Southern Hemisphere winter cyclone activity under recent and future climate conditions in multi-model AOGCM simulations

This article investigates extratropical winter cyclone activity in the Southern Hemisphere (SH) in a multimodel ensemble (MME) of coupled atmosphere-ocean general circulation model (AOGCM) simulations of recent and potential future climate conditions. Most individual models and also the ensemble mean yield good reproductions of the typical cyclone characteristics found in reanalysis data, although some individual models show peculiarities, and a large inter-model spread in terms of quantity of identified cyclone tracks is found. We use a scaling approach to combine the cyclone statistics from different models into a MME. In the future climate simulations, the total number of SH cyclones is reduced, whereas an increased number of strong cyclones is found in most models and in the ensemble mean. The long term trend with respect to all cyclones is a robust feature throughout the simulations. It is associated with a general poleward shift, shown to be related to both tropical upper tropospheric warming and shifting meridional sea surface temperature gradients in the Southern Ocean. The magnitude of increased strong cyclone activity has a focus on the Eastern Hemisphere. It is clearly influenced by natural variability and thus depends on specific time periods considered.