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Title: Spatially averaging cross-wind sensors and numerical-model results for nocturnal drainage winds in complex terrain

Abstract

Recent studies in The Geysers region of Northern California have concentrated on drainage wind effects on tracer transport and diffusion in complex terrain, as part of the Atmospheric Studies in Complex Terrain (ASCOT) project. These studies combined tracer measurements, conventional tower and remote sensing meteorological measurements, and numerical wind field transport and diffusion models. One part of the meteorological measurement support used eight optical cross-path wind sensors across the principle air drainage valleys. These sensors had varying optical path lengths within the drainage layer of approx. 300 m to 3 km. Results of this study indicate that the combination of spatially averaged cross-path optical wind sensor and conventional tower mounted cup-vane anemometer data into a numerical plume transport and diffusion model for complex terrain has provided useful results. The most important of these results is an independent measure of wind data on a spatial scale compatible with necessarily large grid scales in numerical wind field models with topography. This allows assessment of terrain associated exposure problems for tower anemometers in complex terrain. The optical cross wind data can be used to compare necessary averaging times, and spatial distribution of point sensors and provide verification data to improve the logistics ofmore » instrument placement in combination with numerical models.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (USA)
OSTI Identifier:
6567019
Report Number(s):
UCRL-87797; CONF-830307-2
ON: DE82021220
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: 6. American Meteorological Society symposium on turbulence and diffusion, Boston, MA, USA, 22 Mar 1983; Other Information: Portions are illegible in microfiche products
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; AIR POLLUTION; ENVIRONMENTAL TRANSPORT; COMPLEX TERRAIN; METEOROLOGY; WIND; VELOCITY; ANEMOMETERS; COMPARATIVE EVALUATIONS; DIFFUSION; DRAINAGE; MATHEMATICAL MODELS; NOCTURNAL VARIATIONS; SPATIAL DISTRIBUTION; TRACER TECHNIQUES; DISTRIBUTION; ISOTOPE APPLICATIONS; MASS TRANSFER; MEASURING INSTRUMENTS; POLLUTION; VARIATIONS; 500100* - Environment, Atmospheric- Basic Studies- (-1989); 500200 - Environment, Atmospheric- Chemicals Monitoring & Transport- (-1989)

Citation Formats

Porch, W.M., and Lange, R. Spatially averaging cross-wind sensors and numerical-model results for nocturnal drainage winds in complex terrain. United States: N. p., 1982. Web.
Porch, W.M., & Lange, R. Spatially averaging cross-wind sensors and numerical-model results for nocturnal drainage winds in complex terrain. United States.
Porch, W.M., and Lange, R. 1982. "Spatially averaging cross-wind sensors and numerical-model results for nocturnal drainage winds in complex terrain". United States. doi:.
@article{osti_6567019,
title = {Spatially averaging cross-wind sensors and numerical-model results for nocturnal drainage winds in complex terrain},
author = {Porch, W.M. and Lange, R.},
abstractNote = {Recent studies in The Geysers region of Northern California have concentrated on drainage wind effects on tracer transport and diffusion in complex terrain, as part of the Atmospheric Studies in Complex Terrain (ASCOT) project. These studies combined tracer measurements, conventional tower and remote sensing meteorological measurements, and numerical wind field transport and diffusion models. One part of the meteorological measurement support used eight optical cross-path wind sensors across the principle air drainage valleys. These sensors had varying optical path lengths within the drainage layer of approx. 300 m to 3 km. Results of this study indicate that the combination of spatially averaged cross-path optical wind sensor and conventional tower mounted cup-vane anemometer data into a numerical plume transport and diffusion model for complex terrain has provided useful results. The most important of these results is an independent measure of wind data on a spatial scale compatible with necessarily large grid scales in numerical wind field models with topography. This allows assessment of terrain associated exposure problems for tower anemometers in complex terrain. The optical cross wind data can be used to compare necessary averaging times, and spatial distribution of point sensors and provide verification data to improve the logistics of instrument placement in combination with numerical models.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1982,
month =
}

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  • The application of spatial averaging remote sensing of meteorological measurements in complex terrain wind field determination is described. These measurements prove useful in determining the spatial and temporal representativity of wind fields determined from tower mounted conventional anemometers in complex terrain, as well as providing useful direct input to numerical pollution transport models. These models are limited to grid sizes of hundreds of meters in complex terrain to include the tropographic effects over distances of many miles. Spatially averaged winds are ideal input under these circumstances and have been shown to improve the model results. 11 references, 6 figures, 1more » table.« less
  • Flow visualization studies of the interaction of tributary airflow with main valley airflow under nocturnal drainage conditions were conducted in Brush Creek Valley, Colorado, in June and September-October 1984. The field experiment was designed to document the transport and diffusion of potential local emissions, simulated in this case by release of three chemically inert perfluorocarbons, in a region of highly variable topography. Flow visualization experiments were conducted using smoke releases and nighttime photography. Results indicate that drainage flow entering Pack Canyon from above the ridge is entrained only marginally, if at all, into the near-surface drainage layer within the lowermore » portions of Pack Canyon. This may be due partly to the turbulence and entrainment created at the head of the canyon by the two merging gulches. This mixing may give the descending drainage air at that point enough buoyance to remain aloft and be carried over the south ridge of Pack Canyon by the impetus from the northernmost gully forming Pack Canyon. The split flow evidenced by the smoke plumes shows that the external wind field above the Brush Creek Canyon sidewalls sometimes descends below the ridge to disrupt flows within the canyon. Data from the minisodar and tethersonde show that there is a weak shallow near-surface downslope flow within the canyon that is sometimes disrupted in a periodic fashion by fluctuations in the layers directly above it and in Brush Creek Canyon itself, as indicated by the decrease in periodicity after the Brush Creek Canyon drainage flow has weakened or reversed.« less
  • The complex conditions posed by very localized winds and turbulence, rugged topography, variable surface roughness, strong vertical motions and gravity flow require a three-dimensional modeling approach to realistically simulate the dispersal of hydrogen sulfide injected into the atmosphere at the Geysers geothermal area. In this study the three-dimensional particle-in-cell numerical diffusion model ADPIC (Lange, 1973 and 1978) was used to simulate the transport and diffusion of two simultaneous, distinguishable fluorescent tracer releases into the nighttime drainage flow regimes of the Putah and Anderson Creeks in the Anderson Springs Valley during the night of July 24, 1979.
  • An approximate formulation of the problem of nocturnal drainage flow has been incorporated into a computer code. This formulation, representing a generalization of the shallow fluid approximation, is applicable to complex terrain and accounts for many of the salient physical effects exhibited by drainage flow. These include the dynamics of the katabatic flow, radiation cooling, surface drag, entrainment of the overlying layer, the Coriolis force and interaction with the synoptic flow. Example calculations have been performed in one and two horizontal dimensions. These calculations exhibit a number of interesting qualitative flow features which have been observed, such as thinning ofmore » the layer over ridges and pooling in valleys. We also find that hydraulic jumps are present in the flow. The calculation shows qualitatively correct behavior at modest computational cost. Several processes which are represented parametrically can probably be tuned by comparison with data. Also, by virtue of the low cost of calculations, the model can be applied widely with a resulting gain in experience in how to best use the output. Having cited these advantages, however, it must be recognized that the model is markedly limited by its lack of vertical resolution. The more detailed description afforded by the truly three-dimensional model is necessary for a more complete understanding of this vertical structure.« less
  • The interaction of meteorological data taken at points in a region with numerical models can be done smoothly in gently varying terrain. However, it is fraught with difficulties in complex terrain. Computer memory size limits the resolution of the topography and a point measurement becomes representative of smaller scales as the topography becomes more complex. This paper describes how remotely sensed spatially averaged winds from optical anemometers can be used to help the interaction of wind measurements made at points within a region and numerical regional wind field models. In this paper, emphasis will be placed on model validation bothmore » as wind field estimates for applications such as wind energy prospecting, and as input to pollutant dispersion models.« less