HR: 0800h
AN: B41D-0230    [Abstracts]
TI: Can Nocturnal Cold Air Drainage be Used to Monitor Ecosystem Function?
AU: * Pypker, T G
EM: pypkert@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Science 104 Ocean Admin Building, Corvallis, OR 97331 United States
AU: Unsworth, M H
EM: unsworthm@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Science 104 Ocean Admin Building, Corvallis, OR 97331 United States
AU: Sulzman, E W
EM: Elizabeth.sulzman@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science ALS Building, Corvallis, OR 97331 United States
AU: Lamb, B
EM: blamb@wsu.edu
AF: Washington State University, Department of Civil and Environmental Engineering, Pullman, WA 99164 United States
AU: Allwine, G
EM: allwineg@wsu.edu
AF: Washington State University, Department of Civil and Environmental Engineering, Pullman, WA 99164 United States
AU: Mix, A C
EM: amix@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Science 104 Ocean Admin Building, Corvallis, OR 97331 United States
AU: Bond, B J
EM: barbara.bond@oregonstate.edu
AF: Oregon State University, Department of Forest Science Richardson Hall, Corvallis, OR 97331 United States
AU: Bond, B J
EM: barbara.bond@oregonstate.edu
AF: Washington State University, Department of Civil and Environmental Engineering, Pullman, WA 99164 United States
AB: Ecosystem carbon dynamics in flat, uniform terrain are commonly studied using standard micrometeorological techniques such as eddy covariance or gradient methods. But many of the world's ecosystems are in complex topography that is inappropriate for these methods. Nocturnal cold air drainage commonly occurs in mountainous terrain. This drainage provides an opportunity to monitor ecosystem carbon dynamics because as air flows downhill through a watershed, it collects respired CO₂ from the soil and vegetation. If the nocturnal drainage can be treated as a river of air flowing down a valley, sampling this air from a tower at the base of a watershed could provide an estimate of ecosystem respiration and the ¹²C/¹³C ratio. To interpret the measured CO₂ and the ¹²C/¹³C ratio, the characteristics of the drainage and the footprint (source area) of air passing the tower must be understood. To explore the potential of using nocturnal cold air drainage we built a 37 m tower at the base of a deeply incised watershed of ~40 y-old Douglas-fir in the Oregon Cascades. At various heights on the tower we monitored air temperature, wind speed/direction, and the CO₂ concentration and ¹²C/¹³C isotopic ratio with a combination of thermistors, sonic anemometers (2-D and 3-D) and a CO₂ profile system. The temperature gradient along the axis of the watershed was monitored by 30 temperature sensors from the base to the top of the watershed. The maximum drainage windspeeds on the tower occurred near sunset and, unlike past reports of cold air drainage, this drainage was very deep (> 37 m). The drainage became well mixed when the vertical profile of potential temperature became isothermal. It remained well mixed through the night into the early morning. The drainage occurred on most summer nights and typically provided a range of CO₂ (> 60 ppm) sufficient for "Keeling plot" analysis. In September 2005, we released a tracer in the watershed (SF6) to determine the varying footprint size of the tower. The footprint size and windspeed varied throughout the night, resulting in a change in the CO₂ concentration at the tower. Further analysis will determine how the CO₂ passing the tower is altered by entrainment of the air overlying the drainage and the change in the source area of the drainage.
DE: 0416 Biogeophysics
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0452 Instruments and techniques
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: Fall Meeting 2005