Differences between surface and column atmospheric CO₂ and implications for carbon cycle research

[1] We used a three-dimensional atmospheric transport model to investigate several aspects of column CO₂ that are important for the design of new satellite-based observation systems and for the interpretation of observations collected by Sun-viewing spectrometers. These aspects included the amplitude of the diurnal cycle and how it is related to surface fluxes, the amplitude and phase of the seasonal cycle, and the magnitude of the north-south hemispheric gradient. In our simulation, we found that column CO₂ had less variability than surface CO₂ on all scales. The annual mean column CO₂ north-south gradient and seasonal cycle amplitude were approximately one half of their surface counterparts and the column CO₂ diurnal amplitude rarely exceeded 1 ppm. A 1 Gt C yr⁻¹ Northern Hemisphere carbon sink decreased the north-south column CO₂ gradient by ∼0.4 ppm.