Abstract
Abstract. We evaluate three estimates of the atmosphere-biosphere exchange against total column CO2 observations from the Total Carbon Column Observing Network (TCCON). Using the GEOS-Chem transport model, we produce forward simulations of atmospheric CO2 concentrations for the 2006–2010 time period using the Carnegie-Ames-Stanford Approach (CASA), the Simple Biosphere (SiB) and the GBiome-BGC models. Large differences in the CO2 simulations result from the choice of the atmosphere-biosphere model. We evaluate the seasonal cycle phase, amplitude and shape of the simulations. The version of CASA currently used as the a priori model by the GEOS-Chem carbon cycle community poorly represents the season cycle in total column CO2. Consistent with earlier studies, enhancing the CO2 uptake in the boreal forest and shifting the onset of the growing season earlier significantly improve the simulated seasonal CO2 cycle using CASA estimates. The SiB model gives a better representation of the seasonal cycle dynamics. The difference in the seasonality of net ecosystem exchange (NEE) between these models is not the absolute gross primary productivity (GPP), but rather the differential phasing of ecosystem respiration (RE) with respect to GPP between these models.
Highlights
An accurate estimation of carbon fluxes is a central goal of the carbon cycle community
We investigate a simulation with CASA, but with uptake enhanced in the boreal forest and with the onset of the growing season shifted according to Keppel-Aleks et al (2012)
Goddard Earth Observing System (GEOS)-Chem CO2 simulations using year-specific SiB NEE estimations or only SiB 2009 NEE estimations are a significant improvement compared to simulations with the standard CASA climatology, currently used within the GEOSChem simulation
Summary
An accurate estimation of carbon fluxes is a central goal of the carbon cycle community. Such estimates have been derived on small spatial scales using direct measures of the provides excellent constraints at local and regional scales. Keppel-Aleks et al (2012) estimated the north–south CO2 gradient using total column measurements from the TCCON by correlating the CO2 abundSanocleisdtoEthaermthid-tropospheric potential temperature, which serves as a dynamical tracer. J. Messerschmidt et al.: Atmosphere–biosphere exchange estimations with TCCON measurements
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