Isentropic Diffusion Coefficient Derived from Chemical Constituent Data

Abstract

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 (τ) 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 τ shorter than several weeks, becomes considerably greater than that from long-lived species and indicates the significance of nonlinear effects. Meridional transport analysis also investigates that shorter τ results in greater spatial constituent variations and larger contributions of the eddy compared to the mean motions in the constituent transport flux.