Stationary Planetary Waves, Blocking, and Interannual Variability

Abstract

This chapter describes the various aspects of stationary planetary waves, blocking, and interannual variability. The trends in the study of large-scale planetary waves and their anomalies are presented. The intensity of activity on the topic stems from the belief that the anomalies can be unusually long lived and may represent particularly predictable features of weather. It is found that while the bulk of planetary-wave anomalies are not persistent in a physically meaningful way, there is in fact some significant interannual variability in stationary waves. The existence of resonance is crucially dependent on the mean zonal wind. It is found that in each model, stresses due to the resonant stationary wave play a major role in determining the mean flow. Resonances arise from the repeated reflection of waves from such surfaces where incident and reflected waves are in phase so that amplification may take place. In idealized models the reflecting surface is perfectly horizontal and the necessary constructive interference is readily achieved. The linearized response to stationary forcing is also elaborated.