Recent modelling work by Scott & Haynes has shown that there is an internal biennial mode of interannual variability in the extratropical stratosphere in the absence of the QBO, due to interaction between extratropical planetary waves and the subtropical flow. The work to be described investigates implications of this mode for the extratropical response to equatorial QBO-like oscillations of varying period, e.g. is there an enhanced response when the tropical QBO-like oscillation has period two years, as opposed to other periods. We use a primitive equation, stratospheric, spherical geometry, mechanistic, spectral model, with only the zonally symmetric and zonal wave number one components resolved, to allow many multi-year simulations to be run. The work also reveals other aspects of two-way interaction between the annually varying extratropical planetary waves and (a parameterised) equatorial QBO, e.g. the effect of planetary wave driven upwelling on the QBO and the contribution of annual variations in the upwelling to irregularity of the tropical QBO.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics