Isentropic Diffusion Coefficient Derived from Chemical Constituent Data

The isentropic diffusion coefficient (K-yy) characterizes large-scale atmospheric mixing processes. Chemical constituents allow us to directly estimate K-yy from observational data sets. This study investigates general aspects of the mixing processes from a systematic survey of the common features and constituent dependency of K-yy. Analysis with chemical constituent data obtained from a global chemical transport model demonstrates that long-lived species whose chemical lifetimes (tau) are several years long have very common seasonal and latitudinal variations of K-yy, which is considered to represent actual atmospheric mixing. K-yy, estimated from chemical species with tau shorter than several weeks, becomes considerably greater than that from long-lived species and indicates the significance of non-linear effects. Meridional transport analysis also investigates that shorter tau results in greater spatial constituent variations and larger contributions of the eddy compared to the mean motions in the constituent transport flux.