Antarctica plays a crucial role in the Earth’s climate system by reflecting solar radiation back into space. The large white ice surfaces and clouds play a decisive role in this process. However, how clouds actually form in Antarctica, how they interact with the atmosphere and what role aerosols play in this process has not been sufficiently researched to date. Engaging in the SANAT flight campaign, the Alfred Wegener Institute, the Leibniz Institute for Tropospheric Research and the Max Planck Institute for Chemistry aim to help close this knowledge gap. The flight-based aerosol measurements conducted in Antarctica are the first of their kind in 20 years and also the first to extend deep into the interior.
Clouds form when water vapour condenses on tiny particles in the atmosphere, known as aerosols. These can be particles of sea salt, dust, soot or other materials on which water droplets or ice crystals form. There are significantly fewer aerosols in the atmosphere above Antarctica, however, than in most other regions of the Earth. If their frequency and composition change, this can have a correspondingly major influence on cloud formation and thus also on the planet’s ability to reflect the solar radiation into space.
Exactly how aerosols and clouds interact with each other in Antarctica, however, is not yet fully understood. “In order to close this knowledge gap, we are investigating the natural and anthropogenic sources of aerosols, the conditions under which new particles form, and how their properties change when they float at different altitudes in the atmosphere or are transported over oceans, ice shelves and the Antarctic continent,” as Dr Zsófia Jurányi from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) outlines.
Teaming up with Dr Frank Stratmann from the Leibniz Institute for Tropospheric Research (TROPOS) and Prof. Stephan Borrmann from the Max Planck Institute for Chemistry (MPIC), the AWI physicist is heading the SANAT (Spatial distribution of ANtarctic Aerosol and Trace gases) flight campaign, in which the consortium is investigating the most important sources and transport routes of aerosols in the Antarctic atmosphere. “We are particularly interested in particles that act as condensation nuclei or ice nuclei, as these ultimately lead to the formation of liquid phase, mixed phase or ice clouds.”
To this end, the SANAT team collected extensive data in January and February on board the AWI research aircraft Polar 6. Under challenging Antarctic conditions, researchers flew ten measurement flights from the German Neumayer Station III to the southern 80th parallel. “The last comparable measurements took place 20 years ago, and the campaign at that time focused only on the spatial distribution of aerosols in the Antarctic coastal region,” says Dr Frank Stratmann from TROPOS. “We have now measured aerosols far to the south over the Antarctic Plateau for the first time, in some cases using techniques and methods that have been newly developed.”
The “T-Bird” is one of these instruments: the towed probe is pulled behind the aircraft on a 60-metre-long cable and collects data independently. Together with simultaneous measurements on board the Polar 6 and ground-based measurements at Neumayer Station III, the researchers were able to gather comprehensive information on the frequency, small-scale transport processes and chemical composition of aerosols in the atmosphere, as well as meteorological variables such as air pressure, temperature and water vapour content. In the course of their flights, they were able to collect extensive data, which they are now aiming to evaluate over the coming months. An initial assessment has already revealed something surprising: “In the interior, we observed an unexpectedly high aerosol concentration as well as interesting chemical compositions,” reports Prof. Stephan Borrmann from the MPIC.
“Antarctica and its surroundings are crucial components of the global Earth and climate system, which react to climate change and its effects, while also influencing them at the same time,” as Zsófia Jurányi explains. “With this unique data, our campaign not only helps to improve weather forecasts and climate simulations. We are also contributing to a better understanding of the interaction of clouds with aerosols and assessing their influence on future climate conditions.”
The Polar 6 is one of two polar aircraft the AWI uses to study atmospheric processes, sea ice, snow and other geological and glaciological structures on Earth. The flying research laboratory is especially equipped for scientific expeditions in the Arctic and Antarctic. The two Basler BT-67 Polar 5 and Polar 6 aircraft have been in worldwide service since 2007. The measuring instruments at work inside and outside the aircraft are reassembled and recalibrated for each mission and enable AWI polar aviators to explore areas that are otherwise difficult to access.
The current aircraft measurements build on earlier DFG projects with ground-based direct measurements and ground-based remote sensing, which provided initial insights into cloud formation in the vicinity of Neumayer III: since 2019, cloud condensation nuclei (CCN) and ice nuclei (INP) have been measured in situ at the trace observatory. In 2023/24, TROPOS spent a year studying the clouds above Neumayer Station III using lidar and radar with a container that was especially transported to Antarctica. Both projects contributed to expanding the measurement programme at Neumayer Station III in the clouds area, in order to learn more about the special features of Antarctic clouds.
