The main question the ASCCI (Arctic Springtime Chemistry-Climate Investigations) measurement campaign seeks to answer is how ozone and water vapor in the upper troposphere and lower stratosphere - i.e. at altitudes between around five and 15 kilometers - themselves influence and are in turn influenced by Arctic climate change. To this end, the campaign specifically investigates the processes taking place in spring, including the depletion of stratospheric ozone. The density of the ozone layer above the Arctic fluctuates over the course of the year and can thin out in spring when chemical and meteorological conditions coincide.
"There are warmer and colder winters in the stratosphere; the variability from one year to another is quite normal. What we are also witnessing is that the stratosphere is getting increasingly colder due to the rise in greenhouse gases, while temperatures on the ground and in the troposphere continue to increase," says Professor Björn-Martin Sinnhuber from KIT's Institute of Meteorology and Climate Research, who is coordinating the campaign together with Goethe University Frankfurt's Professor Andreas Engel. In years with a cold stratosphere especially, processes occur that resemble those of the Antarctic ozone hole, and a significant part of the Arctic ozone layer can be destroyed.
"This winter has so far been characterized by unusually cold conditions in the Arctic stratosphere, i.e. the layer of air above about 10 kilometers. Although the concentrations of many chlorofluorocarbons and other ozone-depleting substances in the atmosphere are declining as a result of international regulations, since these gases are very long-lived in the atmosphere, this process takes a very long time," says Engel. "The measurements we conduct at Goethe University quantify how much ozone-depleting chlorine and bromine is present in the stratosphere - and the data show that this amount suffices to trigger chemical processes in these cold conditions, which in turn can lead to ozone depletion." At the same time, following the eruption of the Hunga-Tonga underwater volcano three years ago, there is still significantly more water in the stratosphere than normal, says Engel. As part of the ASCCI measurement campaign, the researchers also want to investigate how this affects the ozone layer.
In spring, air pollutants in particular are transported into the Arctic, where they can act as short-lived greenhouse gases. The campaign seeks to better understand these processes using targeted measurements. The measurement flights will be carried out with the HALO research aircraft, which is stationed in Kiruna in northern Sweden until April.
Better understanding ozone depletion in the Arctic and its influence on the mid-latitudes
On board HALO, Goethe University operates a proprietary device that measures a variety of halogenated gases, which in turn are the source of the ozone-depleting chlorine and bromine in the stratosphere. "We want to understand how the chlorine and bromine released from the halogenated gases affect the ozone in the Arctic stratosphere, and whether this also has an impact on the mid-latitudes in which we live," Engel explains. "If air from the Arctic with a low ozone content is mixed with that prevailing in our mid-latitudes, this can also impact the ozone shield above us, which protects us from the sun's dangerous UV radiation."
In addition to Goethe University Frankfurt and KIT, Forschungszentrum Jülich, German Aerospace Center (DLR) and the universities of Heidelberg, Mainz and Wuppertal are also part of the ASCCI campaign.
About HALO
The research aircraft HALO (High Altitude and Long Range Research Aircraft) is a joint initiative of German environmental and climate research institutions. HALO is funded by grants from the Federal Ministry of Education and Research, the German Research Foundation (DFG), Helmholtz Association, Max Planck Society, Leibniz Association, the free state of Bavaria, KIT, Forschungszentrum Jülich and German Aerospace Center (DLR), which acts as both the aircraft's owner and operator.
Background information
ASCCI measuring campaign: https://halo-research.de/sience/halo-missions/current-missions/ascci/
HALO research aircraft: https://www.dlr.de/en/research-and-transfer/projects-and-missions/halo-high-altitude-and-long-range-research-aircraft
Picture download:
http://www.uni-frankfurt.de/168920497
Caption: The HALO research aircraft lands in Kiruna, Sweden. The research flights over the Arctic take off from there. The photo is from an earlier mission. Photo: DLR (CC BY-ND 3.0)
