The climate of the Southern Hemisphere has undergone significant changes over the past 30-50 years. The westerly winds over the Southern Ocean have seen a shift poleward towards Antarctica, particularly in austral summer, drawing the rainfall systems along with it. While the influence of anthropogenic forcing such as ozone depletion and increasing greenhouse gases on these changes is well-established, a significant contribution from tropical variability to these trends has recently been identified. The importance of tropical to extratropical interactions in shaping other recent events is also becoming more evident. Examples include the deepening of the Amundsen Sea Low which has been associated with tropical Pacific variability and the rapid decline in Antarctic sea ice in 2016 which was linked to a record positive Indian Ocean Dipole event. In the opposite direction, the Antarctic polar vortex weakening in 2019 has been linked to the hot and dry conditions preceding the Australian bushfires that spring and summer. This talk will provide an overview of Southern Hemisphere tropical to extratropical interactions, their links to observed changes on interannual to interdecadal timescales and their relevance for future projections.

Tropical to extratropical interactions in the Southern Hemisphere