Differences between surface and column atmospheric CO_2 and implications for carbon cycle research

We used a three‐dimensional atmospheric transport model to investigate several aspects of column CO_2 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 CO_2 had less variability than surface CO_2 on all scales. The annual mean column CO_2 north‐south gradient and seasonal cycle amplitude were approximately one half of their surface counterparts and the column CO_2 diurnal amplitude rarely exceeded 1 ppm. A 1 Gt C yr^(−1) Northern Hemisphere carbon sink decreased the north‐south column CO_2 gradient by ∼0.4 ppm