Meteorological Events Affecting Cold-Air Pools in a Small Basin

Dorninger, Manfred; Whiteman, C. David; Bica, Benedikt; Eisenbach, Stefan; Pospichal, Bernhard; Steinacker, Reinhold

doi:10.1175/2011jamc2681.1

Cited by 48 publications

(53 citation statements)

References 25 publications

(28 reference statements)

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“…The time-scale of nocturnal cooling is typically shorter in basins and valleys than it is over flat terrain [181]. The formation of cold air pools is favoured by certain geometric properties of the orography (e.g., the sky-view factor and altitude), but their intensity and persistence depend on a few meteorological factors, mostly determined at the synoptic scale (the presence of a cold and dry air mass, weak winds, and a cloudless sky) [182,183].…”

Section: The Stable Boundary Layer At the Valley Floormentioning

confidence: 99%

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

et al. 2018

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Abstract:The exchange of heat, momentum, and mass in the atmosphere over mountainous terrain is controlled by synoptic-scale dynamics, thermally driven mesoscale circulations, and turbulence. This article reviews the key challenges relevant to the understanding of exchange processes in the mountain boundary layer and outlines possible research priorities for the future. The review describes the limitations of the experimental study of turbulent exchange over complex terrain, the impact of slope and valley breezes on the structure of the convective boundary layer, and the role of intermittent mixing and wave-turbulence interaction in the stable boundary layer. The interplay between exchange processes at different spatial scales is discussed in depth, emphasizing the role of elevated and ground-based stable layers in controlling multi-scale interactions in the atmosphere over and near mountains. Implications of the current understanding of exchange processes over mountains towards the improvement of numerical weather prediction and climate models are discussed, considering in particular the representation of surface boundary conditions, the parameterization of sub-grid-scale exchange, and the development of stochastic perturbation schemes.

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Section: The Stable Boundary Layer At the Valley Floormentioning

confidence: 99%

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

et al. 2018

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“…The nature of CAPs depends on the vertical and horizontal scales associated with the terrain. CAPs in small, narrow valleys typically have a fairly simple morphology (Jemmett-Smith, 2014;Sheridan et al, 2014;Vosper et al, 2014), and tend to be diurnal (Gustavsson et al, 1998;Clements et al, 2003;Whiteman et al, 2004;Steinacker et al, 2007;Vosper and Brown, 2008;Whiteman et al, 2008;Bodine et al, 2009;Dorninger et al, 2011;Price et al, 2011;Mahrt et al, 2014;Sheridan et al, 2014). Meanwhile, in broader valleys, CAPs can be more complex in morphology and evolution, with disturbances to the CAP potentially only affecting a part of its area.…”

Section: Introductionmentioning

confidence: 99%

Synoptic‐flow interaction with valley cold‐air pools and effects on cold‐air pool persistence: Influence of valley size and atmospheric stability

Sheridan

2019

Quart J Royal Meteoro Soc

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Idealized two‐dimensional simulations have been used to examine the dependence of valley cold‐air pool (CAP) behaviour, morphology and duration (persistence) on terrain scale. The simulations use terrain of constant aspect ratio but ranging from modest to Alpine scale, under midlatitude winter conditions with a finite background flow and incorporating a diurnal cycle. CAPs in smaller valleys are found to be more morphologically constrained, whereas larger valleys provide scope for more complex flow dynamics and more dramatic interplay of the external flow with the valley, including gravity wave breaking. Simulations of a valley within a plateau show that, as valley depth exceeds the depth‐scale of the nocturnal stable boundary layer, the CAP becomes increasingly confined and sheltered from the background flow (reduced mixing), becoming harder to remove by processes related to daytime insolation, and it can eventually become persistent (never removed). Both the surrounding terrain and gravity wave dynamics are found to play a part in the enhancement of sheltering. Therefore background atmospheric stability and wind are also crucial, summarized in a non‐dimensional valley depth parameter which largely determines CAP duration. More stable conditions, representative of (for instance) large‐scale subsidence or warm advection aloft, result in longer durations and a greater likelihood of persistence. Stronger nocturnal radiative cooling results in stronger CAPs, which are harder again to remove. Several mechanisms appear to act in concert to give rise to these behaviours and the dependence on non‐dimensional valley depth. Replacing the valley‐in‐plateau with a double hill enhances wave breaking, which complicates the relationship to non‐dimensional valley depth, reducing CAP duration significantly when subsidence or warm advection‐like effects are absent.

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“…Traditionally, cold-air flow is analyzed using measurements of air temperature, wind speed and wind direction at different heights above the ground (e.g., Schwab 2000;Dietrich and Böhner 2008), and at various locations in transects along a slope Dorninger et al 2011). Cold-air flow can also be visualized using fog machines, which emit dense suspensions of small liquid particles highlighting flow dynamics, and analyzed in tracer experiments (e.g., Allwine et al 1992;Pypker et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Capturing Cold-Air Flow Using Thermal Imaging

Grudzielanek

Čermák

2015

Boundary-Layer Meteorol

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We present a thermal imaging field design for climatological studies with an application to microscale cold-air flow analysis. Measurements of microclimatic processes are often limited by a lack of spatial coherence and consequently incomplete information on spatial and temporal patterns in the airflow. We introduce and evaluate an approach for investigating cold-air flow using an infrared camera pointed at a custom-built projection screen. A statistical analysis of a cold-air-flow case study is presented that explores the potential and limitations of the proposed technique. Results indicate good compatibility with traditional methods, while spatial coherence in measurements is achieved. A few examples of additional information obtained from the thermal camera analysis are presented, including analyses of cold-air-flow characteristics.

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Meteorological Events Affecting Cold-Air Pools in a Small Basin

Cited by 48 publications

References 25 publications

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

Synoptic‐flow interaction with valley cold‐air pools and effects on cold‐air pool persistence: Influence of valley size and atmospheric stability

Capturing Cold-Air Flow Using Thermal Imaging

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