Gerald "Jay" Mace
Recent research conducted by Dr Gerald Mace from the University of Utah and colleagues reveals how air masses passing over the Antarctic continent naturally boost cloud brightness through a complex chain of chemical and physical processes. This natural phenomenon may hold important clues for improving climate models and predicting future climate change.
Nature’s Cloud Factory
The Southern Ocean is one of the most remote and pristine regions on Earth, making it an ideal natural laboratory for studying how clouds formed before human industrial activity began altering Earth’s atmosphere. This vast expanse of water encircling Antarctica experiences some of the planet’s strongest winds and stormiest conditions, yet it’s the region’s clouds that have captured scientists’ attention.
These clouds play a crucial role in Earth’s climate by reflecting sunlight back to space, but climate models have struggled to accurately simulate their properties. Understanding the mismatch between models and observations has become increasingly urgent as scientists work to improve predictions of future climate change.
Dr Gerald Mace and an international team of researchers have been investigating an intriguing pattern: clouds near Antarctica’s coast tend to be brighter and more reflective than those further north over the open ocean. This brightness comes from having more numerous but smaller water droplets packed into the clouds – a property that makes them more effective at reflecting sunlight.
Following the Air’s Journey
To understand what creates these especially bright clouds, Dr Mace and his colleagues tracked air masses as they moved across the Antarctic continent and over the Southern Ocean. They combined multiple types of observations, including data from satellites, research ships, and atmospheric measurements, to build a comprehensive picture of how the clouds evolve.
The team’s analysis revealed that air masses which had recently spent time over the Antarctic ice sheets produced clouds with particularly high numbers of droplets. This effect was especially pronounced when the air had travelled over Antarctica’s high-altitude ice domes, where temperatures are extremely cold and the sun’s rays are intense during the summer months.
These conditions, the researchers surmised, create an ideal environment for forming new particles that can later serve as seeds for cloud droplets. When this particle-rich air descends from the Antarctic plateau and moves out over the ocean, it produces clouds with markedly different properties from those formed in air masses that haven’t passed over the continent.
The Chemistry Behind the Clouds
The process begins in the biologically productive waters near Antarctica’s coast, where tiny marine organisms flourish during the summer months. These organisms release a chemical called dimethyl sulphide (DMS) into the air – a process that has been occurring in Earth’s oceans for millions of years. When this DMS-rich air rises and passes over Antarctica’s ice sheets, it undergoes a remarkable transformation.
Research at Australia’s CSIRO research organisation has examined the complex chemistry involved in this process. This work shows that over the ice sheets, where there are very few existing particles in the air and intense sunlight during summer, chemical reactions convert the DMS into sulfuric acid vapour. This vapour can then form completely new particles through a process called nucleation, which eventually become the seeds for cloud droplets.
This natural particle formation process proves particularly efficient because the air over Antarctica’s ice sheets is exceptionally clean – any existing particles have usually been removed by precipitation before the air reaches the continent. The newly formed particles, therefore, have little competition as they grow large enough to serve as cloud condensation nuclei, the essential seeds around which cloud droplets form.
Read the entire story in Scientia here.
