Abstract
Abstract The structure of eddies forcing the vacillation of the southern midlatitude tropospheric zonal-mean zonal wind and the significance of wave–mean flow feedbacks on its persistence are assessed using a 100-yr 8-h dataset simulated by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mark 2 general circulation model. Using time-lagged regression and composite analyses relative to the vacillation index, it is shown that high-frequency (HF) eddy momentum flux anomalies near the mean jet latitude provide much of the forcing of the zonal-mean anomalies, as in observations. Low-frequency (LF) eddies also contribute, while the cross-frequency flux enhances short-term variation of the index. The HF band also provides a positive feedback, which is partly countered by an LF negative feedback. High- and low-index composites of representative midtropospheric waves (zonal wavenumbers 7 for HF and 3 for LF) are constructed, including those for waves phase shifted relative to the wave at th...
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