Picture (above): Antarctica. Credit: Yuriy Rzhemovskiy (Unsplash).

Weather systems in the southern Indian Ocean are important for delivering rainfall to key agricultural and population regions in southern Australia, as well as snowfall to East Antarctica.

If we investigate the variability of these weather systems over monthly, seasonal or annual timescales the pattern often looks like a doughnut. The hole of the doughnut represents Antarctica, and the ring of the doughnut is the westerly winds over the Southern Ocean that revolve around this icy continent.

In climate science, the expansion and contraction of the westerly wind belt (i.e. doughnut ring) around Antarctica is referred to as the Southern Annular Mode, or SAM. But on a daily timescale, the weather systems that influence the rainfall, temperature and wind conditions that we experience do not look anything like a doughnut.

By grouping weather systems by similar patterns rather than averaging conditions over months, seasons or years, CLEX researchers found that between Australia and Antarctica, the ‘doughnut’ structure of SAM is split into multiple ‘flavours’ and is more likely to have ‘bite marks’ out of it than be a perfect ring. These different flavours of SAM mean a hemispheric index often fails to capture the regional variability in surface weather conditions over southern Australia and East Antarctica.

  • Paper: Udy, D. G., T. R. Vance, A. S. Kiem, N. J. Holbrook, and M. A. J. Curran, Links between large-scale modes of climate variability and synoptic weather patterns in the southern Indian Ocean. J. Climate, doi: https://doi.org/10.1175/JCLI-D-20-0297.1.