Experimental Design of the 1984 ASCOT Field Study

Clements, W.E.; Archuleta, J.A.; Gudiksen, P.H.

doi:10.1175/1520-0450(1989)028<0405:edotaf>2.0.co;2

Cited by 52 publications

(20 citation statements)

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“…A detailed description of the 1984 ASCOT field study in Brush Creek valley, including technical objectives, measurements, and instrumentation, is given by Clements et al (1989). Brush Creek valley ( Figure 1) is a 25 km long canyon located 55 km NNE of Grand Junction in western Colorado.…”

Section: The 1984 Ascot Experimentsmentioning

confidence: 99%

Observed variations of ?? and ?? in the nocturnal drainage flow in a deep valley

Rao

Schaub

1990

Boundary-Layer Meteorol

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The variations of a0 and o+ in the drainage flow in the Brush Creek valley of western Colorado are investigated using data from Doppler acoustic sodars and instrumented towers. The data were obtained on two experimental nights during the 1984 ASCOT field study. There is good agreement between the o variations derived from low-level observations of the sodars and those derived from the towers located throughout the valley. The observed hourly average crO and a, in the nocturnal drainage flow are about 20" to 25" and Y, respectively; these values are much larger than those generally observed over flat terrain during nighttime stable conditions. After sunrise (about 06OOMST), as the valley warms and the flow direction changes to up-valley, these parameters increase sharply to their peak values at about 0800MST and then decrease to their normal daytime values after about two hours.In the drainage flow, the hourly average a, varies inversely with wind speed according to the relation a&i = 0.7 rns-i. The vertical standard deviation is much less enhanced by complex terrain than the horizontal standard deviation. The observed c+ values are predicted fairly well by the local similarity theory.

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Section: The 1984 Ascot Experimentsmentioning

confidence: 99%

Observed variations of ?? and ?? in the nocturnal drainage flow in a deep valley

Rao

Schaub

1990

Boundary-Layer Meteorol

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“…While these research programmes addressed a broad range of scientific questions, a number of other campaigns targeted specific phenomena, generally in mountain areas with relatively limited geographical extent (ASCOT [26], BLLAST [27], COLPEX [28], COPS [29], CUPIDO [30], DOMEX [31], MATERHORN [32], METCRAX [33], METCRAX II [34], PAP [35], PCAPS [36], Pic 2005 [37], TRACT [38], T-REX [39], VERTIKATOR [40], VOTALP [41], and VTMX [42]). Although they did not focus primarily on exchange in the ABL over mountains, all of these experimental efforts indirectly led to significant progress in the understanding of the relevant processes.…”

Section: Introductionmentioning

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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“…An understanding of the flow structure in mountainous terrain is, however, not only important to weather and climate aspects, but also to other fields such as pollutant transport (e.g. Clements et al 1989) and atmospheric chemistry in Alpine valleys (e.g. Furger et al 2000).…”

Section: Introductionmentioning

confidence: 99%

Flow structure and turbulence characteristics of the daytime atmosphere in a steep and narrow Alpine valley

Weigel

Rotach

2004

Quart J Royal Meteoro Soc

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SUMMARYAircraft measurements, radio soundings and sonic data-obtained during the MAP-Riviera field campaign in autumn 1999 in southern Switzerland-are used to investigate the flow structure, temperature profiles and turbulence characteristics of the atmosphere in a steep and narrow Alpine valley under convective conditions. On all predominantly sunny days of the intensive observation periods, a pronounced valley-wind system develops. In the southern half of the valley, the daily up-valley winds have a jet-like structure and are shifted towards the eastern slope. These up-valley winds advect potentially colder air, a process which appears to be balanced by vertical warm air advection from above. The profiles of potential temperature show that, with the onset of up-valley winds, the mixed layer consistently stops growing or-on days with very strong up-valley winds-even stabilizes almost throughout the entire valley atmosphere. This is probably due to a pronounced secondary circulation in the southern part of the valley, which induces advection of warm air from above. The secondary circulation appears to be a consequence of sharp curvature in the along-valley topography.Turbulence variables are calculated from flight legs in the along-valley direction. Turbulent kinetic energy (TKE) scales surprisingly well (i) if a TKE criterion (TKE > 0.5 m 2 s −2 ) is employed as a definition of the boundary layer height and (ii) if the 'surface fluxes'-which exhibit a substantial spatial variability-from the slope sites are used rather than those from directly beneath the profile considered. Significant site-to-site differences in incoming solar radiation seem to be the reason for this characteristic behaviour. Profiles of momentum flux-scaled with a surface friction velocity-reveal more scatter than the TKE profiles, but still show a consistent behaviour. A surprisingly strong shear in the cross-valley direction can be observed and is probably a result of the secondary circulation.

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Experimental Design of the 1984 ASCOT Field Study

Cited by 52 publications

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Observed variations of ?? and ?? in the nocturnal drainage flow in a deep valley

Observed variations of ?? and ?? in the nocturnal drainage flow in a deep valley

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

Flow structure and turbulence characteristics of the daytime atmosphere in a steep and narrow Alpine valley

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