image: TROPOS Lidar of the OCEANET container during the polar night at MOSAiC.
Credit: Ronny Engelmann, TROPOS
Leipzig/Köln/Bremen. The Collaborative Research Centre “Arctic Amplification: Climate Relevant Atmospheric and Surface Processes and Feedback Mechanism (AC)³” is to enter its third funding phase. This was announced today (24 November 2023) by the German Research Foundation (DFG). From January 2024, the research network, which also includes the Universities of Bremen and Cologne, the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and the Leibniz Institute for Tropospheric Research (TROPOS), will continue its ground-breaking work for another four years. The overall aim is to make fundamental and significant advances in our understanding of Arctic amplification and improve the reliability of models used to predict the dramatic warming of the Arctic.
“Over the past 25 years, we have observed a drastic increase in near-surface air temperatures in the Arctic, which is two to three times more pronounced than global warming,” says Professor Manfred Wendisch from Leipzig University, spokesperson for the Collaborative Research Centre. This phenomenon, which the interdisciplinary network has been studying and trying to understand for eight years using various scientific methods, is known as Arctic amplification. Professor Susanne Crewell, deputy spokesperson from the University of Cologne, explains: “In recent years, we have been able to quantify seasonal differences and better understand the interaction of various feedback mechanisms that are thought to be the cause of Arctic amplification.” Dr Gunnar Spreen, deputy spokesperson from the University of Bremen, adds: “This is connected to a dramatic decrease in sea ice. In summer, we only have about half of the ice that we had 40 to 50 years ago. The (AC)³ is investigating which interactions between the atmosphere and ocean play a role here.”
What the researchers have found out so far
The scientists have used existing and new data to identify short-term changes and indications in Arctic climate variables. “The Arctic atmosphere has become significantly wetter. Storm activity has also increased regionally,” summarises Manfred Wendisch. In addition, winter warming has intensified in the regions around Svalbard and the North Pole, which has led to a decrease in the thickness of sea ice in the Fram Strait and snow depth on the ice.
The research aircraft HALO and the polar aircraft Polar 5 and 6 in conjunction with the icebreaker Polarstern have been used on expeditions to the Arctic. The latter were part of the MOSAiC expedition led by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). The Collaborative Research Centre (AC)³ was the main German university contribution to MOSAiC.
Future priorities and projects
The Collaborative Research Centre / Transregio 172 “Arctic Amplification (AC)³” will answer three central questions in its third phase:
• What are the main causes and to what extent do these contribute to Artic amplification?
• How do changes in the transport of air masses impact the weather and climate in the Arctic and mid-latitudes?
• What trends can be identified that are caused by Arctic amplification and how will they develop in a future, warmer climate?
To better link their results in the future, the researchers are developing cross-cutting themes to answer key questions in four key areas: the vertical temperature gradient, surface processes, Arctic mixed-phase clouds, and transport and transformation of air masses.
The main objective of the third phase of the Collaborative Research Centre (AC)³ is to bring together the numerous observational and modelling results from the previous phases in order to make fundamental and significant advances in our understanding of Arctic amplification. In the coming years, the interdisciplinary network’s research questions will continue to provide the basis for ground-breaking insights into arctic climate change. These will also contribute to addressing the challenges of climate change on a global scale.
The hygroscopicity of aerosol particles is an important factor in the effect of aerosol particles on the climate and thus also for forecasting changes to the climate using global climate models. "The capacity to hold water depends on the composition of aerosol particles, which can vary considerably in the atmosphere. However, in our study we were able to show that simplified assumptions can be made for the consideration of hygroscopicity in climate models," explains Mira Pöhlker. She is in charge of the "Atmospheric Microphysics" department at TROPOS and is a professor at the University of Leipzig. According to the aerosol and cloud researcher, this is the first study to use measurement results from across the world to show that a simple linear formula can be used without creating huge uncertainty in climate models.
TROPOS contribution to (AC)³
In the third phase, TROPOS will extend the coverage of Arctic cloud cover and its climate effects from the MOSAiC expedition to the entire Arctic and supplement detailed measurements of the Arctic boundary layer as a key climatic region. Aerosol climate models will be used to investigate the effects of anthropogenic and natural aerosols on the warming of the Arctic climate, with a particular focus on changing aerosol patterns and their significance for air mass transport and the energy balance. A further contribution will investigate the changes in Arctic cloud cover caused by cold air outbreaks using high-resolution aircraft observations and long-term satellite data. Overall, with its focus on aerosols, aerosol-cloud interactions and the radiation balance, TROPOS contributes to the understanding of changes in the Arctic and the connections with the global climate system.