December 7, 2019 | Published by | , ,

Picture (above): Puddle jumping. Credit: Neonbrand (Unsplash).

Sometimes there is so much to look back on that it can be difficult to know where to begin and that is definitely the case for the past three months of a very active Extreme Rainfall research program. But as an old teacher once said, when in doubt it pays to go back to basics and as far as climate research goes there are few things more fundamental than observations and datasets.

In 2016, researchers who are now part of CLEX, were involved in a voyage on the RV Investigator as part of the Clouds, Aerosols, Precipitation, Radiation and Atmospheric Composition Over the Southern Ocean (CAPRICORN) experiment, which took in situ measurements of a range of important climate metrics. These measurements have now been used by Extreme Rainfall researchers to identify the accuracy of key datasets for the Southern Ocean used by the international climate community in climate models. While some small biases were uncovered, in general the datasets appeared to be fairly robust.

Our researchers then used these same measurements to determine the accuracy of observations retrieved by the Japanese geostationary satellite, Himawari-8. This satellite provides useful data on clouds for our region at relatively high resolution. For this reason researchers need to know if it produced any biases, particularly around cloud-top height and cloud-top temperature, whose roles are critical in shaping Earth’s climate. The majority of results agreed reasonably well with both the shipborne and CALIOP satellite estimates. However, some major systematic biases are also identified.

The power of improving our observations can be seen in a recent paper that focused on convection and the tropical monsoon and how this affects annual rainfall over Australia and Africa. Climate models do not reproduce the changes in this region very well, so observations of clouds and rainfall are vital in helping us understand the processes. CLEX researchers found large-scale monsoon circulation suppressed rainfall in some areas and even shifted important high-top clouds away from areas of convection that may otherwise have produced rain. These insights highlighted factors that lead to poor model performance for this region, opening the way to future improvements.

But that doesn’t mean models aren’t useful for helping us understand rainfall patterns across the maritime continent and down into tropical Australia. By using a simplified model CLEX researchers were able to tease out the relationship between rainfall and the thermal structure of the atmosphere in the tropics. They found a clear relationship between humidity, precipitation and a high contrast between temperatures at different atmospheric heights. This revealed new atmospheric interactions that helped explain some of the issues climate models have for this region.

This combination of improving observations and better understanding the processes that inform climate models came together in a practical way through a paper that looked at how tropical cyclones may change for our neighbours to the north in the Philippines. The climate models found that as the Earth warms, the Philippines would experience fewer but more intense cyclones. For a region that has recently borne the brunt of some of the strongest cyclones ever recorded, this was valuable news for a country that will need to adapt to the future impacts of climate change.

Closer to home, 13 years of Darwin radar measurements of cloud structures revealed the contrast in conditions that can lead to powerful localized storms that may lead to flash flooding events or widespread soaking rains. While giving insight into these differing convective events it also highlighted the value of Australia’s radar network to climate scientists and how it helps science and can improve our models.

A combination of a high resolution weather model – the kind that is informed by radar observations – and aircraft measurements allowed CLEX researchers to explore a severe aircraft turbulence event even though the plane was 50km away from a convective system. The researchers demonstrated this unusual case could be explained by a large amplitude atmospheric gravity wave that was generated by storm, which then amplified and ‘broke’ in the region of the turbulence encounter. This case offers further evidence of the importance of gravity waves as a source of turbulence and highlights inadequacies in current turbulence avoidance guidelines.

When it comes to climate models few are more important than Australia’s ACCESS model. So the Extreme Rainfall program was delighted when Prof Christian Jakob was named as a member of the ACCESS Oversight Committee. This committee aims to provide a forum to share information, raise issues around ACCESS development and improve coordination around ACCESS making it an important player in the Australian climate community.

Along with climate models, convergence is of critical importance for extreme rainfall. To demonstrate this almost 40 members of the extreme rainfall program converged on The University of Melbourne Earth Sciences building on September 23 for our second program-wide workshop. The workshop featured 16 talks, organized into our four sub-questions, each generating a great deal of discussion and ideas for future research and collaboration. As usual, the excellent Melbourne weather and coffee left our interstate visitors envious.

Meanwhile, the influence of our researchers continues internationally. Chief Investigator Lisa Alexander will be a guest editor on Compound Weather and Climate Events a special issue of the journal Weather and Climate Extremes. Associate Investigator Yi Huang will also be guest editing a special edition of Atmosphere, Observations and Simulations of Clouds, Aerosols, Precipitation, and Radiation over the Southern Ocean.

We were also visited for four weeks by the Director of NASA GISS, Gavin Schmidt, where he collaborated with Steve Sherwood, held two seminars and put on a special 3-day workshop on science communication.

We have also travelled to visit our international partners. In August Todd Lane travelled to NCAR as part of a collaborative visit. You can find out more about that trip here.

There is also a host of congratulations. Students Amy Hewitson and Terence Hewitson submitted their honours theses; Scott Clark was awarded his PhD for his work in rainfall regimes in north-western Australia in observations and climate models and RP co-leader Todd Lane was made a professor.

Finally, we can’t fail to mention the great outreach activity by students Kim Reid and Alex Borowiak who were guest climate researchers as part of an immersive art installation, Plastisphere, at Coburg Carnivale on September 20-21. You can read more about this experience with Kim’s blog on the CLEX website, Enter the Plastisphere.