Heatwaves are prolonged periods of excessive heat, driven by various physical mechanisms. We know that one important mechanism that drives heatwaves over Australia is the El Niño-Southern Oscillation (ENSO). Previous work has categorised the significance of the relationship between heatwaves and ENSO, however an investigation on how ENSO drives Australian heatwaves is lacking. CLEX researchers attempted to fill this gap.
By employing an atmosphere-only version of ACCESS, they generated multiple sea surface temperature patterns of the same El Niño and La Niña events to assess how this influenced heatwaves over various Australian regions. A trajectory analysis was also employed to determine where the air during heatwaves comes from, and how this differs between heatwaves during El Niño and La Niña phases.
They found the length and frequency of heatwaves in northern and northeast Australia are affected by ENSO through the land surface, the state of soil moisture when heatwaves occur, and changes in the surface energy balance. The importance of how the atmosphere and land interacts during ENSO related heatwaves may explain why some El Niños have few heatwaves over these regions. This finding may help improve the seasonal prediction of heatwaves over these parts of Australia.
Over southern regions of Australia the influence of ENSO on heatwaves was weaker, but any effect may have manifested from the movement of heat towards the area experiencing a heatwave, and also the movement of warm air from the upper to lower atmosphere. In line with previous research, the researchers found that south-eastern heatwaves received little influence from ENSO.
Paper: Loughran, T.F., A.J. Pitman and S.E. Perkins-Kirkpatrick, The El Niño-Southern Oscillation’s effect on summer heatwave development mechanisms in Australia, Climate Dynamics, (2018). http://link.springer.com/article/10.1007/s00382-018-4511-x