LLJ event occurred on 52% of the days over the year, with a total measurement time of 739 h. As the typical rated speed for onshore wind turbines is in the range from 11.5 to 14.5 m s À1 and the typical hub height is in the range of 100 to 150 m, it can be expected that wind turbines are affected by the LLJ.

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On nocturnal wind shear with a view to engineering applications

Cited by 12 publications

References 6 publications

A Case Study of Low‐Level Jets in Yerevan Simulated by the WRF Model

A Case Study of Low‐Level Jets in Yerevan Simulated by the WRF Model

Idealized large‐eddy simulations of nocturnal low‐level jets over subtropical desert regions and implications for dust‐generating winds

One-year observations of the wind distribution and low-level jet occurrence at Braunschweig, North German Plain

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