The seasonal cycle of atmospheric CO2 in the southern hemisphere over the last ten years seen by GOSAT

Abstract

<p>In the southern hemisphere, the sparse coverage of in-situ CO<sub>2</sub> measurements prevents a robust determination of regional carbon fluxes and leads to large uncertainties in inverse model results. Therefore, the extensive spatial coverage afforded by satellite CO<sub>2</sub> measurements is especially valuable there. By analyzing satellite measurements, new insights on the carbon cycle can be derived and carbon cycle models can be validated for the southern hemisphere.</p><p>Here, we present a comparison of atmospheric CO<sub>2</sub> data in Australia provided by the Greenhouse gases Observing SATellite (GOSAT) and the CarbonTracker (CT2019) inverse model from 2009 to 2018. We find that the seasonality of GOSAT CO<sub>2</sub> is different from that of CarbonTracker across much of the southern hemisphere. This discrepancy follows a clear seasonal pattern with the largest difference of ~2ppm between October and December. We investigate the origin of the discrepancy by utilizing the CO<sub>2</sub> components provided by CarbonTracker and different fire CO<sub>2</sub> emission databases. Further, we conduct several sensitivity studies by assimilating GOSAT CO<sub>2</sub> in the TM5-4DVar data assimilation system, and by transporting different surface fluxes through the TM5 transport model. Our results suggest that the underestimation of local and transported wildfire CO<sub>2</sub> emissions could cause the observed discrepancy in the seasonality of column CO<sub>2</sub> between GOSAT and inverse models such as CarbonTracker in the southern hemisphere.</p>