Evidence for Gap Flows in the Birch Creek Valley, Idaho

Abstract A field study was conducted of flows in the Birch Creek Valley in eastern Idaho. There is a distinct topographic constriction in the Birch Creek Valley that creates two subbasins: an upper and lower valley. The data were classified into one of three groups based on synoptic influence (weak/absent, high wind speeds, and other evidence of synoptic influence). Gap flows commonly developed downwind of the constriction in association with the weak/absent group but also occurred in association with the two synoptic groups suggesting the potential for more diverse origins. In general, the frequency and strength of gap flows appeared to be linked to the development of the requisite thermal regime and minimization of any synoptically driven southerly winds that would suppress outflows. Gap flows were characterized by high wind speeds with jetlike vertical profiles along the axis of the lower valley. For all three groups the morning transition in the upper valley and western sidewall usually proceeded slightly ahead of the lower valley, consistent with the principles of the topographic amplification factor. The persistence of southerly winds in the lower valley past evening transition inhibited the development of gap flows, promoted strong nighttime inversions, and delayed the onset of morning transition relative to the upper valley. Nocturnal temperature inversions in the lower valley were largely eliminated with the onset of strong gap flows resulting in earlier morning transitions there. The form for a method of predicting gap flow wind speeds is proposed.

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Seasonal Variability in the Diurnal Evolution of the Boundary Layer in a Near-Coastal Urban Environment

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-11-00114.1 ◽

2012 ◽

Vol 29 (5) ◽

pp. 697-710 ◽

Cited By ~ 50

Author(s):

Christine L. Haman ◽

Barry Lefer ◽

Gary A. Morris

Keyword(s):

Boundary Layer ◽

Surface Layer ◽

Vertical Profiles ◽

High Wind ◽

Layer Height ◽

Boundary Layer Height ◽

Wind Speeds ◽

Early Evening ◽

Stable Surface Layer

Abstract Boundary layer height is estimated during a 21-month period in Houston, Texas, using continuous ceilometer observations and the minimum-gradient method. A comparison with over 60 radiosondes indicates overall agreement between ceilometer- and radiosonde-estimated PBL and residual layer heights. Additionally, the ceilometer-estimated PBL heights agree well with 31 vertical profiles of ozone. Difficulty detecting the PBL height occurs immediately following a frontal system with precipitation, during periods with high wind speeds, and in the early evening when convection is weakening, a new stable surface layer is forming, and the lofted aerosols detected by the lidar do not represent the PBL. Long-term diurnal observations of the PBL height indicate nocturnal PBL heights range from approximately 100 to 300 m throughout the year, while the convective PBL displays more seasonal and daily variability typically ranging from 1100 m in the winter to 2000 m in the summer.

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Gap Flows through Idealized Topography. Part I: Forcing by Large-Scale Winds in the Nonrotating Limit

Journal of the Atmospheric Sciences ◽

10.1175/jas-3340.1 ◽

2004 ◽

Vol 61 (23) ◽

pp. 2846-2862 ◽

Cited By ~ 35

Author(s):

Saša Gaberšek ◽

Dale R. Durran

Keyword(s):

Large Scale ◽

Vertical Motion ◽

High Wind ◽

Mountain Wave ◽

Wave Regime ◽

Wind Speeds ◽

Bernoulli’S Equation ◽

Gap Flow ◽

Bernoulli Function ◽

Strong Winds

Abstract Gap winds produced by a uniform airstream flowing over an isolated flat-top ridge cut by a straight narrow gap are investigated by numerical simulation. On the scale of the entire barrier, the proportion of the oncoming flow that passes through the gap is relatively independent of the nondimensional mountain height ε, even over that range of ε for which there is the previously documented transition from a “flow over the ridge” regime to a “flow around” regime. The kinematics and dynamics of the gap flow itself were investigated by examining mass and momentum budgets for control volumes at the entrance, central, and exit regions of the gap. These analyses suggest three basic behaviors: the linear regime (small ε) in which there is essentially no enhancement of the gap flow; the mountain wave regime (ε ∼ 1.5) in which vertical mass and momentum fluxes play a crucial role in creating very strong winds near the exit of the gap; and the upstream-blocking regime (ε ∼ 5) in which lateral convergence generates the strongest winds near the entrance of the gap. Trajectory analysis of the flow in the strongest events, the mountain wave events, confirms the importance of net subsidence in creating high wind speeds. Neglect of vertical motion in applications of Bernoulli's equation to gap flows is shown to lead to unreasonable wind speed predictions whenever the temperature at the gap exit exceeds that at the gap entrance. The distribution of the Bernoulli function on an isentropic surface shows a correspondence between regions of high Bernoulli function and high wind speeds in the gap-exit jet similar to that previously documented for shallow-water flow.

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Dependence of Power Characteristics on Savonius Rotor Segmentation

Energies ◽

10.3390/en14102912 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2912

Author(s):

Krzysztof Doerffer ◽

Janusz Telega ◽

Piotr Doerffer ◽

Paulina Hercel ◽

Andrzej Tomporowski

Keyword(s):

High Wind ◽

Horizontal Axis Wind Turbine ◽

Savonius Rotor ◽

Power Characteristics ◽

Wind Speeds ◽

Single Segment ◽

High Elongation ◽

Low Wind Speeds ◽

Number Of Segments ◽

Rotor Type

Savonius rotors are large and heavy because they use drag force for propulsion. This leads to a larger investment in comparison to horizontal axis wind turbine (HAWT) rotors using lift forces. A simple construction of the Savonius rotor is preferred to reduce the production effort. Therefore, it is proposed here to use single-segment rotors of high elongation. Nevertheless, this rotor type must be compared with a multi-segment rotor to prove that the simplification does not deteriorate the effectiveness. The number of segments affects the aerodynamic performance of the rotor, however, the results shown in the literature are inconsistent. The paper presents a new observation that the relation between the effectiveness of single- and multi-segment rotors depends on the wind velocity. A single-segment rotor becomes significantly more effective than a four-segment rotor at low wind speeds. At high wind speeds, the effectiveness of both rotors becomes similar.

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Traffic Density-Related Black Carbon Distribution: Impact of Wind in a Basin Town

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18126490 ◽

2021 ◽

Vol 18 (12) ◽

pp. 6490

Author(s):

Borut Jereb ◽

Brigita Gajšek ◽

Gregor Šipek ◽

Špela Kovše ◽

Matevz Obrecht

Keyword(s):

Black Carbon ◽

Carbon Concentration ◽

Ground Level ◽

Traffic Density ◽

Carbon Distribution ◽

Wind Speeds ◽

Black Carbon Concentration ◽

Low Wind Speeds ◽

Temperature Inversions ◽

Carbon Concentrations

Black carbon is one of the riskiest particle matter pollutants that is harmful to human health. Although it has been increasingly investigated, factors that depend on black carbon distribution and concentration are still insufficiently researched. Variables, such as traffic density, wind speeds, and ground levels can lead to substantial variations of black carbon concentrations and potential exposure, which is even riskier for people living in less-airy sites. Therefore, this paper “fills the gaps” by studying black carbon distribution variations, concentrations, and oscillations, with special emphasis on traffic density and road segments, at multiple locations, in a small city located in a basin, with frequent temperature inversions and infrequent low wind speeds. As wind speed has a significant impact on black carbon concentration trends, it is critical to present how low wind speeds influence black carbon dispersion in a basin city, and how black carbon is dependent on traffic density. Our results revealed that when the wind reached speeds of 1 ms−1, black carbon concentrations actually increased. In lengthy wind periods, when wind speeds reached 2 or 3 ms−1, black carbon concentrations decreased during rush hour and in the time of severe winter biomass burning. By observing the results, it could be concluded that black carbon persists longer in higher altitudes than near ground level. Black carbon concentration oscillations were also seen as more pronounced on main roads with higher traffic density. The more the traffic decreases and becomes steady, the more black carbon concentrations oscillate.

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Spray deposits from aerial insecticide spray simulant applications to a coniferous plantation in low and high wind speeds

Crop Protection ◽

10.1016/0261-2194(94)90162-7 ◽

1994 ◽

Vol 13 (2) ◽

pp. 121-126 ◽

Cited By ~ 3

Author(s):

Nicholas J. Payne

Keyword(s):

High Wind ◽

Wind Speeds ◽

Coniferous Plantation ◽

Insecticide Spray

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Midlatitude cyclones in convection permitting climate simulations: the added value offered for extreme wind speeds and sting-jets

10.5194/egusphere-egu21-12795 ◽

2021 ◽

Author(s):

Colin Manning ◽

Elizabeth Kendon ◽

Hayley Fowler ◽

Nigel Roberts ◽

Segolene Berthou ◽

...

Keyword(s):

Climate Model ◽

Surface Wind ◽

Added Value ◽

Large Contribution ◽

High Wind ◽

Wind Speeds ◽

Wind Gusts ◽

Climate Simulations ◽

Extreme Wind ◽

Extreme Wind Speeds

<p>Extra-tropical windstorms are one of the costliest natural hazards affecting Europe, and windstorms that develop a phenomenon known as a sting-jet account for some of the most damaging storms. A sting-jet (SJ) is a mesoscale core of high wind speeds that occurs in particular types of cyclones, specifically Shapiro-Keyser (SK) cyclones, and can produce extremely damaging surface wind gusts. High-resolution climate models are required to adequately model SJs and so it is difficult to gauge their contribution to current and future wind risk. In this study, we develop a low-cost methodology to automate the detection of sting jets, using the characteristic warm seclusion of SK cyclones and the slantwise descent of high wind speeds, within pan-European 2.2km convection-permitting climate model (CPM) simulations. Following this, we quantify the contribution of such storms to wind risk in Northern Europe in current and future climate simulations, and secondly assess the added value offered by the CPM compared to a traditional coarse-resolution climate model. This presentation will give an overview of the developed methods and the results of our analysis.</p><p>Comparing with observations, we find that the representation of wind gusts is improved in the CPM compared to ERA-Interim reanalysis data. Storm severity metrics indicate that SK cyclones account for the majority of the most damaging windstorms. The future simulation produces a large increase (>100%) in the number of storms exceeding high thresholds of the storm metric, with a large contribution to this change (40%) coming from windstorms in which a sting-jet is detected. Finally, we see a systematic underestimation in the GCM compared to the CPM in the frequency of extreme wind speeds at 850hPa in the cold sector of cyclones, likely related to better representation of sting-jets and the cold conveyor belt in the CPM. This underestimation is between 20-40% and increases with increasing wind speed above 35m/s. We conclude that the CPM adds value in the representation of severe surface wind gusts, providing more reliable future projections and improved input for impact models.</p>

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Relationship between Sea Surface Drag Coefficient and Wave State

Journal of Marine Science and Engineering ◽

10.3390/jmse9111248 ◽

2021 ◽

Vol 9 (11) ◽

pp. 1248

Author(s):

Jian Shi ◽

Zhihao Feng ◽

Yuan Sun ◽

Xueyan Zhang ◽

Wenjing Zhang ◽

...

Keyword(s):

Drag Coefficient ◽

Momentum Flux ◽

Sea Surface ◽

Sea Spray ◽

Wave Age ◽

High Wind ◽

Surface Drag ◽

Wave State ◽

Wind Speeds ◽

Strong Winds

The sea surface drag coefficient plays an important role in momentum transmission between the atmosphere and the ocean, which is affected by ocean waves. The total air–sea momentum flux consists of effective momentum flux and sea spray momentum flux. Sea spray momentum flux involves sea surface drag, which is largely affected by the ocean wave state. Under strong winds, the sea surface drag coefficient (CD) does not increase linearly with the increasing wind speed, namely, the increase of CD is inhibited by strong winds. In this study, a sea surface drag coefficient is constructed that can be applied to the calculation of the air–sea momentum flux under high wind speed. The sea surface drag coefficient also considers the influence of wave state and sea spray droplets generated by wave breaking. Specially, the wave-dependent sea spray generation function is employed to calculate sea spray momentum flux. This facilitates the analysis not only on the sensitivity of the sea spray momentum flux to wave age, but also on the effect of wave state on the effective CD (CD, eff) under strong winds. Our results indicate that wave age plays an important role in determining CD. When the wave age is >0.4, CD decreases with the wave age. However, when the wave age is ≤0.4, CD increases with the wave age at low and moderate wind speeds but tends to decrease with the wave age at high wind speeds.

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A Review of Parameterizations for Enthalpy and Momentum Fluxes from Sea Spray in Tropical Cyclones

Journal of Physical Oceanography ◽

10.1175/jpo-d-21-0023.1 ◽

2021 ◽

Author(s):

Sydney Sroka ◽

Kerry Emanuel

Keyword(s):

Tropical Cyclones ◽

Critical Role ◽

Sea Spray ◽

High Wind ◽

High Wind Speed ◽

Wind Speeds ◽

Crucial Component ◽

Momentum Fluxes ◽

Interaction Scheme ◽

Speed Regime

AbstractThe intensity of tropical cyclones is sensitive to the air-sea fluxes of enthalpy and momentum. Sea spray plays a critical role in mediating enthalpy and momentum fluxes over the ocean’s surface at high wind speeds, and parameterizing the influence of sea spray is a crucial component of any air-sea interaction scheme used for the high wind regime where sea spray is ubiquitous. Many studies have proposed parameterizations of air-sea flux that incorporate the microphysics of sea spray evaporation and the mechanics of sea spray stress. Unfortunately, there is not yet a consensus on which parameterization best represents air-sea exchange in tropical cyclones, and the different proposed parameterizations can yield substantially different tropical cyclone intensities. This paper seeks to review the developments in parameterizations of the sea spray-mediated enthalpy and momentum fluxes for the high wind speed regime and to synthesize key findings that are common across many investigations.

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