Planetary waves on the beta plane
Rossby waves are large-scale oscillations in the atmosphere and ocean caused by the variation of the Coriolis force with latitude (the β-effect). On a beta plane, where f = f₀ + βy, these waves propagate information about changes in vorticity across planetary scales.
Key insight: Phase velocity is always westward, but group velocity (energy propagation) can be eastward for short waves (large k). This explains why weather systems and ocean eddies tend to propagate westward, while the energy from localized disturbances can spread in both directions.