Rossby-wave downstream development

A wave packet can transfer energy downstream faster than individual phase features move, allowing successive downstream disturbances to develop while upstream ones weaken. In the simple uniform-current barotropic model with zero meridional wavenumber, the zonal group speed is $U+\beta /k^2$ while phase speed is $U-\beta /k^2$. Linear superposition and interference are not direct nonlinear eddy scattering. Real weather development also involves baroclinic energy conversion and wave–mean-flow feedback, which require additional dynamics.