Understanding Mid-Latitude Jet Variability and Change using Rossby Wave Chromatography: Methodology

Rossby Wave Chromatography (RWC) is implemented in a linearized barotropic model as a tool to diagnose and understand the interaction between the mid-latitude jet and the eddies. Given the background zonal-mean flow and the space-time structure of the baroclinic wave activity source, RWC calculates the space-time structure of the upper tropospheric eddy momentum fluxes. Using the convergence of the vertical EP flux in the upper troposphere as the wave source, RWC reproduces the main features of a GCM’s mean state and response to external forcing. When coupled to the zonal-mean zonal wind and a simple model of wave activity source phase speed changes RWC also simulates the temporal evolution of the GCM’s internally generated zonal-mean zonal wind anomalies. Because the full space-time structure of the baroclinic wave activity source is decoupled from the background flow, RWC can be used to isolate and quantify the dynamical mechanisms responsible for 1) the poleward shift of the mid-latitude jet and 2) the feedbacks between the eddy momentum fluxes and the background flow in general.