1California Institute of Technology, Pasadena, CA, USA
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
3University of Bremen, Bremen, Germany
4Department of Earth System Science, University of California, Irvine, California, USA
Abstract. We observe significant interannual variability in the strength of the seasonal cycle drawdown in northern midlatitudes from measurements of CO2 made by the Total Carbon Column Observing Network (TCCON) and the Greenhouse Gases Observing Satellite (GOSAT). This variability correlates with surface temperature in the boreal latitudes. The TCCON measurements give an average covariation between the XCO2 seasonal cycle minima and boreal surface temperature of 1.3 ± 0.7 ppm K−1. Assimilations from CarbonTracker 2011 and CO2 simulations using the Simple Biosphere exchange Model (SiB) transported by GEOS-Chem underestimate this covariation. Both atmospheric transport and biospheric activity contribute to the observed covariation.