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William E. Clements
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William E. Clements and Carmen J. Nappo

Abstract

Observations of a drainage flow event on a high-altitude simple slope were made for a few hours during a five-day field study that was otherwise characterized by high and gusty winds blowing across the face of the slope believed due to the presence of a nocturnal jet. A simple slope in the Jemez Mountains of north-central New Mexico was instrumented with meteorological surface stations and 10 m masts. Data collected during the drainage flow event indicate a depth ranging from greater than 10 m at the bottom of the slope to near zero at the top. At the bottom of the slope, the wind speed varied from 2.5 m s−1 at 1.5 m above ground to 0.5 m s−1 at a height of 10 m.

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William M. Porch, William E. Clements, and Richard L. Coulter

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This paper describes a regular oscillation observed in nighttime drainage airflow in a valley under relatively light upper-level wind conditions. The period of these oscillations is about 20 minutes with at least one harmonic at about 10 minutes. A strong coherence between tributary flow and main valley fluctuations was observed, with the phase of the tributary flow leading the valley oscillation; this indicates the importance of tributaries as major contributors to the dynamics of cold air flow in valleys.

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William E. Clements, John A. Archuleta, and Donald E. Hoard

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Wind and temperature data collected by an instrumented tethered balloon and a Doppler lidar in a deep valley are used to investigate the mean properties of the nocturnal drainage flow down the valley on four nights when the wind at ridgetop had an up-valley component. We examine the vertical structure of temperature and the vertical and horizontal structure of the drainage wind. An empirical description of the wind field is derived and used to estimate the mass flux resulting from the drainage flow. Mean properties of the flow are presented and relationships among some of the parameters are examined.

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William E. Clements, John A. Archuleta, and Paul H. Gudiksen

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During September and October of 1984 the Department of Energy's Atmospheric Studies in Complex Terrain program conducted an intensive field study in the Brush Creek Valley of western Colorado. The overall objective of the study was to enhance the understanding of pollutant transport and diffusion associated with valley flows. Data collections were designed to investigate nocturnal and morning transition wind, turbulence, and temperature fields in the valley, in its tributaries, and on its side-slopes, and how these are affected by the free stream conditions above the valley. The release and sampling of atmospheric tracers were used to study transport and diffusion. The experimental design of this study is presented.

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Elmar R. Reiter, John D. Sheaffer, James E. Bossert, Richard C. Fleming, William E. Clements, J. T. Lee, Sumner Barr, John A. Archuleta, and Donald E. Hoard

During the late summer of 1985 a field experiment was conducted to investigate mountaintop winds over a broad area of the Rocky Mountains extending from south central Wyoming through northern New Mexico. The principal motivation for this experiment was to further investigate an unexpectedly strong and potentially important wind cycle observed at mountaintop in north central Colorado during August 1984. These winds frequently exhibited nocturnal maxima of 20 to 30 m · s−1 from southeasterly directions and often persisted for eight to ten hours. It appears that these winds originate as outflow from intense mesoscale convective systems that form daily over highland areas along the Continental Divide. However, details of the spatial extent and variability of these winds could not be determined from “routine” regional weather data that are mostly collected in valleys. Although synoptic conditions during much of the 1985 experiment period did not favor diurnally recurring convection over the study area, sufficient data were obtained to verify the regional-scale organization of strong convective outflow at mountaintop elevations. In addition, the usefulness and feasibility of a mountain-peak weather-data network for routine synoptic analysis is demonstrated.

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Jielun Sun, Steven P. Oncley, Sean P. Burns, Britton B. Stephens, Donald H. Lenschow, Teresa Campos, Russell K. Monson, David S. Schimel, William J. Sacks, Stephan F. J. De Wekker, Chun-Ta Lai, Brian Lamb, Dennis Ojima, Patrick Z. Ellsworth, Leonel S. L. Sternberg, Sharon Zhong, Craig Clements, David J. P. Moore, Dean E. Anderson, Andrew S. Watt, Jia Hu, Mark Tschudi, Steven Aulenbach, Eugene Allwine, and Teresa Coons

A significant fraction of Earth consists of mountainous terrain. However, the question of how to monitor the surface–atmosphere carbon exchange over complex terrain has not been fully explored. This article reports on studies by a team of investigators from U.S. universities and research institutes who carried out a multiscale and multidisciplinary field and modeling investigation of the CO2 exchange between ecosystems and the atmosphere and of CO2 transport over complex mountainous terrain in the Rocky Mountain region of Colorado. The goals of the field campaign, which included ground and airborne in situ and remote-sensing measurements, were to characterize unique features of the local CO2 exchange and to find effective methods to measure regional ecosystem–atmosphere CO2 exchange over complex terrain. The modeling effort included atmospheric and ecological numerical modeling and data assimilation to investigate regional CO2 transport and biological processes involved in ecosystem–atmosphere carbon exchange. In this report, we document our approaches, demonstrate some preliminary results, and discuss principal patterns and conclusions concerning ecosystem–atmosphere carbon exchange over complex terrain and its relation to past studies that have considered these processes over much simpler terrain.

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