Rossby wave dispersion relation on the beta-plane: ω = U₀k − βk/(k²+l²). The phase speed c = ω/k = U₀ − β/(k²+l²) is always westward relative to the mean flow. Color shows the stream function perturbation ψ; arrows (visible at low zoom) show the horizontal wind. Rossby waves are responsible for the large-scale meanders in the jet stream and blocking events.