Quasi-resonant amplification

Quasi-resonant amplification is a proposed mechanism in atmospheric dynamics in which the natural frequencies of Rossby waves in the zonal flow constructively interfere with the frequency of thermal forcing — such as land-sea temperature contrasts or orographic heating — producing wave amplitudes far larger than either forcing alone would generate. This resonance is quasi because the zonal flow is never perfectly steady; the waves and the flow co-evolve, and the resonance condition is met only intermittently.

The concept was developed to explain why some atmospheric blocking events achieve extreme amplitude and persistence while others dissipate quickly. It connects the microphysics of wave-mean flow interaction to the macro-scale pattern of mid-latitude weather extremes, suggesting that the atmosphere has preferred modes of organization that are not fixed attractors but temporary resonant states. Whether quasi-resonant amplification is increasing in frequency under climate change remains an open question with profound implications for predictability.