A case of two way reinforcement between mean flow and eddy anomalies: variability of the Southern Hemisphere winter split flow

The maintenance of the Southern Hemisphere (SH) winter monthly-mean split/non-split flow anomaly has been examined by two model diagnostics in this study. A stationary wave model simulation illustrates that the split/non-split jet is maintained by the anomalous vorticity flux. The anomalous heat flux acts to weaken the split flow, but its effects are overwhelmed by those of the vorticity flux. The model also shows that the anomalous tropical heating is not important for the maintenance of the split/non-split flow.

The organization of high-frequency eddies by the low-frequency split/non-split jet has been studied by a storm track model simulation. Two sets of linear runs of a linear GCM with random initial perturbations superimposed onto the split and non-split jet basic state respectively have been conducted to establish the statistics of the storm tracks. The modeled storm track anomalies that are caused by the split/non-split jet match the storm track anomalies that are associated with the split/non-split jet observed in the ECMWF reanalysis data, thus demonstrating that the low-frequency split/non-split jet does organize the high-frequency eddies. Our results establish that there is a two-way feedback between eddies and mean flow anomalies in the low frequency variability of the SH winter split jet.