August 13, 2021 | Published by | , ,

The Weather and Climate Interactions Research Program is now bedded down, and work is beginning apace. We now have fortnightly meetings on the second and fourth Tuesday of each month.

We have also started to see our researchers bring their expertise to a range of stakeholders, peer networks, and the broader community. Andrea Taschetto spoke at The Forewarned is Forearmed (FWFA) Project Webinar Series on ENSO diversity and Australian rainfall variability, which included an audience of farmers and agricultural stakeholders. Meanwhile, Christian Jakob, along with Andy Pitman, briefed Australian Senator Janet Rice on the details of the Centre’s briefing note, How might Australia contribute to a next-generation global climate modelling facility? 

There have also been public events. Linden Ashcroft spoke to 20 people as part of a webinar for Mornington Peninsula Council, Climate Change – What is it and what can we do about it? Katrin Meissner presented a talk, The climate has always changed – so why are we concerned now? at the joint meeting of mining geologist groups, SMEDG/AIG/GSA. Todd Lane was a panellist for the Building Resilience session at Melbourne Climate Futures – Climate 2021 public event. He also reached out to our peer networks, giving a guest lecture at the Department of Atmospheric Sciences, University of Hawaii.

While these developments are pleasing, COVID is having an impact, particularly when it comes to bringing in students and new postdocs into the program. That said, we were able to welcome two new PhD students. The first is Andrew Brown whose research is focused on severe thunderstorms in Australia, and how these events may change in a future climate. The second is Qinuo Huang who is investigating boundary layer dynamics during heatwaves. We also welcomed back Phuong Loan Nguyen who returned from Vietnam where she was stuck for a year as international travel ground to a halt.

Despite these challenges, we are already seeing a range of new research outcomes that are producing some fascinating results. Perhaps the most spectacular of our recent publications, certainly in terms of technology, would be the work Stacey Hitchcock performed with the Colorado State University Convective CLoud Outflows and UpDrafts Experiment. The Experiment aimed to enhance our understanding of deep convective storm processes and how they are represented in numerical models. To do this, the researchers ran an observational field campaign that included a “flying curtain” strategy, where that curtain was made up of a fleet of drones flying into a storm, high-frequency radiosondes that penetrated the clouds, and ground-based radar. Together these allowed the researchers to obtain detailed measurements of the area of cold pools and how long they lasted, along with updraft velocities. The result was extensive datasets from 23 storms. These datasets have since been used to test how well high-resolution climate models represent the processes that lead to cold pools produced by storms. The answer was quite well indeed.

Another study examining convective updrafts, this time in tropical climates, used radar observations taken from a wind profiler radar pair at Darwin. The convection that produces cumulus clouds in tropical storms is typically thought of as being made up of long continuous plumes of warm rising air, rather than shorter, incoherent plumes of around only 1km in vertical extent. Global climate models tend to parameterise cumulus convection in the first form, but detailed numerical simulations and aircraft observations tend to support the latter for typical warm-season convection. The results showed most updrafts were less than 2 km in vertical extent. They also identified that the updraft length increased with rain rates. With extreme rain rates, the average updraft lengths were around 5km, supporting numerical models.

While updrafts and cold pools can influence the development of storm systems at a local level, larger events higher in the atmosphere have also been found to affect our weather in a way that is very predictable. An example of this is sudden stratospheric warming events. Sudden stratospheric warming in the Southern Hemisphere are far rarer than those in the Northern Hemisphere but when they occur they impact the winds circling Antarctica, known as the polar vortex. This impact can shift the vortex off its centre or even split the vortex into two smaller vortices. Recent studies have debated whether these two types of sudden stratospheric warming have differing near-surface impacts. Our researchers found that over seasonal time ranges the difference was negligible but in the two weeks after a split event, there was a strong response in weather systems that would be useful for weather prediction.

CLEX researchers then wanted to know if these rare events would occur more frequently as the Earth warmed. Our researchers used a detailed climate model that reproduced the climate system over a period of 9,900 years. The results were stark. Under current conditions, the model estimated sudden stratospheric warming events would occur around once every 22 years. But in a warmer world, they almost disappeared occurring on average once in 300 years.

Another difference between northern and southern hemisphere climates is the greater brightness of clouds over the Southern Ocean, which reflect more sunlight back into space. Clouds remain one of the biggest sources of uncertainty in understanding how the Earth’s climate will change due to global warming. Clouds over the Southern Ocean are even more poorly understood due to sparse field observations, strong winds and storms and a pristine environment. Using observations taken from 20 research flights over the Southern Ocean we found supercooled liquid in the clouds explained their brightness. This supercooled liquid created new ice particles without needing a nucleus made of dust or pollution. Understanding this process can help improve the representation and modelling of clouds above the Southern Ocean, which continues to be an important challenge because of the impact these clouds have on global warming.

Another intriguing aspect of the Southern Ocean is that it is warming more slowly than many other ocean basins around the world. The question is will this slow rate of warming persist as climate change takes hold? Using a suite of coupled climate models the researchers found there would be a marked difference in warming depending on how we respond to carbon emissions. They found the level of warming under the high emission scenario is almost double that under the medium-low emission scenario.

Another major influence on the climate of Australia and the world is the El Niño Southern Oscillation. We know it influences many countries around the Pacific and even around the Indian Ocean, but CLEX research has also identified ENSO has a powerful connection to the Atlantic Ocean as well. Although this connection was not straightforward, with the link to the North Atlantic sea-surface temperatures being nonlinear with respect to the strength of the sea-surface temperature forcing in the tropical Pacific. For example, further increases in El Nino magnitudes ceases to create further increases of the tropical North Atlantic sea surface temperature anomaly.  However, the tropical teleconnection pathway was more linear than the extratropical pathway.

Understanding these climate connections and future changes requires lengthy observations. In many places, these simply don’t exist. CLEX researchers Joelle Gergis and Linden Ashcroft are working hard to correct this, using pre-instrumental datasets to create some of the longest consistent observation records for Australia. The latest of these has led to the construction of the oldest daily historical climate dataset for Perth, southwestern Australia. It provides an extended record for analysing pre‐industrial climate variability and extremes for the region. This newly digitised record contains sub‐daily observations of temperature, barometric pressure, wind direction, and weather remarks, including rain days, from 1830 to 1875.

Beyond the research, we have been delighted with the successes of individual students and researchers. Nina Ridder has had an excellent few months being re-elected for the Young Earth System Scientists executive committee for the second year in the row and was also accepted as a member of the Interim Coordinating Committee (ICG) of the new WCRP Home Regional Information for Society (RifS).

Christian Jakob has been appointed as a member of the Science Review Group for the Met Office Hadley Centre Climate Programme. You can find out more about the group here. Finally, PhD Student Josue Martinez Moreno took a big step towards his future career when he submitted his thesis. The next phase of his career takes him to Brest, France where he will take on a new postdoc appointment. He is just the latest in a long line of CLEX PhDs who will become future leaders in the climate research space.