Flow Regimes and Transient Dynamics of Two-Dimensional Stratified Flow over an Isolated Mountain Ridge

Lin, Yuh-Lang; Wang, Ting-An

doi:10.1175/1520-0469(1996)053<0139:fratdo>2.0.co;2

Cited by 56 publications

(53 citation statements)

References 0 publications

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“…Pierrehumbert and Wyman, 1985), where N is the BruntÁVa¨isa¨la¨frequency, describing the buoyancy on a vertically displaced air parcel, h is the mountain height and U is the flow speed of the airmass impinging on the mountain (e.g. Peng et al, 1995;Tru¨b and Davies, 1995;Lin and Wang, 1996;Ó lafsson and Bougeault, 1996). High values of hˆfacilitate for blocked flow leading to more of the flow going around than over the mountain.…”

Section: Introductionsupporting

confidence: 69%

Simulations of the Bergen orographic wind shelter

Jonassen

Ólafsson

Valved

et al. 2013

Tellus A: Dynamic Meteorology and Oceanography

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A B S T R A C T Even though the coast of western Norway is very windy, the centre of Bergen is rather calm. To gain further understanding of this wind shelter, we study the flow in the complex topography of Bergen during two southwesterly windstorms using surface observations and high-resolution numerical simulations. The results reveal large spatial variability in the local wind field. In some areas, there are periods of sustained winds of more than 25 m s At Florida, situated close to the city centre, both a wake effect of Løvstakken and a blocking effect of Fløyen are evident, but the latter is more prominent. The total impact of both mountains on the winds in the city is close to the sum of each of them. A spillover effect of Løvstakken acts to substantially increase the local precipitation in the centre of Bergen. The spillover effect is presumably less pronounced for cases with weaker winds.

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Section: Introductionsupporting

confidence: 69%

Simulations of the Bergen orographic wind shelter

Jonassen

Ólafsson

Valved

et al. 2013

Tellus A: Dynamic Meteorology and Oceanography

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“…Some early theoretical studies (Long 1953;Miles and Huppert 1968) elucidated the nonlinear mechanisms for an early stage of the wave breaking processes. Understanding of these mechanisms has been significantly enriched through numerical experiments (Laprise and Peltier 1989;Lin and Wang 1996;Jiang et al 2004;McHugh and Sharman 2013). For a highly simplified case of uniform stratification and wind profile, a Mountain Froude number (cf.…”

Section: Accelerated Deposition Via Breaking Lee Wavesmentioning

confidence: 99%

“…Leewave breaking occurs when Fr is about equal to or smaller than unity (e.g. Lin and Wang 1996). The condition of Fr∼1 is not an unusual one; for example, if we take a climatological lapse rate of 0.006 K m −1 for the troposphere (NOAA 1976;Wallace and Hobbs 2006), which gives N≈0.0117 s −1 , a wind speed of U=12 m s −1 , and a mountain with h=1,000 m, the Mountain Froude number is Fr≈1.02.…”

Section: Accelerated Deposition Via Breaking Lee Wavesmentioning

confidence: 99%

An example of enhanced tephra deposition driven by topographically induced atmospheric turbulence

et al. 2015

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Spatial variations in the thickness and grain-size characteristics of tephra fall deposits imply that tephra depositional processes cannot be fully captured by models of single-particle sedimentation from the base of the eruption plume. Here, we document a secondary thickness maximum in a ∼9.75 ka tephra fall deposit from Chaitén volcano, Chile (Cha1 eruption). This secondary thickness maximum is notably coarser-grained than documented historical examples, being dominated by medium-grained ash, and an origin via particle aggregation is therefore unlikely. In the region of secondary thickening, we propose that high levels of atmospheric turbulence accelerated particles held within the mid-to lower-troposphere (0 to ∼6 km) towards the ground surface. We suggest that this enhancement in vertical atmospheric mixing was driven by the breaking of lee waves, generated by winds passing over elevated topography beneath the eruption plume. Lower atmospheric circulation patterns may exert a significant control on the dispersal and deposition of tephra from eruption plumes across all spatial scales, particularly in areas of complex topography.

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“…In the literature, various flow regimes based on this parameter are described (e.g. Peng et al, 1995;Triib and Davies, 1995;Lin and Wang, 1996;Ó lafsson and Bougeault, 1996). Smith (1989) outlined three main flow regimes over simple 3-D mountains: Low values of Nh/U enable the flow to pass over the mountain without any stagnation, and typically gentle gravity waves are formed.…”

Section: Theorymentioning

confidence: 99%

Multi-scale variability of winds in the complex topography of southwestern Norway

Jonassen¹,

Ólafsson

Reuder³

et al. 2012

Tellus A: Dynamic Meteorology and Oceanography

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A B S T R A C T Multi-scale variability of winds in the complex terrain of southwestern Norway is investigated using up to 20 yr of observations from nine automatic weather stations and reanalysis data. Significant differences between the large-and local-scale winds are found. These differences are mainly governed by the large-scale topography of Southern Norway. Winds from the southeast and statically stable flow from the northwest are found to be significantly reduced at the ground level due to large-scale wake and blocking effects. Southwesterly and northeasterly winds are orographically enhanced. At a local scale, there are differences in the wind speed distributions between the surface stations, both in space and time. These differences can to a large extent be quantified in terms of the Weibull distribution function and associated with the respective geographical locations as discretised in four characteristic surface categories: offshore, inland, coast and mountain. The inland category is found to be associated with relatively low but variable wind speeds, whereas the coastal and offshore locations are dominated by more steady and stronger winds. The mountain wind speed distribution is fundamentally different from the others; it shares the variability with the inland locations but the higher average wind speed with the other categories.

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Flow Regimes and Transient Dynamics of Two-Dimensional Stratified Flow over an Isolated Mountain Ridge

Cited by 56 publications

References 0 publications

Simulations of the Bergen orographic wind shelter

Simulations of the Bergen orographic wind shelter

An example of enhanced tephra deposition driven by topographically induced atmospheric turbulence

Multi-scale variability of winds in the complex topography of southwestern Norway

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