Quantifying Isentropic Transport and Mixing in a Modified Lagrangian Coordinate: Applications to Rossby Wave Breaking

Isentropic transport and mixing are important processes for the distribution of chemical constituents in the mid-to-high latitudes. A new framework is introduced to quantify both isentropic transport and isentropic mixing in a modified Lagrangian coordinate. The framework is applied to quantify the transport and mixing associated with the two types of Rossby wave breaking (i.e. cyclonic and anticyclonic) in a hierarchy of numerical simulations. All these simulations show that cyclonic wave breaking (CWB) exhibits either comparable or stronger transport and mixing than anticyclonic wave breaking (AWB). Since CWB occurs less frequently when the jet shifts poleward while AWB occurs more frequently, this asymmetry in the transport/mixing associated with the two types of Rossby wave breaking translates into a change in total isentropic transport/mixing when the jet shifts. This dynamical relationship between the jet and the transport/mixing is relevant not only for internal climate variability such as the El-Niño Southern Oscillation (ENSO) and the annular modes, but also, for future climate change that may drive changes in the jet position.