دانلود رایگان مقاله شناسایی فرارفت CO2 بر روی شیب تپه با استفاده از جریان اطلاعات

Abstract

In hilly terrain affected by drainage flow, the horizontal advection of CO2 makes it difficult to accurately observe the net ecosystem exchange of CO2 by the eddy covariance technique. Downslope drainage can result in an overestimation of respiration at the bottom of a hill slope and an underestimation at the top, resulting in discrepancies among different flux corrections using filters based on the friction velocity, light response curve, and timing of advection. Vertical profiles of the CO2 concentration from the ground to above the canopy were measured along with above-canopy EC flux measurements at the top and bottom of a hill slope at the Gwangneung KoFlux sites from 2008 to 2010. To infer the timing, direction, temporal scale, and structure of CO2 advection from uphill to downhill, we constructed an information flow dynamical process network (DPN) based on the observed multi-level CO2 concentrations. A site-specific quality control filter was developed to eliminate data strongly affected by CO2 advection, which identifies the observations when strong downslope information flow exists in the DPN. This site-specific filter considerably reduced the discrepancies among different traditional flux corrections. This research provides a method for the general characterization of advection using information flow, and application of the method as a site-specific filter for eddy covariance observations in hilly and complex terrain.

4. Summary and conclusions

This study provides a method for applying the information flow DPN approach to ascertain the advection of CO2 via drainage flow at a hill slope tower site. Vertical profile measurements of CO2 concentrations at two tower sites demonstrated the following: (1) different patterns of CO2 concentrations between the uphill and downhill site at night, (2) an underestimation (overestimation) of the NEE peaks around sunset for the uphill (downhill) site, and (3) asymmetric magnitudes of FCO2 Obs around sunset and sunrise. Based on these results, we identified that (1) the drained CO2 from the uphill site banks up to the downhill site and (2) the CO2 drainage continues until early morning, when the valley wind blows. Using the information flow DPN, we have delineated the characteristics of CO2 drainage such as timing, temporal scale, direction, and structure. The key findings include the following: (1) the drained CO2 strongly accumulates from 17:00 to 21:00 regardless of season; (2) the primary timescale of that drainage process is one half hour; (3) the accumulated CO2 does not dissipate uphill; (4) the more the canopy develops, the more clearly the CO2 flows are divided into two parts, i.e., above and below the canopy; and (5) the traditional u* threshold can successfully filter out the drainageaffected data from 17:00 to 21:00.