Characterization of Regional‐Scale CO 2 Transport Uncertainties in an Ensemble with Flow‐Dependent Transport Errors

Abstract Inference of CO 2 surface fluxes using atmospheric CO 2 observations in atmospheric inversions depends critically on accurate representation of atmospheric transport. Here we characterize regional‐scale CO 2 transport uncertainties due to uncertainties in meteorological fields using a mesoscale atmospheric model and an ensemble of simulations with flow‐dependent transport errors. During a 1‐month summer period over North America, transport uncertainties yield an ensemble spread in instantaneous CO 2 at 100 m above ground level comparable to the CO 2 uncertainties resulting from 48% relative uncertainty in 3‐hourly natural CO 2 fluxes. Temporal averaging reduces transport uncertainties but increases the influence of CO 2 uncertainties from the lateral boundaries. The influence of CO 2 background uncertainties is especially large for column‐averaged CO 2 . These results suggest that transport errors and CO 2 background errors limit regional atmospheric inversions at two distinct timescales and that the error characteristics of transport and background errors should guide the design of regional inversion systems