Technical Note: Latitude-time variations of atmospheric column-average dry air mole fractions of CO.sub.2, CH.sub.4 and N.sub.2O

We present a comparison of an atmospheric general circulation model (AGCM)-based chemistry-transport model (ACTM) simulation with total column measurements of CO.sub.2, CH.sub.4 and N.sub.2 O from the Total Carbon Column Observing Network (TCCON). The model is able to capture observed trends, seasonal cycles and inter hemispheric gradients at most sampled locations for all three species. The model-observation agreements are best for CO.sub.2, because the simulation uses fossil fuel inventories and an inverse model estimate of non-fossil fuel fluxes. The ACTM captures much of the observed seasonal variability in CO.sub.2 and N.sub.2 O total columns (~81 % variance, R0.9 between ACTM and TCCON for 19 out of 22 cases). These results suggest that the transport processes in troposphere and stratosphere are well represented in ACTM. Thus the poor correlation between simulated and observed CH.sub.4 total columns, particularly at tropical and extra-tropical sites, have been attributed to the uncertainties in surface emissions and loss by hydroxyl radicals. While the upward-looking total column measurements of CO.sub.2 contains surface flux signals at various spatial and temporal scales, the N.sub.2 O measurements are strongly affected by the concentration variations in the upper troposphere and stratosphere.