An Observational History of Small‐Scale Katabatic Winds in Mid‐Latitudes

Poulos, Greg; Zhong, Shiyuan

doi:10.1111/j.1749-8198.2008.00166.x

Cited by 37 publications

(27 citation statements)

References 92 publications

(179 reference statements)

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“…This type of flow is often observed in regions of complex orography and substantially affects the weather and climate in these regions (e.g., Poulos and Zhong, 2008). The topic of katabatic and anabatic wind is being actively explored and the work on its understanding includes the application of numerical models (direct numerical simulations (DNS): (e.g., Shapiro and Fedorovich, 2008); large eddy simulations (LES): e.g., Skyllingstad, 2003;Smith and Porté-Agel, 2013); mesoscale models: (e.g., Smith and Skyllingstad, 2005;Zammett and Fowler, 2007); and analytical models (e.g., Prandtl, 1942;Defant, 1949;Grisogono and Oerlemans, 2001;Zardi and Serafin, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Although the latter authors state that turbulent anabatic flows differ more, in a mean qualitative sense, from its Prandtl model version for katabatic flows, they still show and claim the overall applicability of the Prandtl model (at least qualitatively) to both flow types. In parallel to current theoretical and numerical modeling efforts, large observational campaigns and programs over complex orography should be of a high priority in order to better understand the nature of thermally driven slope flows (e.g., Poulos and Zhong, 2008;Fernando et al, 2015;Grachev et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

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Energetics of Slope Flows: Linear and Weakly Nonlinear Solutions of the Extended Prandtl Model

et al. 2016

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The Prandtl model succinctly combines the 1D stationary boundary-layer dynamics and thermodynamics of simple anabatic and katabatic flows over uniformly inclined surfaces. It assumes a balance between the along-the-slope buoyancy component and adiabatic warming/cooling, and the turbulent mixing of momentum and heat. In this study, energetics of the Prandtl model is addressed in terms of the total energy (TE) concept. Furthermore, since the authors recently developed a weakly nonlinear version of the Prandtl model, the TE approach is also exercised on this extended model version, which includes an additional nonlinear term in the thermodynamic equation. Hence, interplay among diffusion, dissipation, and temperature-wind interaction of the mean slope flow is further explored. The TE of the nonlinear Prandtl model is assessed in an ensemble of solutions where the Prandtl number, the slope angle and the nonlinearity parameter are perturbed. It is shown that nonlinear effects have the lowest impact on variability in the ensemble of solutions of the weakly nonlinear Prandtl model when compared to the other two governing parameters. The general behavior of the nonlinear solution is similar to the linear solution, except that the maximum of the along-the-slope wind speed in the nonlinear solution reduces for larger slopes. Also, the dominance of PE near the sloped surface, and the elevated maximum of KE in the linear and nonlinear energetics of the extended Prandtl model are found in the PASTEX-94 measurements. The corresponding level where KE>PE most likely marks the bottom of the sublayer subject to shear-driven instabilities. Finally, possible limitations of the weakly nonlinear solutions of the extended Prandtl model are raised. In linear solutions, the local storage of TE term is zero, reflecting the stationarity of solutions by definition. However, in nonlinear solutions, the diffusion, dissipation and interaction terms (where the height of the maximum interaction is proportional to the height of the low-level jet by the factor ≈4/9) do not balance and the local storage of TE attains nonzero values. In order to examine the issue of non-stationarity, the inclusion of velocity-pressure covariance in the momentum equation is suggested for future development of the extended Prandtl model.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Energetics of Slope Flows: Linear and Weakly Nonlinear Solutions of the Extended Prandtl Model

et al. 2016

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“…Thermally driven exit jets, the focus of this paper, occur most readily under the relatively quiescent large-scale weather conditions that produce diurnal mountain circulations. Despite anecdotal descriptions of the regular occurrence of these flows in many mountain regions, relatively little scientific attention has been focused on thermally driven canyon exit jets (hereinafter referred to simply as canyon or valley-exit jets), even though the scientific literature on thermally driven winds inside mountain valleys is quite extensive [see recent reviews by Zardi and Whiteman (2012) and Poulos and Zhong (2008)]. …”

Section: Introductionmentioning

confidence: 99%

Observations of Thermally Driven Wind Jets at the Exit of Weber Canyon, Utah

Chrust

Whiteman

Hoch

2013

Journal of Applied Meteorology and Climatology

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Thermally driven valley-exit jets were investigated at Utah's Weber Canyon, a main tributary of the Great Salt Lake basin. An intensive measurement campaign during July-September 2010 supplemented longerterm measurements to characterize the wind and temperature structure in the vicinity of the canyon exit. Exit jets at Weber Canyon are most frequent in late summer or early fall. Strong low-level-wind jets formed at the canyon exit on 75 of 90 nights (83%) during the measurement campaign, with the best-developed winds forming during synoptically undisturbed, clear-sky periods. Winds inside the canyon consisted of a weak down-valley flow layer that occupied most of the 1000-m depth of the canyon. The flow was observed to descend, thin, and accelerate at the valley exit, producing winds that were typically 2.5 times as strong but much more shallow than those inside the canyon. Maximum nighttime jet-axis wind speeds of 15-20 m s 21 are typically found about 80-120 m above the ground at the canyon exit on clear undisturbed nights in the late summer and fall. The jets form 1-3 h after sunset, approach a near-steady state during the late night, and continue until 5-6 h after sunrise, although slowly losing speed after sunrise. The jet is a local modification at the canyon exit of the thermally driven down-valley flow. Its continuation after sunrise is thought to be caused by the nighttime buildup and persistence of a cold-air pool in the Morgan Basin at the east end of the canyon. The potential for utilizing the exit jet for wind power generation is discussed.

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“…The conditions governing the katabatic flow can be divided into internal and external influences (Poulos and Zhong, ). Internal influences include the interaction between the predominant katabatic flow and tributaries (Start et al ; Erasmus, ) and sporadic breakdowns or oscillations within the katabatic flow and surrounding stable boundary layer (Buettner and Thyer, ; Manins and Sawford, ; Nappo, ).…”

Section: Introductionmentioning

confidence: 99%

The evolution and sensitivity of katabatic flow dynamics to external influences through the evening transition

Jensen

Nadeau

Hoch

et al. 2016

Quart J Royal Meteoro Soc

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Data collected over an arid shallow slope (2-4 • ) during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program are used to study the katabatic structure and onset of katabatic flow through the evening transition. An unprecedented suite of instrumentation, including a transect of five turbulence towers with 29 sonic anemometers, is used for the investigation. Fifteen transition periods with well-defined katabatic flow and relatively little synoptic forcing are used in the study. The katabatic onset, jet velocity and jet height all show a large degree of interdiurnal and intersite variance. The slope-aligned budgets of momentum and potential temperature are used to define time-scales that describe the evolution of the katabatic flow. Composite wind velocity time series are used to show that ≈30 min elapses from the time when the katabatic flow initializes at 0.5 m to the point of initialization at 20 m. A simple katabatic model utilizing surface energy-budget modelling is developed and used to model the interdiurnal katabatic variance. Finally, uni-and multi-variate statistical analyses are used to diagnose the influence of specific external variables. Valley wind speed, turbulence structure, soil moisture, and shadow front speed are all found to influence the katabatic dynamics to varying degrees.

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An Observational History of Small‐Scale Katabatic Winds in Mid‐Latitudes

Cited by 37 publications

References 92 publications

Energetics of Slope Flows: Linear and Weakly Nonlinear Solutions of the Extended Prandtl Model

Energetics of Slope Flows: Linear and Weakly Nonlinear Solutions of the Extended Prandtl Model

Observations of Thermally Driven Wind Jets at the Exit of Weber Canyon, Utah

The evolution and sensitivity of katabatic flow dynamics to external influences through the evening transition

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