A Numerical Study of the Influence of a Clearcut on Eddy-Covariance Fluxes of CO2 Measured Above a Forest

Journal Article · Wed Sep 03 04:00:00 EDT 2008 · Agricultural and Forest Meteorology, 148(10):1488-1500

DOI:https://doi.org/10.1016/j.agrformet.2008.05.009· OSTI ID:947047

Wang, Weiguo; Davis, Kenneth J

We compare the contributions of unit source fluxes over a clear-cutting area in a forest and over the contiguous forested area to the eddy-covariance (EC) flux of CO2 measured at a tower standing in the center of the clearcut under daytime convective conditions. The large-eddy simulation (LES) technique is used to simulate the dispersion and transport of two conservative and passive tracers that are released from the clearcut and from the forested area, respectively. The time series of the LES-generated vertical velocity and the mixing ratios of both tracers on all the levels at the tower location are recorded every model time step during the last hour of each LES run; this somewhat mimics real EC flux measurements at the tower. The contribution of the unit surface flux over the clearcut relative to that over the forested area decreases exponentially with increasing measurement height, decreasing convective boundary layer depth, increasing atmospheric stability, and decreasing size of the clearcut. LES-derived results are fitted to an empirical relation and applied to flux measurements at the 447-m tall tower in Wisconsin, USA. The contribution of the unit flux over the clearcut on the EC flux measured at the 30-m level of the tower is larger than 50% of that over the forested area under most unstable conditions, while smaller than 2.5% at the 396-m level. Existing analytical footprint models are inappropriate to address the clearcut influence due to clearcut-induced heterogeneity of the turbulent flow in the tower area.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 947047
• Report Number(s): PNNL-SA-60931
• Journal Information: Agricultural and Forest Meteorology, 148(10):1488-1500, Journal Name: Agricultural and Forest Meteorology, 148(10):1488-1500 Journal Issue: 10 Vol. 148; ISSN AFMEEB; ISSN 0168-1923
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
BOUNDARY LAYERS
CARBON DIOXIDE
COMPUTERIZED SIMULATION
ECOLOGICAL CONCENTRATION
FORESTS
HARVESTING
TRACER TECHNIQUES
TURBULENT FLOW
clearcut
eddy-covariance flux
footprint
heterogeneous flow
large-eddy simulation