A new procedure to obtain a longitudinally varying and slowly evolving
atmospheric background state for the analysis of Rossby waveguides is
described and discussed. The procedure is a rolling zonalization scheme,
redistributing Ertel potential vorticity in a moving window to separate
waves from the background. Waveguides are subsequently diagnosed from
the gradient of the logarithm of potential vorticity. The effectiveness
of the wave-background separation, even in large-amplitude conditions,
is illustrated with reanalysis data. Established climatological mean
waveguide structures are recovered from the rolling-zonalized state in
the limit of long-term aggregation. Two contrasting episodes of Rossby
wave packet propagation demonstrate how the evolution of waveguides
derived from rolling zonalization can correspond to the development of
superposed wave packets. The ability of the procedure to work with
snapshots of the atmosphere provides new opportunities for waveguide
research.