Extremely clean air near the ground, warm air influxes, and sulfate aerosol at higher altitudes — a research initiative has revealed new findings about clouds in Antarctica.
Leipzig/Bremerhaven. The research project from Leipzig has uncovered new information about clouds in Antarctica, characterized by extremely clean air at the surface, warmer air intrusions, and sulfate aerosols aloft. Over the course of 2023, from January to December, the vertical distribution of aerosol particles and clouds in the atmosphere above the German Neumayer Station III, operated by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), was explored from the ground for the first time. These height-resolved measurements marked a significant first for Queen Maud Land, the Antarctic region adjacent to the Atlantic Ocean, which spans an area greater than Greenland.
The data collection was conducted using the OCEANET-Atmosphere platform from the Leibniz Institute for Tropospheric Research (TROPOS). This platform previously demonstrated its reliability during a year-long drift in the Arctic aboard the RV Polarstern as part of the international MOSAiC expedition in 2019/2020. Throughout its operation in Antarctica over the 12-month period, the platform was monitored on-site by TROPOS scientist Martin Radenz. The initial findings have been published in the journal Bulletin of the American Meteorological Society (BAMS). This research was supported by funding from the German Research Foundation (DFG) and carried out in collaboration with the AWI.
The Antarctic continent and the surrounding Southern Ocean are crucial elements of the global climate system. Although Antarctica’s climate was seen as relatively stable over the last century, notable changes are now being documented. Climate models predict that the interior of Antarctica will warm by over 3 Kelvin, that sea ice cover will decrease by approximately 30 percent, and that precipitation will rise during the 21st century. However, these predictions come with significant uncertainties, and current global atmospheric circulation models struggle to accurately represent cloud coverage and radiative forcing over the Southern Ocean. This misrepresentation of clouds causes inaccurate estimations of thermal radiation and sea surface temperature, which are essential for assessing energy exchanges between the ocean and atmosphere. Moreover, to document environmental changes in areas like Antarctica, it is vital to have a comprehensive understanding of its current state.
Understanding cloud formation in Antarctica is crucial, as it occurs differently in the pristine air of the southern hemisphere compared to the northern hemisphere, where land surfaces are more prevalent. Another significant source of uncertainty is the movement of moisture and particles from mid-latitudes and subtropic regions towards the polar areas. The relatively flat terrain between the Weddell Sea and the South Pole may serve as a conduit for warm, humid air masses.
To further investigate clouds in Antarctica, remote-sensing devices, including an atmospheric lidar and a cloud radar, were added to the instrumentation at the German research station Neumayer III as part of the COALA project (Continuous Observations of Aerosol-Cloud Interactions in the Antarctic). The importance of this project has been notably recognized by the DFG’s priority program ‘Antarctic Research,’ which provided funding for this endeavor. The equipment was housed in the TROPOS OCEANET-Atmosphere container, which had previously drifted through the Arctic for a year during the AWI-led MOSAiC expedition. “The MOSAiC observations allowed us to demonstrate for the first time that the atmosphere over the North Pole is more polluted than previously believed. But what about Antarctica? We were fortunate to operate our OCEANET container there for a full year,” said Dr. Ronny Engelmann from TROPOS. At the start of 2023, OCEANET was set up just 300 meters south of the German Antarctic Neumayer Station III. OCEANET-Atmosphere is a self-sufficient, polar-tested, fully equipped 20-foot container housing advanced atmospheric monitoring instruments. It is the only single-container platform in the polar regions that combines multiwavelength lidar, cloud radar, microwave radiometer, and Doppler lidar to study clouds and aerosols, including turbulent air movements.
OCEANET received power from the research station, where the Leipzig-based researcher lived for a year to ensure that all devices operated continuously: Dr. Martin Radenz from TROPOS was part of the station’s core team. He was among 10 people who endured the winter darkness at Neumayer Station III. “Having the opportunity to spend a year in Antarctica with our small community, experiencing the breathtaking nature, snowstorms, and isolation was an extraordinary adventure,” recalled Martin Radenz. The green laser beam of the multiwavelength lidar that scanned the atmosphere above Neumayer Station III represented a novel approach for this part of Antarctica. A lidar, often referred to as “light radar,” emits short laser pulses into the atmosphere and captures the returning light with a specialized receiver. Data regarding the height, quantity, and type of suspended particles (aerosols) in the atmosphere can be derived from the travel time, intensity, and polarization of the backscattered signals. Prior to this, similar measurements using cloud radar and aerosol lidar had only been performed at McMurdo Station, located 3500 kilometers away on the opposite side of Antarctica, bordering the Pacific Ocean. Unlike Neumayer III, which is positioned on an ice shelf, the US McMurdo Station is constructed on rock. Researchers are eager to see how the data collected at Neumayer Station III over ice shelves will enhance understanding of cloud formation over Antarctica’s vast icy terrains. “It is particularly encouraging that following COALA, the AWI plans to permanently deploy similar remote sensing instruments at Neumayer Station III in collaboration with TROPOS. This will significantly contribute to monitoring short-lived climate components such as aerosols and clouds in Antarctica,” remarked Prof. Andreas Macke, Director of TROPOS and Head of the “Remote Sensing of Atmospheric Processes” department.
In January 2024, the OCEANET container was disassembled, transported to the edge of the ice shelf, and loaded onto the resupply vessel. The equipment arrived in Leipzig in March, marking the conclusion of the DFG COALA project, allowing researchers to assess the outcomes: “All devices functioned well and gathered valuable data. We are especially pleased with this because if a replacement part was needed during the polar night, it would have taken months to arrive. Our previous experience from the MOSAiC expedition three years ago in the Arctic proved invaluable. Nonetheless, maintaining the devices against storms and clearing snow almost daily was truly challenging,” shared Martin Radenz. For Radenz and his team, the effort was undoubtedly worthwhile, as the measurements yielded three new insights into the Antarctic’s response to climate change:
The atmosphere is pristine only near the surface
Insights from the lidar measurements revealed the number of particles present above this portion of Antarctica and their altitudes. The lower troposphere showed relatively clean conditions. In contrast, an unexpectedly high concentration of particles was detected between 9 km and 17 km in altitude (stratosphere). “The lidar-derived optical characteristics of the aerosols clearly indicate the presence of sulfate aerosols, primarily attributed to Volcanic eruptions have led to the presence of aerosols in the stratosphere since January 2023, likely linked to the Hunga Tonga-Hunga Ha’apai eruption that occurred in January 2022, according to Martin Radenz. Both the lasting volcanic dust observed over the South Pole and the smoke from forest fires in the North, which was first detected during the MOSAiC expedition in 2020, have caught researchers’ attention, as noted by Ronny Engelmann. Ground-based lidar measurements play a crucial role since volcanic aerosols over Antarctica have not been adequately observed from space before; notably, NASA’s CALIOP satellite lidar didn’t detect these aerosols in its standard products. The aerosols in the stratosphere can influence the formation of polar stratospheric clouds (PSCs), where complex chemical reactions occur that may contribute to the ozone layer depletion in polar areas.
Interaction Between Aerosols and Clouds in Shallow Mixed-Phase Clouds
The study revealed more aerosols in the upper atmosphere than anticipated, while lower layers were as clean as expected. Continuous measurements allowed researchers to “observe” cloud development over time. For instance, a stable mixed-phase cloud made of ice crystals and water droplets within a layer of marine aerosol was monitored for 10 hours. Dr. Patric Seifert from TROPOS explained, “Our findings demonstrate that nearly all particles act as cloud nuclei, facilitating the formation of cloud droplets or ice crystals. The growth of clouds is therefore restricted by the number of particles present. If more particles entered the Antarctic atmosphere, perhaps from more polluted air, there would be an increase in cloud droplets and ice crystals, potentially altering the clouds’ lifespan and impacting weather and climate in unknown ways.”
Unexpected Warm Air Intrusions
Warm air from lower latitudes may accelerate climate change in Antarctica, making it crucial to analyze two significant warm air intrusions. One intrusion in April brought intense snowfall, accounting for 10% of the yearly total, while another in July resulted in record high temperatures and severe icing due to supercooled drizzle. On July 6, 2023, temperatures at the German Antarctic Neumayer Station reached -2.3 degrees Celsius, marking the highest temperature recorded there in July since observations began in 1982 and occurring in the midst of the polar night, the peak of winter in Antarctica, as explained by Martin Radenz. This unusual warmth led to the formation of a clear ice layer about 2 millimeters thick over the previous day’s snow. “What occurs regularly in Central Europe during winter is rare in Antarctica during its dark polar night, where temperatures at Neumayer Station III typically drop below -30 degrees Celsius in July. Our observations over ice shelves are unprecedented,” stressed Radenz.
It didn’t take long for the value of remote sensing measurements to be acknowledged by the Alfred Wegener Institute (AWI), which operates the Neumayer station. The launch of OCEANET-Atmosphere marked the start of long-term profile measurements in this Antarctic region. Starting in early 2024, AWI will enhance its permanent observation capabilities with lidar and radar, ensuring continuity of the unique OCEANET data set. Dr. Holger Schmithüsen from AWI remarked, “The long-term climatological data concerning aerosols and cloud parameters at Neumayer Station will now extend into the vertical dimension.”
The results from this study have been summarized in the BAMS journal, showcasing the potential of the one-year dataset to illuminate the still poorly understood characteristics of clouds and aerosols over Antarctica. “However, the BAMS article merely offers an introductory look at some of the significant findings from the measurements. More detailed statistics and studies of the processes will follow,” stated Radenz. In the coming months, the comprehensive data gathered from Antarctica will be further analyzed and compared with existing datasets from southern Chile, Cyprus, Germany, and the Arctic. Researchers aim to uncover new insights regarding the differences between clouds in the far south versus those in the northern hemisphere. Many key climate research datasets are available for comparison. Since 2016, TROPOS has collaborated with the University of Leipzig to study clouds in the Arctic as part of the DFG Transregio “Arctic Amplification” (AC3-TR). Furthermore, increasing interest in southern hemisphere processes has emerged in recent years; for instance, Leipzig cloud researchers participated in the international Antarctic circumnavigation ACE in 2016/17 and extensive measurements were undertaken in southern Chile from 2018 to 2021. Two major measurement campaigns in and around New Zealand are being organized for 2025 and 2026: goSouth at the southern tip of the South Island and HALO-South with the German research aircraft HALO, alongside an expedition around New Zealand with the research vessel Sonne, will mark the next phase of experiments led by TROPOS. “TROPOS aims to provide crucial new insights for enhancing our understanding of aerosol-cloud-climate interactions in the pristine maritime southern hemisphere,” concluded Prof. Andreas Macke.
