Impact of finite-amplitude eddy-zonal flow interaction on the transport characteristics in the upper troposphere

The upper-tropospheric zonal wind experiences a transition from a subtropical jet and an eddy-driven jet in winter to a merged eddy-driven jet in summer throughout the seasonal cycle. This transition takes place rapidly in late spring and early summer, associated with a change in atmospheric transport near the jet core, from a robust mixing barrier to a leaky barrier and from up-gradient eddy potential vorticity flux to down-gradient eddy flux. Despite the observed transport characteristics, the underlying mechanisms and the implications for chemical transport have not been fully elucidated.

The transport characteristics will be investigated in a hierarchy of models, with a specified dynamics (SD) version of WACCM, a dry atmospheric dynamical core, and a shallow water model of the upper troposphere. A finite-amplitude wave activity diagnostic will be used to evaluate the separate roles of transient wave activity, isentropic mixing and adiabatic circulation in the seasonal cycle of eddy potential vorticity fluxes and tracer transport.