MOSAiC On Air – This Year’s First Airborne Campaigns Over the Central Arctic

by Daniel Butkaitis and Kirstin Werner, Alfred Wegener Institute

After five months of compulsory break due to the COVID-19 pandemic, the polar research aircraft Polar 5 and Polar 6 were finally able to launch their airborne campaigns from Svalbard on August 30. These were the first survey flights the aircraft maintained by the German Alfred Wegener Institute could carry out over the Arctic since Svalbard had been closed in spring. The three-week campaign, which was part of the MOSAiC expedition, aimed at collecting data on sea-ice thickness and from the atmosphere to improve our understanding of essential atmospheric processes that lead to cloud formation over the Arctic.

In total, four survey flight campaigns had been planned for this year to support the MOSAiC one-year ice drift through the central Arctic. Two of the campaigns were supposed to be launched during spring, when the Arctic sea ice would have reached its maximum extent.  However, the spring campaign had to be cancelled due to the Coronavirus pandemic. Another two flight campaigns were planned for summer when the Arctic sea-ice extent will have reached its minimum. Thanks to the support by the Norwegian government and the Governor of Svalbard the summer campaign flights were finally able to set off on August 30 from Longyearbyen airport, Svalbard.

During their three-week campaign, both research aircraft performed a total of 17 flights over the Arctic Ocean north and west of Svalbard, with each flight lasting between three and seven hours. Initially, it was planned to follow the trajectory of the MOSAiC floe and the air-mass trajectories passing RV Polarstern. Although RV Polarstern eventually changed her route and moved outside the possible flight range of the aircraft, the collected atmospheric data will well supplement the MOSAiC mission.

Clouds Over the Arctic
The ACA campaign (ACA stands for Airborne observation over the Central Arctic) on board Polar 5 addressed the following key questions: How do clouds form over the Arctic, and which components, especially aerosol particles and turbulent eddies, play a significant role in the process? Recent studies have shown that clouds play an important role in the warming of the Arctic atmosphere. In the mid-latitudes, deep clouds have mainly a cooling effect. Different in the Arctic, the clouds heat the air above the sea ice. However, current atmospheric models are most likely to underestimate the clouds’ influence on rising air temperatures in the Arctic. The measurements will be used to investigate if clouds above sea ice warm the environment more than models predict. ACA is part of the YOPP-endorsed (AC)3 project (or: ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms) which is a joint collaboration between various German research institutes and universities led by the University of Leipzig.

Manfred Wendisch who jointly with Andreas Herber from AWI leads the ACA mission describes its challenges as follows: “The local weather was determined by frequent low-pressure systems circling the island of Spitsbergen. That caused low cloud base levels and low visibility at the airport which partly prevented us from flying.” The changing route of RV Polarstern had also been an issue. “One of the objectives of our campaign – the link of local Polarstern measurements with air mass evolution to and from Polarstern – could therefore only partly be achieved.

Satisfied with Mother Nature
Despite the difficulties, the research aircraft succeeded in collecting valuable dropsonde data and perform numerous cloud measurements. “They will be important to quantify the cloud prediction skills of the NWP models“, says Manfred Wendisch who is professor for meteorology at the University of Leipzig, Germany, overall being happy with the outcome of the flights “We obtained a nice data set to look at the influence of sea ice versus open ocean conditions on cloud evolution and on the effects of the radiative budget during late summer. We were quite satisfied with the cases mother nature presented us for our measurements.”

Summer Sea-Ice Export Through Fram Strait
Focus of the Polar 6 campaign was to analyse thickness and surface characteristics of the sea ice in the central Arctic as well as in the Fram Strait, a narrow passage connecting the North Atlantic with the Arctic Ocean. The information collected during flights will be used to examine the link between thickness variability, sea ice age, and the source area of sea ice. Together with satellite-based sea-ice information, results will be used to quantify the summer sea-ice export through Fram Strait. For the measurements, researchers mainly relied on the so-called EM-Bird instrument. EM-Bird is an electromagnetic measuring device, with the shape of a torpedo, which is attached beneath or behind the plane at a height of about 15 metres during the flight. Polar 6 was also equipped with the MACS/DLR camera developed by the University of Münster. Germany. The aerial shots will be used to construct high resolution Digital Elevation Models (DEMs) of the Arctic area.

The German Alfred Wegener Institute (AWI) has carried out sea-ice thickness measurements since almost two decades as part of their long-term data program called IceBird. AWI physicists are regularly surveying the Arctic sea-ice twice a year – at the end of the winter, when the sea ice is reaching its maximum extent, as well as in the summer when the sea-ice extent shrinks to its annual minimum.

AWI sea-ice scientist and leader of the IceBird campaign (see below) Thomas Krumpen, was excited about the upcoming results from this year’s airborne observations. “This summer, there’s also the exciting question of whether the conditions of the ice floes that were investigated during the MOSAiC expedition stand out in comparison to our long-term data. In other words: whether the ice was generally thinner or thicker than in the past; whether the high summer temperatures had any major effects on it; and whether the rapid drift led to an unusually high number of pressure ridges” (quoted from Meteorological Technology International).