Abstract
Abstract. We investigate factors that drive the variability in total column CO2 at the Total Carbon Column Observing Network sites in the Southern Hemisphere using fluxes tagged by process and by source region from the CarbonTracker analysed product as well as the Simple Biosphere model. We show that the terrestrial biosphere is the largest driver of variability in the Southern Hemisphere column CO2. However, it does not dominate in the same fashion as in the Northern Hemisphere. Local- and hemispheric-scale biomass burning can also play an important role, particularly at the tropical site, Darwin. The magnitude of seasonal variability in the column-average dry-air mole fraction of CO2, XCO2, is also much smaller in the Southern Hemisphere and comparable in magnitude to the annual increase. Comparison of measurements to the model simulations highlights that there is some discrepancy between the two time series, especially in the early part of the Darwin data record. We show that this mismatch is most likely due to erroneously estimated local fluxes in the Australian tropical region, which are associated with enhanced photosynthesis caused by early rainfall during the tropical monsoon season.
Highlights
Anthropogenic emissions of carbon dioxide (CO2) are the most important driver of human-induced climate change
Through assessment of CO2 tracers tagged by region and process, we have examined the drivers of variability in XCO2 at the Southern Hemisphere Total Carbon Column Observing Network (TCCON) sites
At Lauder and Wollongong the remote terrestrial biosphere signals are of the order of 0.6 μmol mol−1, while at Wollongong the Australian region contributes a signal of a similar magnitude
Summary
Anthropogenic emissions of carbon dioxide (CO2) are the most important driver of human-induced climate change. Column measurements can potentially provide information on remote locations, because they are influenced by a larger spatial area than surface in situ measurements (Keppel-Aleks et al, 2011) This comes at the expense of potentially more-detailed information about local fluxes. Basu et al (2011) show an underestimate of the modelled seasonal cycle magnitude with CarbonTracker when compared to northern hemispheric TCCON data, a robust finding with those flux estimates regardless of the transport model used. We examine the variability at the Southern Hemisphere TCCON sites via comparison of the measurements with simulations from the CarbonTracker data assimilation system (Peters et al, 2007) and a separate tagged tracer model run, both driven by the same bestestimate fluxes of CO2 to and from the atmosphere.
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