The blocking of middle latitude westerly winds by planetary waves

Abstract

Abstract A study of hemispheric data suggests that the splitting of westerly winds by blocking anticyclones is initially due to simple interference between stationary planetary waves with very large amplitudes but normal phases. A simple model is then used to investigate Green's hypothesis that the blocking anticyclone, once formed, can be maintained by baroclinic waves travelling in the split jet. The results are in good agreement with observations, particularly the vertical structure. A resonance seems likely at zonal wavenumber four.