August 17, 2020 | Published by |

Picture: Windswept wave on the Gold Coast. Credit: Marianne Heino (Unsplash).

At a time when so much of the news has been grim, we have been delighted with continuous good news from our students over the past four months as they hit milestones and completed  PhD and Masters degrees. Since the last newsletter report Guillaume Liniger and Stephy Libera presented their PhD confirmation seminars; Taimoor Sohail passed his final PhD examination; Ram Patel submitted his PhD thesis; Sonja Neske and Matthius Zeller PhDs were officially awarded; and Alex Borowiak submitted his Masters thesis. We even saw a past student Serena Schroeter, who worked with many of us in ARCCSS, complete her PhD. Impressively, she achieved this while working fulltime for the Bureau of Meteorology and having twins. Serena is now working with Richard Matear at CSIRO on sea-ice modelling.

We were also pleased to see Bishak Gayen (University of Melbourne) and Shane Keating (UNSW) receive a Universitas 21 Global Education Fund award to develop online teaching resources in ocean, weather, and climate science.

Congratulations also go to Catia Domnigues who is part of the editing team that has produced a special issue for Springer journal Surveys in Geophysics: Relationships between coastal sea level and large-scale ocean circulation that has been turned into a hardcover book.

Amidst all these PhD completions and successes, our publication of important research has continued regardless of the pandemic. A large part of this research involved understanding and improving our ocean and climate models to disentangle how distant processes can affect climate and weather in Australia and around the world.

One of the regular themes that rises from our research is how small changes can have large impacts on chaotic systems. This was found to be the case in recent research where we looked at open ocean convection. This convection plays a key role in feeding a series of currents that together form a part of the global ocean ‘conveyor belt’. This conveyor belt, in turn, transports heat from the equator to the poles and keeps global temperatures relatively mild, which is why, open-ocean convection plays an important role in regulating our global climate. However, a large proportion of climate models often make this form of convection too strong. By comparing two models CLEX researchers found the current generation of convection parameterisations fail to replicate the random, chaotic nature of real-life turbulent convection. Therefore, surface waters sink too far compared to the real ocean. Our researchers have now proposed a convection parameterisation that recreates the random nature of turbulent convection, a challenge that will be undertaken in future research.

While it is often true that improving models involves a focus on small details and complex interactions, simplifying processes can also have profoundly important results. In one very interesting outcome, CLEX researchers found the inclusion of upper South Pacific Ocean variability in simple linear inverse models significantly improved predictions of ENSO and Pacific Decadal Oscillation. This result has implications for our capacity to improve forecasts of these events and predict their impacts on Australia further ahead, while using computer models that demand less time and computational expense.

As part of the process of investigating model improvements and their capacity to reproduce the Australian climate, our researchers also compared the capacity of the latest range of climate models that will be used in the next IPCC report, CMIP6, to earlier CMIP5 models. CMIP6 rainfall projections over Australia were similar to CMIP5, but the ensemble examined had a narrower range of rainfall change in austral summer in northern Australia and austral winter in southern Australia. Overall, future national projections are likely to be similar to previous versions but with some areas of improved confidence and clarity.

As we see improvements in our models, we also improve our ability to understand what causes some of the phenomena we observe in the real world. The warming of waters around Antarctica is an acknowledged observation but where the warm water was coming from and what this meant for future climate processes was something of a mystery. Using a high-resolution ocean model, CLEX researchers unexpectedly found 80% of the transport in the warm water layer, known as Circumpolar Deep Water, approached Antarctica in the colder regions. The most surprising result of the study was that warm regions of the Antarctic continental shelf actually have very limited warm water flow onto the shelf, compared with dense water formation sites. Instead, these regions are warm because the waters have been on the shelf for a long time and are subjected to minimal cooling from the atmosphere. These new results are forcing oceanographers to re-examine their understanding of the mechanisms that warm the Antarctic oceans.

Another observation that has challenged climate researchers is how between 2005-2015, the Southern Hemisphere oceans warmed faster than Northern Hemisphere oceans. This asymmetry contributed to a global warming hiatus from 2001 to 2012, and a range of theories have been put forward to explain it, from blaming atmospheric aerosols to the claim that the phenomenon contradicts climate change. PhD student Saurabh Rathore led research combining international datasets and climate models that showed the asymmetry between hemispheres can be explained by natural variability in the climate system superimposed on long-term ocean warming. This finding could help predict sea-level change or future temperature variations on a decadal time scale, something that is not achievable at the moment. It also shows with greater clarity that climate change is detectable in short records, whereas until now we have had to rely on longer trends of 20-50 years.

An examination of paleoclimate observations and climate model projections have also allowed strong conclusions to be drawn about how human-caused climate change is altering the Indian Ocean Dipole. All data sources agree that positive IOD events are becoming stronger and occur more often and that the mean-state of the Indian Ocean is moving towards a more positive IOD-like state due to enhanced warming in the west compared to the east. Palaeoclimate data further demonstrates that IOD variability even more extreme than recorded in recent decades is possible, and that IOD variability is important in long-term hydroclimate changes, including megadroughts.

Short term forecasting also got a boost when our researchers looked at the origin of rainfall during IOD and ENSO events and how this moisture moves through the atmosphere. To do this they analysed the variations in sea surface salinity that accompanied ENSO and IOD events. The researchers found clear rainfall-salinity relationships during these events. With this understanding, they performed a case study of the 2010/11 Brisbane floods. The researcher found the changes in sea surface salinity that brought the extreme rainfall to Brisbane were clearly detectable before ENSO and IOD events peaked. This finding raises the prospect that tracking changes to sea surface salinity has the potential to improve forecasts of Australian rainfall.

While our important research continues to be published, we have also maintained our international and national research relationships even through the isolation forced on us by COVID19. Our research program has been actively involved in online meetings and workshops.

The COSIMA workshop continued this year online with a range of speakers including Annie Foppert, Andreas Klocker, Will Hobbs, Siobhan O’Farrell, Alberto Alberello, Alessandro Tofolli, and Isabela De Souza Cabral. You can find all of their COSIMA presentations online here

The Tropical Variability team also put together an ENSO video meeting, following an EGU format, with presenters Andrea Taschetto, Muhammad Adnan Abid, Antje Weisheimer, and Tobias Bayr. You can find these talks on the CLEX website, here. In all, it has been a demanding four months but, through resilience and initiative, we have been proud to see our team members and students forge ahead.