Rossby waves orchestrate midlatitude weather systems and the group propagation within Rossby wave trains governs large-scale energy transfer along jet streams. Rossby wave trains are fundamental to the predictability of the midlatitude atmosphere and have found recent attention as precursors to high-impact weather events.

A current PhD project (by Franziska Gierth) develops a methodology to quanitfy the relative importance of different processes in Rossby wave group propagation. Preliminary results indicate that baroclinic coupling and upper-level divergent flow - primarily associated with latent heat release below - is as important as quasi-barotropic wave propagation itself. This increased complexity of the processes involved has ramifications for predictability that are currently under investigation.

A recent Master thesis (by Marlene Baumgart) employed the partitioning developed by Franziska Gierth to quantify contributions to PV forecast errors along the midlatitude Rossby wave guide. The material tendency equation for the PV error derived by Davies and Didone (2013) has been evaluated for a poorly-forecast breaking wave over Europe. The results show that error growth from a localized amplitude error within a North-Atlantic ridge to the large-scale error pattern associated with the breaking wave is dominated by (quasi-)barotropic dynamics. This result suggests that convectional error growth models, in which localized, finite-amplitude errors grow by baroclinic instability, need to be extended by a nonlinear component reflecting barotropic growth.

Decomposition of advective tendencies can be used to analyze individual contributions to the evolution of forecast errors. Panels a), b), c) show the contribution attributable to quasi-barotropic dynamics (Rossby wave propagation), the divergent flow, and baroclinic interaction, respectively, to the material tendency of PV forecast errors on 320K (shaded, in PVU/s, note the different scales of the color bars) over the North Atlantic for a 48h forecast (initialized on 00UTC 11 December 2013 ). The tendencies are calculated from the adiabatic version of Eq.6 in Davies and Didone (2013) using the decomposition of the advective tendencies from work by Franziska Gierth. For reference, the solid (dashed) contour depicts the PV = 2PVU isoline in the analysis (forecast).   The ``barotropic'' and the divergent component make prominent contributions to the amplification of the ridge error. The baroclinic component is subordinate and generally an order of magnitude smaller.