A whale on Arctic expedition


The regular tethered balloon measurements conducted during the international MOSAiC expedition, are now being enhanced by a larger balloon. It can be used to measure clouds and atmospheric radiation up to 1,5 km above the ice.

07/10/2020 · Umweltwissenschaften · Leibniz-Institut für Troposphärenforschung · News · Forschungsergebnis

After a preparatory period of about three years, observations that play an important role in studying the atmosphere in the Arctic will start at the end of June:

For the first time the regular tethered balloon measurements conducted during the international MOSAiC expedition, are now being enhanced by a balloon that is considerably larger. With a capacity of 90 cubic metres it can be used to measure clouds and atmospheric radiation up to one and a half kilometres above the ice. The system was prepared by the Leibniz Institute for Tropospheric Research (TROPOS) and the University of Leipzig, already used and successfully tested on a Polarstern expedition in the Arctic in 2017. The tethered balloon will be an important platform for atmospheric measurements at MOSAiC above the ice floe during the melting phase in the Arctic early summer, also because the originally planned measurements with aircraft from Svalbard had to be suspended due to the corona pandemic.

With these measurements, researchers from Saxony contribute to the understanding why the atmosphere in the Arctic is warming much more than in other regions of the world and how quickly climate change takes place around the North Pole. "The data collected with the measurements by TROPOS and the University of Leipzig in the Arctic during the MOSAiC expedition are an important component in international climate research," says Saxony's Minister of Science Sebastian Gemkow. "Clouds are the biggest factor of uncertainty in climate scenarios for the future and Leipzig has developed into an important player in cloud research in past years due to its great local expertise".

For example, the German contribution to the European research infrastructure for aerosol, clouds and trace gases (ACTRIS) is coordinated by TROPOS. The Collaborative Research Centre "Arctic Climate Change (AC)³" of the German Research Foundation (DFG) under the leadership of the University of Leipzig is an essential part of the current Arctic expedition.  Since 2016, scientists have been investigating which influence clouds and the associated processes in the atmosphere have on the fact that the Arctic is warming more than any other region on earth and has become a 'hot spot' of climate change. "The MOSAiC expedition is also a unique opportunity for us to better understand the complex feedback mechanisms between ocean, sea ice and atmosphere, because many disciplines closely work together during the expedition. 18 out of 20 scientific projects of the Collaborative Research Centre therefore participate in the data collection and evaluation of MOSAiC. The DFG is supporting the expedition with considerable financial resources," emphasises Prof. Manfred Wendisch, Director of the Institute of Meteorology at the University of Leipzig, who is the spokesperson for the German Research Foundation's Collaborative Research Centre.

The „floating white whale “

For the staff change, the research vessel Polarstern temporarily left its ice floe, which has been used since October 2019, in mid-May, heading for Spitsbergen. As soon as the new team of leg 4 has taken over and 14 tons of food are stored on board, they will return to the ice from Spitsbergen. Depending on the state of the ice floe, observations will then continue on the old floe or Polarstern will search a new, more solid floe for the coming months.

Again, the floe will then be equipped with various instruments. Since the beginning of the expedition, measurements with a smaller tethered balloon of the Alfred Wegener Institute have also been carried out. For the first time, this is now supplemented by a 14-metre-long tethered balloon, which is tied to the ground (" tethered") by an extendable and retractable rope and can ascend to 1500 m altitude. The balloon, including the measuring instruments attached to it, was named BELUGA because the tethered balloon reminds of a white whale. BELUGA stands for "Balloon-bornE moduLar Utility for profilinG the lower Atmosphere" - a carrier platform with which devices are transported from the ground into the lower atmosphere. Its volume of 90 cubic meters allows equipment loads of up to 20 kilograms, which are secured by an additional 3 kilometers long and 4 millimeters thin special rope.  Various especially designed probes and collectors are planned as workloads for the measurement of turbulence (TROPOS), atmospheric radiation (University of Leipzig), cloud microphysics (University of Leipzig & TROPOS), aerosol (TROPOS), cloud water (University of Stockholm in cooperation with TROPOS), particle filter (TROPOS) and other probes from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and the British Antarctic Survey (BAS). A cuboid aerosol box ("CAMP - Cubic Aerosol Measurement Platform") will measure the soot content in the Arctic atmosphere. TROPOS and the University of Leipzig closely cooperate  with the Technical University of Braunschweig, which has installed similar measuring instruments on its helicopter towed probe “Helipod”. This makes the tethered balloon an important measuring platform for investigating the lower layer of the atmosphere with its deep clouds, which is so important for warming the Arctic. The tethered balloon was constructed by a specialized company in Augsburg. Thanks to new materials, a revised version is now able to transport twice the weight of the 2017 version. The previously used balloon was extensively tested in winter 2018/19 and the new one in summer 2019 in Melpitz near Leipzig. Both have been on board since the launch of Polarstern in September 2019 and are waiting for their mission.   

For MOSAiC, a smaller tethered balloon of the AWI has been used so far. "Miss Piggy" can carry payloads of up to 4 kilograms - including a turbulence sensor from TROPOS: "Initial data was already transmitted to us by AWI in February. The system coped well with the cold and harsh conditions of the polar night and delivered valuable high-resolution data. Extremely low-turbulence altitude regions alternate with well-mixed layers, resulting in very complex layering of the lower 100 metres of the atmospheric boundary layer during the polar night," says Dr. Holger Siebert of TROPOS.

Arctic test three years ago

The large balloon from TROPOS, previous to BELUGA’s predecessor model, experienced its premiere in 2017: Under the leadership of Prof. Andreas Macke, Director of TROPOS, the Polarstern expedition PS106.1 took place I this year. During this expedition, the German research icebreaker had already been drifting for three weeks on an ice floe through the Arctic near Spitsbergen. In the project PASCAL (Physical feedbacks of Arctic PBL, Seaice, Cloud And Aerosol), within the framework of the Collaborative Research Centre "Arctic Climate Change (AC)³" of the German Research Foundation (DFG), interactions between sea ice, clouds and aerosol in the transition zone between open ocean and sea ice were investigated to learn more about the decrease of Arctic sea ice in summer. In this process, components for the current MOSAiC expedition were also tested - including the balloon. "Since then we have optimized many small details in order to measure the air layers near the ground as exactly as possible. But the principle has proved successful and makes us optimistic that we can make an important contribution to a better understanding of what and how clouds form in the Arctic. And this will help us later to know more about the role of clouds in the dramatic melting of the Arctic," explains Andreas Macke.

From bottom to top and back again

The large balloon is an important component in a long sequence of very complex measurements to investigate the formation of clouds. With the break-up of the ice in spring, the dynamics in the Arctic atmosphere are clearly gaining strength. The water of the ocean emits particles and gases, from which droplets and finally clouds are formed, which then influence atmospheric radiation and temperature. Depending on altitude and composition, these clouds can cool or accelerate climate change. "Therefore it is important that we study the whole spectrum from seawater to clouds. To this end, samples will be taken from the water, surface film and air to find out which organic components from the ocean influence the atmosphere. Together with the University of Stockholm, we want to 'capture' the cloud water with a small balloon collector. The aim is to measure marine sugars from the ocean and ice germs in cloud water," explains Dr. Manuela van Pinxteren from TROPOS, who is investigating the surface layer and is looking forward to analysing the samples in the laboratory in Leipzig from autumn onwards. Then a comparison between the tropical and arctic Atlantic will also be necessary, because in 2017 similar measurements already existed on the Cape Verde Islands. The interdisciplinary MOSAiC expedition offers the great opportunity to better understand the very complex interactions between the biology in the ocean, the melting of sea ice and the warming of the atmosphere due to many participating disciplines.

Unique long-term observation of the atmosphere by laser

While the experiments on the ice floe heavily depend on the weather and the melting of the ice, the measurements on board Polarstern are, so to speak, the solid rock in troubled waters. Since the beginning of the expedition, the atmosphere has been studied from the foredeck of the icebreaker: Researchers from the Cooperative Institute for Research in Environmental Sciences (CIRES) in the USA and TROPOS are exploring the atmosphere from the ground using remote sensing methods such as radar and lidar. TROPOS operates such a lidar - a light radar that can use laser pulses to measure dust particles from the ground far up into the polar stratosphere (15-17 km altitude). MOSAiC here offered a novelty: For the first time, a multi-wavelength lidar was used during the polar night in the central Arctic and showed several layers of smoke. The smoke is apparently coming from human sources and mainly from forest fires in the boreal forests around the Arctic. Especially in Siberia, the last winter was exceptionally warm and the spring very dry. According to media reports, the extent of the fires there has reached record levels in 2019/20 and increased ten times compared to last spring. The consequences can be felt for a long time in the atmosphere at the North Pole - until the polar winter. "Evaluation is still ongoing. We were surprised at how stable these layers hover above the North Pole for more than six months. Nobody before us has been able to see it like this because nobody has ever measured with such instruments in the heart of the Arctic under these extreme conditions of the polar night," emphasizes Dr. Albert Ansmann, who leads the lidar group at TROPOS and conducts measurements worldwide.  And Dr. Matthew Shupe (CIRES, University of Colorado and NOAA-ESRL), who is co-leader of the upcoming expedition leg and also co-leader of the atmosphere team of MOSAiC, joins: „We are proud to bring together leading research groups worldwide as we continue with MOSAiC. During the seasonal transition into summer we will have exciting new opportunities to measure the vertical atmospheric structure, aerosol profiles, cloud radiative effects and much more from a large tethered balloon. Collectively these measurements will offer important new insights into the changing Arctic.“

An expedition of superlatives

In order to be able to study all research topics for one year, an enormous logistical effort is required: The MOSAiC expedition led by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) is associated with unprecedented challenges. An international fleet of 4 icebreakers supplies the team on this extreme route. A total of 600 international participants, half of them scientists, will accompany the mission. The budget of the expedition is around 140 million euros. In the course of the year, about 300 scientists from institutions in 29 countries will be on board. The questions that the researchers intend to investigate during the expedition are closely linked. Together they want to explore the entire climate system in the Central Arctic for the first time. They collect data in the five sub-sectors atmosphere, sea ice, ocean, ecosystem and biogeochemistry to understand the interactions that shape the Arctic climate and life in the Arctic Ocean. "This expedition is ground-breaking. Never before has there been such a complex Arctic expedition. For the first time, we measured the climate processes of the Central Arctic in winter. The Arctic is the "weather kitchen" for our weather in Europe. Extreme weather conditions such as winter outbreaks of Arctic cold air reaching us or extremely hot phases in summer are also related to changes in the Arctic", explains expedition and project leader Prof. Markus Rex from the Alfred Wegener Institute (AWI).

The expedition to join for all

News directly from the Arctic is given via the MOSAiC channels on Twitter (@MOSAiCArctic) and Instagram (@mosaic_expedition), hashtags #MOSAiCexpedition, #Arctic und #icedrift. Further information about the expedition on: www.mosaic-expedition.org. In the MOSAiC web app, the drift route of Polarstern can also be followed live: follow.mosaic-expedition.org

Current information on the participation of Leipzig researchers in MOSAiC on: https://www.tropos.de/mosaic/

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