HR: 1340h
AN: B23A-0916    [Abstracts]
TI: Spatial and temporal variation in nighttime atmospheric carbon dioxide profiles in mountainous terrain.
AU: * Warrens, N
EM: newarrens@noctrl.edu
AF: North Central College, Department of Physics, Naperville, IL 60540, United States
AU: Blecker, S W
EM: sblecker@uidaho.edu
AF: University of Idaho, Department of Forest Resources, Moscow, ID 83844, United States
AU: Kavanagh, K
EM: katyk@uidaho.edu
AF: University of Idaho, Department of Forest Resources, Moscow, ID 83844, United States
AB: On clear nights cold air sinks in mountainous terrain. This nocturnal cold air drainage contains high levels of respired CO₂ that can be used to assess nighttime respiration rates and estimates of ecosystem water use efficiency. However, the depth and concentration of CO₂ in this cold air pool likely varies with slope position, valley morphology, elevation, and time of night. We used a tethered helium balloon and attached tubing to investigate the CO₂ concentration in the nocturnal cold air drainage flowing from two constrained forested watersheds in Northern Idaho. We monitored air temperature and CO₂ concentration from 1m to 200m throughout the summer from dusk to dawn. At both sites, the inversion was deep, frequently reaching 100-150m, with observed lapse rates of 40-50 °C/km compared to more typical lapse rates of -6.5 °C/km in the absence of temperature inversions. At Mica Creek, the CO₂ concentrations ranged from approx. 385 ppm at the top of the profile to 460 ppm at 1m, whereas, CO₂ concentrations generally ranged from 375 ppm at the top of the profile to 500 ppm at 1m at Benton Creek. Temporal sampling indicated that CO₂ concentrations were steady during the night at Mica Cr but they increased by about 50-60ppm at Benton Cr throughout the night. Interestingly, the increased CO₂ concentrations, relative to ambient, exceeded the depth of the cold air pool at Benton Cr. These data indicate that spatial and temporal patterns in nocturnal CO₂ concentrations varied depending if the cold air flowed like a river during the night or if a lake formed. CO₂ concentrations remained steady all night in the river of cold air but steadily increased on the site where a lake formed. These results will be used to develop and test models describing cold air flow in complex terrain and to better assess the suitability of using cold air drainage to assess ecosystem processes.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0438 Diel, seasonal, and annual cycles (4227)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting