Vacillations Due to Wave Interference: Applications to the Atmosphere and to Annulus Experiments

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Abstract
It is noted that vacillations in zonally averaged flows can arise from wave interference between coexisting waves with the same zonal wavenumber but different phase speeds. We show that the appropriate baroclinic instability problem for the annulus does yield multiple instabilities which can produce vacillations via interference. It is also shown that the interference of travelling Rossby Waves with stationary forced waves can lead to vacillations whose amplitudes and periods are consistent with the observed index cycle.