The influence of Southern Hemisphere sea-ice extent on the latitude of the mid-latitude jet stream

An atmospheric general circulation model with prescribed sea-ice and sea-surface temperatures is used to examine the sensitivity of the atmospheric circulation to changes in sea-ice extent in the Southern Hemisphere. Experiments are conducted where the sea-ice edge is expanded or contracted by 7 degrees of latitude compared with its position in a control run. The experiments suggest that the latitude of the sea-ice edge influences the latitude of the Southern Hemisphere mid-latitude jet stream, but that the amplitude of the atmospheric response depends critically on the location and seasonality of the sea-ice anomalies. During the cold season, the mid-latitude jet shifts significantly poleward when the sea-ice extent is increased, but exhibits very little response when the sea-ice extent is decreased. During the warm season, the jet does not shift significantly regardless of whether the sea-ice edge is extended or contracted. The cause of the asymmetry in the atmospheric response relates to the extent to which the sea-ice anomalies affect meridional temperature gradients in the near-surface baroclinic zone. The results suggest that 1) any future decreases in Antarctic sea-ice are unlikely to have a profound effect on the Southern Hemisphere mid-latitude circulation; and 2) the usefulness of sea-ice variability for seasonal prediction is limited to the cold season and to the case of increases in sea-ice extent.