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. Key Points The impact of sea‐ice on the atmosphere is highly seasonal and non‐linear An increase in sea‐ice during the cold season causes a poleward shift of the jet Future decrease in sea‐ice is unlikely to impact on the large scale circulation