Moist synoptic transport of CO2 along the mid‐latitude storm track

Atmospheric mixing ratios of CO 2 are strongly seasonal in the Arctic due to mid‐latitude transport. Here we analyze the seasonal influence of moist synoptic storms by diagnosing CO 2 transport from a global model on moist isentropes (to represent parcel trajectories through stormtracks) and parsing transport into eddy and mean components. During winter when northern plants respire, warm moist air, high in CO 2 , is swept poleward into the polar vortex, while cold dry air, low in CO 2 , that had been transported into the polar vortex earlier in the year is swept equatorward. Eddies reduce seasonality in mid‐latitudes by ∼50% of NEE (∼100% of fossil fuel) while amplifying seasonality at high latitudes. Transport along stormtracks is correlated with rising, moist, cloudy air, which systematically hides this CO 2 transport from satellites. We recommend that (1) regional inversions carefully account for meridional transport and (2) inversion models represent moist and frontal processes with high fidelity.