Carbon dioxide uptake of a forested region in southwest France derived from airborne CO₂ and CO measurements in a quasi‐Lagrangian experiment

Abstract

[1] This paper presents a Lagrangian budgeting approach to quantify the uptake of CO 2 by vegetation at horizontal scales of several tens of kilometers. For this purpose, CO 2 and meteorological parameters were measured from a small aircraft during four flights in June 2001 over a flat homogeneous and productive temperate forest in the Landes region (southwestern France). Additional CO measurements were made in order to identify and quantify the potential influence of anthropogenic emissions on the net CO 2 flux derived from the measurements. For one of four flights, Lagrangian conditions were nearly perfectly fulfilled. On average, the CO 2 mixing ratio in the boundary layer decreased at a rate of 0.11 ppm km À1 , yielding an average CO 2 uptake by the forest of 16 ± 2.5 mmol m À2 s À1 between 1230 and 1430 UT. Our result is about 15% smaller than the local net ecosystem exchange measured by eddy covariance at a tower north of the flight domain and about 12% higher than a regional estimate based on remote sensing data for the whole experimental area. The contribution of anthropogenic emissions to the regional CO 2 budget was estimated from the CO measurements to be to <0.5 mmol m À2 s À1 .

Error correlation between CO&lt;sub&gt;2&lt;/sub&gt; and CO as constraint for CO&lt;sub&gt;2&lt;/sub&gt; flux inversions using satellite data

“…If model transport errors for CO 2 and CO are correlated, then CO has the potential to provide additional information to improve inverse CO 2 flux estimates (Palmer et al, 2006). Strong correlations between CO 2 and CO concentrations are consistently seen in atmospheric observations at the surface (Potosnak et al, 1999;Gamnitzer et al, 2006) and from aircraft (Conway et al, 1993;Sawa et al, 2004;Schmitgen et al, 2004;Suntharalingam et al, 2004;Takegawa et al, 2004;Palmer et al, 2006). These correlations result from common source/sink regions, common large-scale latitudinal gradients, and common transport.…”

CO&lt;sub&gt;2&lt;/sub&gt; budgeting at the regional scale using a Lagrangian experimental strategy and meso-scale modeling

“…The CO 2 surface fluxes obtained by the three methods vary between 10 and 16 µmol.m −2 .s −1 , values lower than the fluxes estimated by Gibert et al (2007), over a region dominated by winter crops in May, and by Schmitgen et al (2004), in the Landes in June, which were 20 and 16 µmol.m −2 .s −1 , respectively.…”

“…The main parameters concerning the carbon cycle in the model are the g mes and RE 25 parameters. A specific calibration was done for these parameters, using data from previous campaigns dedicated to atmospheric regional CO 2 , as the COCA Experiment in the Landes forest, 2001 (Schmitgen et al, 2004) and RE-CAB in Netherlands andSpain in 2003 (Pérez-Landa et al, 2007). These datasets offered the opportunity to calibrate these two parameters against CO 2 surface fluxes and atmospheric concentration.…”

“…Schmitgen et al (2004) already showed the potential of a Lagrangian budgeting approach for accurately estimating CO 2 fluxes for the Landes region, using the aircraft Lagrangian observations and a simple Lagrangian model.…”

Assessing the regional surface influence through Backward Lagrangian Dispersion Models for aircraft CO&lt;sub&gt;2&lt;/sub&gt; vertical profiles observations in NE Spain

“…Bakwin et al, 2003), from aircraft vertical sampling (Wofsy et al, 1988;Lloyd et al, 2001;Font et al, 2010) or by performing Lagrangian boundary layer budget campaigns (Schmitgen et al, 2004;Martins et al, 2009;Sarrat et al, 2009). The estimation of the regional surface fluxes based on a single tall tower is restrained by the influence of local fluxes (of up to 50 km distance) .…”