Research brief: What drives extreme heat events in spring?

Picture: Spring sun. Credit: Hrvoje Abraham-Milićević (Pexels).

Maximum temperatures in Australia during spring have exceeded historic records on multiple occasions in recent years. Understanding what drives these high temperatures may lead to better forecasts of extreme heat in the future.

In this study, we looked at three extreme heat events, September 2013, October-November 2014, and October 2015, in reanalysis and in a seasonal prediction model. We compared the atmospheric circulation during each of the events to find circulation features that could help us understand how the heat formed.

Cyclonic circulation southwest of Australia and an atmospheric wave train with anticyclonic circulation over southern Australia were important features in these events. While the Indian Ocean Dipole was not active, the wave train appeared to come from the tropical Indian Ocean and was particularly important in the second two events.

The model ensemble members that forecast the highest Australian maximum temperatures also best forecast these atmospheric circulation features. However, the model over-represented the relationship with the Pacific Ocean at the cost of the relationship with the Indian Ocean. This poor relationship may mean that the model might underestimate future extreme spring heat events, a factor that should be assessed in future seasonal prediction models.

• Paper: McKay, R.C., Arblaster, J.M., Hope, P. et al. Exploring atmospheric circulation leading to three anomalous Australian spring heat events. Clim Dyn (2021). https://doi.org/10.1007/s00382-020-05580-0.