Abstract

Variability of the large-scale mid-latitude Southern Hemisphere circulation is dominated by apparently random wanderings of the mid-latitude jet. These wanderings of the jet have an important influence on a variety of components of the Southern Hemisphere climate system, including the location of synoptic storms and Antarctic sea-ice extent. For example, the unprecedented retreat of Antarctic sea-ice that occurred during the spring of 2016 has been linked to unusual behaviour of the jet and increased synoptic storm activity.

In this talk several lines of evidence will be presented to argue that variations of the Southern Hemisphere mid-latitude jet are more systematic than previously thought. In particular, it will be argued that jet variability during austral spring and summer is closely coupled to the seasonal cycle of the polar vortex in the stratosphere. Based on this connection with the seasonal cycle of the stratospheric circulation, an alternative perspective of tropospheric jet variability will be proposed. This alternative perspective will subsequently be used to re-interpret several previous results in the literature, and also to motivate a partial explanation for the unprecedented Antarctic sea-ice behaviour during spring 2016.