The rates of descent of middle atmospheric (stratosphere and mesosphere) air above the winter poles are often derived using trace gas measurements made by remote sounding instruments. The derivations are based on the assumption that vertical motion of air above the poles is the predominant cause of changes in the concentration of the gas.
To ascertain how well the above assumption holds, the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM) is used over several recent winters to separate the processes affecting CO concentrations in the polar middle atmosphere. Ground-based and satellite data are used to evaluate how different are the derived descent rates, when accounting for influences other than pure vertical motion. The results indicate errors on the same scale as the measured rates, and often a misinterpretation of the direction of air motion.