Southern hemispheric large-scale circulation changes in two opposing storylines of future Antarctic climate change

The Southern Hemisphere (SH) stratospheric polar vortex (SPV) is a key dynamical component of the atmospheric circulation, exerting a strong influence on tropospheric circulation and near-surface climate through stratosphere–troposphere coupling. Despite its importance, the future evolution of the SH SPV remains highly uncertain, as projections depend sensitively on the magnitude and character of Antarctic climate change. To address this uncertainty, storyline approaches offer a physically plausible framework that explores contrasting Antarctic climate futures in a structured way, without collapsing distinct responses into an ensemble mean.

Building on the storyline framework of Williams et al. [1], this study investigates the influence of two opposing scenarios of Antarctic climate change on the large-scale circulation of the SH using the ICON (ICOsahedral Nonhydrostatic) atmospheric model. Two physically motivated future scenarios are considered: one characterised by strong Antarctic sea-ice loss combined with an earlier breakdown of the SH stratospheric polar vortex, and one featuring weaker sea-ice loss and a delayed vortex breakdown. These contrasting boundary conditions provide a controlled framework to assess how different Antarctic climate pathways can force distinct stratospheric and tropospheric circulation responses within a single model.

For each storyline, 30-year simulations are analysed for present-day (1985–2014) and end-of-century (2070–2099) conditions. The analysis focuses on changes in stratospheric variability and stratosphere–troposphere coupling, with particular attention to the frequency and near-surface impacts of SPV weakening and strengthening events, thereby assessing the circulation pathways through which contrasting Antarctic boundary conditions affect the SH larg-scale circulation within one model.

 

 [1] R. S. Williams et al., “Future Antarctic Climate: Storylines of Midlatitude Jet Strengthening and Shift Emergent from CMIP6,” Journal of Climate, vol. 37, no. 7, pp. 2157–2178, Apr. 2024, doi: 10.1175/JCLI-D-23-0122.1.