INTERCOMPARISON AMONG CHAMBER, TOWER, AND AIRCRAFT NET CO2 AND ENERGYFLUXES MEASURED DURING THE ARCTIC SYSTEM SCIENCE LAND-ATMOSPHERE-ICE INTERACTIONS (ARCSS-LAII) FLUX STUDY

Measurements of net ecosystem CO2 exchange (NEE) and energy balance we re made using chamber-, tower-, and aircraft-based measurement techniq ues in Alaskan arctic tundra ecosystems during the 1994-1995 growing s easons (June-August). One of our objectives was to quantify the interr elationships between the NEE and the energy balance measurements made from different sampling techniques. Qualitative and quantitative inter comparisons revealed that on average the correspondence between the ma ss and energy fluxes measured by these sampling methods was good despi te potential spatial and temporal mismatches in sampling scale. Quanti tative comparisons using least squares linear regression analyses with the tower-based measurements of NEE as the independent variable indic ate that the chamber- and aircraft-based NEE measurements were general ly lower relative to the tower-based measurements (slope = 0.76-0.86). Similarly, tower-aircraft comparisons of latent (L-e) and sensible (H ) heat exchange indicated that the aircraft-based measurements were lo wer than the tower-based measurements (slope = 0.72-0.80). Qualitative comparisons, however, indicate that the correspondence among the cham ber-, tower-: and aircraft-measured fluxes varied both seasonally and interannually, suggesting the lack of a consistent bias between the sa mpling techniques. The results suggest that differences observed betwe en the chamber, tower, and aircraft flux measurements were primarily d ue to the failure to account for the spatial distribution of surface t ypes in the tower and aircraft sampling footprint, problems involved i n the comparison of temporal and spatial averages, and temporal (e.g., seasonal and interannual) variance in rates of mass and energy flux f or a given point. Other potential sources of variance include the unde restimation of nocturnal NEE by the tower-based eddy covariance system , and the periodic occurrence of an elevated CO2 plume in the atmosphe re over the Prudhoe Bay oil field. Even with these potential sources o f variation, the results reveal that the various methods,give comparab le estimates of NEE and energy flux within a range of temporal or spat ial variability.