Airflows and turbulent flux measurements in mountainous terrain

Turnipseed, Andrew A.; Anderson, Dean E.; Burns, Sean P.; Blanken, Peter D.; Monson, Russell K.

doi:10.1016/j.agrformet.2004.04.007

Cited by 94 publications

(110 citation statements)

References 40 publications

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“…In the present case, the drainage flow was well mixed, so homogeneity of CO 2 concentration is a reasonable assumption (Fig. For example, wind speeds measured above the canopy are unlikely to represent wind speeds on the adjacent vegetated slope at the same elevation because of frictional drag exerted by the foliage (e.g., Fons 1940, Allen 1968, Landsberg 1971, Shaw 1977, Turnipseed et al 2003. However, wind speeds were not likely to be horizontally homogeneous.…”

Section: Advected Co 2 Flux Estimatesmentioning

confidence: 75%

“…If the land surface is sparsely vegetated, most of the radiative cooling occurs close to the ground, and the flow travels below the canopies of any trees that may be present. In heavily vegetated terrain, the drainage may extend below the canopy, creating regions of high windspeeds above the canopy and near the ground (s-shaped vertical wind profile; e.g., Fons 1940, Allen 1968, Landsberg and James 1971, Shaw 1977, Turnipseed et al 2003. If the slope is heavily vegetated, the radiating surface to the night sky is the top of the canopy rather than the ground, and a drainage flow may occur above the canopy (Komatsu et al 2003).…”

Section: Introductionmentioning

confidence: 99%

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Using Nocturnal Cold Air Drainage Flow to Monitor Ecosystem Processes in Complex Terrain

Pypker

Unsworth

Mix

et al. 2007

Ecological Applications

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This paper presents initial investigations of a new approach to monitor ecosystem processes in complex terrain on large scales. Metabolic processes in mountainous ecosystems are poorly represented in current ecosystem monitoring campaigns because the methods used for monitoring metabolism at the ecosystem scale (e.g., eddy covariance) require flat study sites. Our goal was to investigate the potential for using nocturnal down-valley winds (cold air drainage) for monitoring ecosystem processes in mountainous terrain from two perspectives: measurements of the isotopic composition of ecosystem-respired CO2 (delta13C(ER)) and estimates of fluxes of CO2 transported in the drainage flow. To test if this approach is plausible, we monitored the wind patterns, CO2 concentrations, and the carbon isotopic composition of the air as it exited the base of a young (approximately 40 yr-old) and an old (>450 yr-old) steeply sided Douglas-fir watershed. Nocturnal cold air drainage within these watersheds was strong, deep, and occurred on more than 80% of summer nights. The depth of cold air drainage rapidly increased to tower height or greater when the net radiation at the top of the tower approached zero. The carbon isotope composition of CO2 in the drainage system holds promise as an indicator of variation in basin-scale physiological processes. Although there was little vertical variation in CO2 concentration at any point in time, we found that the range of CO2 concentration over a single evening was sufficient to estimate delta 13C(ER) from Keeling plot analyses. The seasonal variation in delta 13C(ER) followed expected trends: during the summer dry season delta 13C(ER) became less negative (more enriched in 13C), but once rain returned in the fall, delta 13C(ER) decreased. However, we found no correlation between recent weather (e.g., vapor pressure deficit) and delta 13C(ER) either concurrently or with up to a one-week lag. Preliminary estimates suggest that the nocturnal CO2 flux advecting past the 28-m tower is a rather small fraction (<20%) of the watershed-scale respiration. This study demonstrates that monitoring the isotopic composition and CO2 concentration of cold air drainage at the base of a watershed provides a new tool for quantifying ecosystem metabolism in mountainous ecosystems on the basin scale.

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Section: Advected Co 2 Flux Estimatesmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Using Nocturnal Cold Air Drainage Flow to Monitor Ecosystem Processes in Complex Terrain

Pypker

Unsworth

Mix

et al. 2007

Ecological Applications

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“…sonic anemometers, open and closed-path gas analyzers, net radiometers) were located at the site, with intercomparisons presented in Turnipseed et al (2002). Both localscale and meso-scale effects that influence airflow and turbulent flux measurements are described in Turnipseed et al (2003) and Turnipseed et al (2004), respectively, and a detailed investigation of the role of …”

Section: Subalpine Forest Sitementioning

confidence: 99%

A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado

et al. 2009

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Eddy covariance measurements of the surface energy balance and carbon dioxide exchange above high-elevation (3,480 m above sea level) alpine tundra located near Niwot Ridge, Colorado, were compared to simultaneous measurements made over an adjacent subalpine forest over two summers and one winter, from June 9, 2007 to July 3, 2008. The surface energy balance closure at the alpine site averaged 71 and 91%, winter and summer, respectively, due to the high wind speeds, short turbulent flux footprint, and relatively flat ridgetop location of the measurement site. Throughout the year, the alpine site was cooler with higher relative humidity, and had a higher horizontal wind speed, especially in winter, compared to the forest site. Wind direction was persistently downslope at the alpine site (summer and winter, day and night), whereas upslope winds were common at the forest site during summer daytime periods. The latent and sensible heat fluxes were consistently larger in magnitude at the forest site, with the largest differences during summer. The horizontal advective flux of CO 2 at the alpine site averaged 6% of the net ecosystem exchange (NEE) during summer nights (5% during summer daytime), and was small in relation to the high wind speeds, relatively flat site, and weak sources of CO 2 upwind of the site. The magnitudes and diurnal behavior of the alpine NEE calculated using three methods; eddycovariance, friction velocity filter, and with advection and storage calculations, gave similar results. The period of net CO 2 uptake (negative NEE) was 100 days at the alpine site with a net uptake of 16 g C m -2 , compared to 208 days at the forest site with a net uptake of 108 g C m -2 , with initiation of net uptake coinciding with air temperatures reaching ?10°C. Winter respiration loss at the alpine site was 164 g C m -2 over 271 days, compared to 52 g C m -2 over 175 days at the forest site, with the initiation of net loss coinciding with air temperatures reaching -10°C at each site.

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“…The observational study of Turnipseed et al (2004) identifies gravity waves as the main drivers for the exchange of momentum and energy in stable boundary layers. Up to 50% of the total scalar variance can be accounted for by low frequency waves.…”

Section: Momentum Exchangementioning

confidence: 99%

On the Vertical Exchange of Heat, Mass, and Momentum Over Complex, Mountainous Terrain

et al. 2015

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The role of the atmospheric boundary layer (ABL) in the atmosphere-climate system is the exchange of heat, mass, and momentum between "the earth's surface" and the atmosphere. Traditionally, it is understood that turbulent transport is responsible for this exchange and hence the understanding and physical description of the turbulence structure of the boundary layer is key to assess the effectiveness of earth-atmosphere exchange (EAE). This understanding is rooted in the (implicit) assumption of a scale separation or spectral gap between turbulence and mean atmospheric motions, which in turn leads to the assumption of a horizontally homogeneous and flat (HHF) surface as a reference, for which both physical understanding and model parameterizations have successfully been developed over the years. Over mountainous terrain, however, the ABL is generically inhomogeneous due to both thermal (radiative) and dynamic forcing. This inhomogeneity leads to meso-scale and even sub-meso-scale flows such as slope and valley winds or wake effects. It is argued here that these (sub)meso-scale motions can significantly contribute to the vertical structure of the boundary layer and hence vertical exchange of heat and mass between the surface and the atmosphere. If model grid resolution is not high enough the latter will have to be parameterized (in a similar fashion as gravity wave drag (GWD) parameterizations take into account the momentum transport due to gravity waves in large-scale models). In this contribution we summarize the available evidence of the contribution of (sub)meso-scale motions to vertical exchange in mountainous terrain from observational and numerical modeling studies. In particular, a number of recent simulation studies using idealized topography will be summarized and put into perspective-so as to identify possible limitations and areas of necessary future research.

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Airflows and turbulent flux measurements in mountainous terrain

Cited by 94 publications

References 40 publications

Using Nocturnal Cold Air Drainage Flow to Monitor Ecosystem Processes in Complex Terrain

Using Nocturnal Cold Air Drainage Flow to Monitor Ecosystem Processes in Complex Terrain

A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado

On the Vertical Exchange of Heat, Mass, and Momentum Over Complex, Mountainous Terrain

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