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Mountain glaciers and polar ice – those parts of the Earth that are covered with ice and snow are relevant to our climate and to climate change on various levels. They cool the Earth by reflecting the sun’s radiation back into space. They also store water – water that flows into the oceans as temperatures increase and causes sea levels to rise.
Ice cores: an archive of the Earth’s climate
At the same time, the polar ice caps that have built up over millions of years serve as an archive of our planet’s climate. Ice cores which scientists from the Alfred Wegener Institute (AWI) in Bremerhaven extract from the ice sheets at depths of up to 3,000 metres provide information about the climate hundreds of thousands of years ago. In the same way that historians draw conclusions about the present and future from their studies of the past, the AWI researchers learn from the ice cores how the climate might change in the future.
Filling gaps in weather and climate models
It is not only the ice itself but also the atmospheric layers above it that are of great interest to climate researchers. Despite the huge volumes of global climate data, there are still gaps. For example, air movements in the atmosphere between the surface of the Earth and an altitude of roughly 500 to 2,000 metres are not sufficiently charted in the weather and climate models. And yet it is in this planetary boundary layer that much of the heat and water vapour exchange takes place.
The physicist Burkhard Wrenger has developed drones with a view to filling these gaps. A professor in the field of autonomous sensor systems at Ostwestfalen-Lippe University of Applied Sciences (OWL), Wenger flew his drones on the island of Hailuoto in northern Finland in February 2018. A popular seaside resort in the summer, the Baltic Sea churns up icebergs up to six metres high in the winter here. "Our goal was to obtain precise data that would allow us to better understand how ice influences climate", Wrenger explains.
Weather data from drones
Wrenger and his colleagues sent the autonomous quadcopter drones up to altitudes of 1,800 metres. The team was made up of computer scientists and environmental engineers from the OWL and the University of Tübingen plus colleagues from the University of Bergen in Norway and in the USA. The probes sent temperature, humidity, atmospheric pressure and wind readings back to the ground station. During their measurement flights, which last up to 30 minutes, the drones ascend at a speed of roughly one metre per second. This allows them to deliver a much fuller picture than weather balloons.
The measurements were conducted during the coldest hours of the day: from shortly before sunset in the late afternoon until the early morning. Turbulence in the lower atmospheric layers close to the ground is at its most dynamic during these transitional periods. "We had expected temperatures as low as 26 degrees below zero and high atmospheric humidity", says Wrenger. Nonetheless, they were surprised by the effects: their fingers began to freeze within half a minute without gloves. A layer of ice formed on the rotors in a matter of seconds.
Understanding what climate researchers need
Burkhard Wrenger has been developing drones for climate research for around ten years now. "We now understand pretty well what climate researchers need", remarks Wrenger. This is not only important for the measurement flights, as part of his team’s job is also to prepare the meteorological data. The measurements from the individual probes have to be compared, sorted and pre-processed so that users can see at a glance for example what time a drone flew at what altitude. The next steps – analysing the data scientifically and feeding it into climate models – are done by meteorologists from several European research groups, and by the researchers from Bergen who are coordinating the ISOBAR project.
Meanwhile, our specialist in autonomous flight systems and sensors wants to turn his attention to other things. "The biggest challenge is the flight time", explains Wrenger. The drones are more than a metre in size and weigh up to five kilograms, depending on the probes they are fitted with. Their batteries have enough power to keep them in the air for over an hour at temperatures of around 20 degrees. They run out of charge after just 30 minutes at the Artic temperatures in northern Finland, however – and can only fly that long because the scientists pre-warm the batteries in their anorak pockets.
German Climate Computing Center (DKRZ)
The measurements carried out by climate researchers around the world produce huge quantities of data. In their turn, the climate models into which they are fed require gigantic computing capacities. Scientists can access such high-performance computers and data storage facilities at the German Climate Computing Center (DKRZ) in Hamburg, where they can simulate climate-relevant processes in the atmosphere, on land and in the ocean and can calculate future scenarios. The DKRZ supports them with optimising models and analysing, visualising and archiving climate data.www.dkrz.de