How to diagnose Rossby wave resonance along a circumglobal jetstream?

Some time ago, resonant amplification of Rossby waves along a circumglobal jetstream was hypothesized as the underlying reason for extreme weather in observed episodes. The argument is based on refractive index theory in the framework of the linear barotropic model. This theory allows one to diagnose the existence of a zonal waveguide - and, hence, the possibility of Rossby wave resonance - by a straightforward analysis of the meridional profile of the basic state zonal wind. The current paper contrasts the results from this theory with a recently developed method that makes less assumptions and approximations and is, hence, considered as benchmark. Comparison between the two methods shows that refractive index theory gives results that are both qualitatively and quantitatively inconsistent with the benchmark method. Experiments with idealized jets allow one to understand the shortcomings of refractive index theory. It is concluded that refractive index theory is fundamentally inappropriate as a diagnostic for Rossby wave resonance.