Abstract
The ability of current global models to simulate the transport of
CO2 by mid-latitude, synoptic-scale weather systems
(i.e. CO2 weather) is important for inverse estimates of
regional and global carbon budgets but remains unclear without
comparisons to targeted measurements. Here, we evaluate ten models that
participated in the Orbiting Carbon Observatory-2 model intercomparison
project (OCO-2 MIP version 9) with intensive aircraft measurements
collected from the Atmospheric Carbon Transport (ACT)-America mission.
We quantify model-data differences in the spatial variability of
CO2 mole fractions, mean winds, and boundary layer
depths in 27 mid-latitude cyclones spanning four seasons over the
central and eastern United States. We find that the OCO-2 MIP models are
able to simulate observed CO2 frontal differences with
varying degrees of success in summer and spring, and most underestimate
frontal differences in winter and autumn. The models may underestimate
the observed boundary layer-to-free troposphere CO2
differences in spring and autumn due to model errors in boundary layer
height. Attribution of the causes of model biases in other seasons
remains elusive. Transport errors, prior fluxes, and/or inversion
algorithms appear to be the primary cause of these biases since model
performance is not highly sensitive to the CO2 data used
in the inversion. The metrics presented here provide new benchmarks
regarding the ability of atmospheric inversion systems to reproduce the
CO2 structure of mid-latitude weather systems.
Controlled experiments are needed to link these metrics more directly to
the accuracy of regional or global flux estimates.