Estimating Asian terrestrial carbon fluxes from CONTRAIL aircraft and surface CO<sub>2</sub> observations for the period 2006–2010

Abstract

Abstract. Current estimates of the terrestrial carbon fluxes in Asia show large uncertainties particularly in the boreal and mid-latitudes and in China. In this paper, we present an updated carbon flux estimate for Asia ("Asia" refers to lands as far west as the Urals and is divided into boreal Eurasia, temperate Eurasia and tropical Asia based on TransCom regions) by introducing aircraft CO 2 measurements from the CONTRAIL (Comprehensive Observation Network for Trace gases by Airline) program into an inversion modeling system based on the CarbonTracker framework. We estimated the averaged annual total Asian terrestrial land CO 2 sink was about −1.56 Pg C yr −1 over the period 2006-2010, which offsets about one-third of the fossil fuel emission from Asia (+4.15 Pg C yr −1 ). The uncertainty of the terrestrial uptake estimate was derived from a set of sensitivity tests and ranged from −1.07 to −1.80 Pg C yr −1 , comparable to the formal Gaussian error of ±1.18 Pg C yr −1 (1-sigma). The largest sink was found in forests, predominantly in coniferous forests (−0.64 ± 0.70 Pg C yr −1 ) and mixed forests (−0.14 ± 0.27 Pg C yr −1 ); and the second and third large carbon sinks were found in grass/shrub lands and croplands, accounting for −0.44 ± 0.48 Pg C yr −1 and −0.20 ± 0.48 Pg C yr −1 , respectively. The carbon fluxes per ecosystem type have large a priori Gaussian uncertainties, and the reduction of uncertainty based on assimilation of sparse observations over Asia is modest (8.7-25.5 %) for most individual ecosystems. The ecosystem flux adjustments follow the detailed a priori spatial patterns by design, which further increases the reliance on the a priori biosphere exchange model. The peak-to-peak amplitude of inter-annual variability (IAV) was 0.57 Pg C yr −1 ranging from −1.71 Pg C yr −1 to −2.28 Pg C yr −1 . The IAV analysis reveals that the Asian CO 2 sink was sensitive to climate variations, with the lowest uptake in 2010 concurrent with a summer flood and autumn drought and the largest CO 2 sink in 2009 owing to favorable temperature and plentifulPublished by Copernicus Publications on behalf of the European Geosciences Union. 5808 H. F. Zhang et al.: Estimating Asian terrestrial carbon fluxes precipitation conditions. We also found the inclusion of the CONTRAIL data in the inversion modeling system reduced the uncertainty by 11 % over the whole Asian region, with a large reduction in the southeast of boreal Eurasia, southeast of temperate Eurasia and most tropical Asian areas.

Impact of Siberian observations on the optimization of surface CO<sub>2</sub> flux

“…The results show that surface CO 2 uptake over the Eurasian boreal (EB) region slightly increases from −0.96 to −1.02 Pg C yr −1 for the period 2006-2010 when aircraft CO 2 measurements were assimilated. However, the surface measurement data over the EB region are still not used in the study by Zhang et al (2014b). Using an influence matrix calculation, Kim et al (2014b) showed that comprehensive coverage of additional observations in an observation-sparse region, e.g., Siberia, is necessary to estimate the surface CO 2 flux in these areas as accurately as that obtained for North America in the CarbonTracker framework.…”

“…The site categories and MDM values are assigned the same value as in previous studies (Peters et al, 2007;Kim et al, 2014b;Zhang et al, 2014b): marine boundary layer (0.75 ppm), continental sites (2.5 ppm), mixed land/ocean and mountain sites (1.5 ppm), continuous sites (3.0 ppm), and difficult sites (7.5 ppm) that are located near polluted areas with high anthropogenic CO 2 emissions. The continuous site category is generally used for observations measured continuously.…”

“…Schneising et al (2011) showed that SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) retrieval data indicate a stronger North American boreal forest uptake and weaker Russian boreal forest uptake compared to CarbonTracker within their uncertainties. On the other hand, Zhang et al (2014b) estimated surface CO 2 fluxes in Asia by assimilating CONTRAIL (Machida et al, 2008) aircraft CO 2 measurements into the CarbonTracker framework. The CON-TRAIL measurements include ascending/descending vertical profiles and cruise data below tropopause.…”

AirCore-HR: a high-resolution column sampling to enhance the vertical description of CH<sub>4</sub> and CO<sub>2</sub>

“…Other, less regular aircraft campaigns are also dedicated to study GHG at a local scale (Zhang et al, 2014;Chen et al, 2010;Karion et al, 2013;Crevoisier et al, 2006Crevoisier et al, , 2010Sweeney et al, 2015) or from pole to pole such as the HIPPO project (Wofsy, 2011). Such vertical profiles are usually limited to 12 km.…”

Influence of CO<sub>2</sub> observations on the optimized CO<sub>2</sub> flux in an ensemble Kalman filter

“…Kim et al (2014) showed that the estimates of the surface CO 2 flux are more consistent with observed CO 2 concentrations in Asia when using the nesting domain of the transport model on Asia in CarbonTracker. Zhang et al (2014) conducted a study on the assimilation of aircraft CO 2 observations from the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL; Machida et al, 2008) in Asia using CarbonTracker.…”