20 Years of Tracer Transport Studies: Challenges and Implications for Flux Inversions

This presentation demonstrates that different chemistry transport models (CTMs), each extensively validated, can have significant differences in the predicted transport of long-lived trace gases. For carbon dioxide (CO2), this difference is 0.5 ppm or greater in the total column, The value exceeds the nominal retrieval error requirements of the Total Carbon Column Observing Network (TCCON) and the Orbiting Carbon Observatory 2 (OCO-2), which were chosen based on the understanding of the accuracy necessary to infer surface fluxes of CO2 on regional and seasonal scales. This suggests that the transport errors of CTMs play a considerable role in the surface flux inversion of satellite-based measurements of long-lived trace gases and the interpretation of the inferred fluxes requires a careful understanding of this role. Here, we use observations of sulfur hexafluoride (SF6) to evaluate the transport models, in particular their vertical and horizontal gradients, in an effort to ultimately reduce the uncertainty in CO2 predictions.