December 3, 2018 | Published by | ,

The Heatwaves and Cold Air Outbreaks Research program has been very active, producing a considerable number of papers over the past four months, including more groundbreaking work in the relatively new research area of marine heatwaves.

There were also individual successes, with Associate Investigator Markus Donat highlighted in an article on early career scientists by the International Association of Meteorology and Atmosphere Sciences. Markus has now relocated from the University of New South Wales to Barcelona but will continue to be a part of the program.

Closer to home, researchers have long known the seas to the south and east of Tasmania are one of the fastest warming ocean areas in the world. Marine heatwaves have become a familiar feature in this area but understanding their fluctuations has been elusive.

Using observations over a 24-year period, Centre researchers teased out the causes and characteristics of these heatwaves. They highlighted the role and interactions of the East Australian Current (EAC) and the Zeehan Current (an extension of Western Australia’s Leeuwin Current) in determining the strength of marine heatwaves in this region.

The researchers revealed that an unusually strong EAC extension leads to an increase in the probability of marine heatwave days. Conversely, a strong Zeehan Current during these seasons decreased the probability of marine heatwave days. This is work that will help improve our ability to forecast these events and understand their impact on marine ecosystems.

CLEX researchers also examined the role of human caused climate change in marine heatwaves globally as part of the Bulletin of American Meteorological Supplement, highlighting two case studies – the Great Barrier Reef heatwave of 2016 and an Alaskan marine heatwave in the same year. The researchers concluded these specific events were 50 times more likely as a result of climate change.

Back on land, Centre researchers looked at the atmospheric conditions that produce heatwaves over Brisbane. There is a general assumption that heatwaves are caused by the location of a high-pressure system over a region. However, this research found that a low-pressure system just off the southeast corner of Australia could also cause heatwaves in Brisbane.

This research suggests that when we examine how heatwaves may change in the future, we not only have to look at how high pressure systems may change but that the location, intensity and variability of mid-latitude storm tracks will also play a role.

In looking at how models represent our changing climate, CLEX tackled another tough problem. It is unclear if models accurately capture the amplification of heatwaves during hot and dry conditions in what are normally wet regions. Using observations and data from flux towers across Australia our researchers compared the outputs of climate models with observations for hot and dry periods in these regions. They found models overestimated the interaction between hot and dry days in wet regions, over-amplifying heat extremes. This has opened the way for further model and forecasting improvements.

Another area where models struggle is in understanding the trends in sea ice volumes around Antarctica. CLEX researchers from the heatwaves and cold air outbreaks, and the climate variability and teleconnections programs, analysed 10 models to see if this could be improved. They aimed to determine how dynamic processes – like sea ice motion – and thermodynamic processes – such as freezing and melting – influenced model outputs of sea-ice volumes around Antarctica.

As a result of the work, it was considered likely that dynamic processes may play a more important role than freezing and melting processes. Therefore most climate models may overestimate the role of thermodynamic processes. As this was one of the first studies of ice volume, it was not clear of the relationship between this and trends in ice area.

The Heatwaves and Cold Air Outbreaks Research Program organised and hosted a workshop that brought researchers from across Australia and around the world to examine and also to look at the effectiveness of detection in attribution for heatwaves and some extreme rainfall events. Michael Werner from Lawrence Berkeley National Lab (US) an expert in attribution studies of rain events was not only a guest at this workshop but also spent some time with CLEX researchers as a visitor.

The third day of the workshop had a strong communication focus, bringing in four media professionals – Anja Taylor (ABC Catalyst), Wendy Frew (BBC, Sydney Morning Herald, ABC), Tom Arup (The Age) and Michael Lucy (Cosmos Magazine). Together with climate researchers they aimed to work through the best way to deliver information on extreme events to news organisations and the general public.