Icy lakes, rugged rocks, vast steppes and harsh weather – Tierra del Fuego is known for its breathtaking nature. However, it was not the latter that attracted scientists to the southernmost tip of America, but the previously hardly-explored atmosphere of the southern hemisphere. The researchers collected data at altitudes of up to 90 kilometres to optimise models and better understand climate change.
months is how long the measurement campaign in South America takes.
scientists and technicians are in the field.
million euros is the budget of the campaign.
The Tierra del Fuego archipelago is the wind-blown southernmost tip of Argentina and Chile, about 1,000 kilometres from Antarctica. In September and November 2019, several atmospheric researchers and engineers moved their laboratories to this inhospitable area – or, to be more precise, into a draughty aircraft hangar in the city of Rio Grande on the main island of Tierra del Fuego and on board the research aircraft HALO. The aircraft was stationed there for the “SouthTRAC” measurement campaign and equipped with a globally unparalleled instrumentation.
The goal of the campaign: to obtain new data on the composition and exchange of atmospheric layers in the southern hemisphere. “Above all, we need reliable data on the composition and transport of trace gases, particularly at altitudes where the troposphere and stratosphere meet – that is, at about 8 to 15 kilometres. This region is crucial for also understanding climate change in the southern hemisphere and improving existing climate models,” explains Dr. Peter Preusse, physicist at the Jülich Institute of Energy and Climate Research (IEK-7). The researchers also want to close some of the gaps that still exist, for example with regard to air pollutants, ozone depletion and gravity waves.
Meticulously planned over two years, the campaign ran like clockwork on site. Surprising weather phenomena did not change this, nor did computer and car breakdowns, which were mastered professionally and sometimes unconventionally. Read more on the following two pages.
The SouthTRAC measurement campaign flights were coordinated by Jülich experts together with colleagues from the German Aerospace Center (DLR), the Karlsruhe Institute of Technology (KIT) and the universities of Mainz and Frankfurt. Other partners were the University of Wuppertal and Heidelberg University. A total of 13 instruments were accommodated on board the HALO research aircraft, including three precision instruments that are unique worldwide and were developed and built with Jülich participation: the GLORIA infrared spectrometer for measuring temperature, trace substances and aerosols; the FISH hygrometer for determining air humidity; and AMICA for measuring other trace gases.
During the polar night, the atmosphere above the poles cools down considerably. As a result, the polar vortex is formed, with winds of over 100 m/s at its edge. Gravity waves originate north of it over the Andes and south over the Antarctic Peninsula and then spread out into the polar vortex. To explore this, the research aircraft HALO flew into the polar vortex. By combining the GLORIA and ALIMA measuring instruments, the spread of the waves from the troposphere to the mesosphere could be tracked. A second goal was to study exchange processes between the troposphere and stratosphere. These can be quantified on the basis of concentrations of typical trace gases such as water vapour, carbon monoxide, CFCs and ozone.
They show up as billows and stripes in clouds: gravity waves – atmospheric disturbances that influence winds, temperatures and the chemical composition of the earth’s middle and upper atmosphere. These air oscillations occur, for example, when strong winds hit high mountains, such as the Andes or the mountain ranges of the Antarctic Peninsula. The waves are powerful: for example, they can weaken the polar vortex over the Antarctic. At an altitude of up to 80 kilometres, the vortex races at over 200 kilometres per hour and influences the climate all over the world. If it is disturbed or collapses prematurely – as was the case in the winter of 2019 – then, among other effects, the ozone depletion in the stratosphere is lower and the ozone hole is therefore much smaller than in normal weather conditions.
The researchers characterise the three-dimensional expansion and the structures of such gravity waves with the aid of the GLORIA spectrometer and the novel ALIMA laser, which radiates spectacularly from the roof of HALO up to a height of 90 kilometres. The campaign also focused on so-called planetary waves with wavelengths spanning half the earth. The data are also expected to clarify the extent to which these waves contribute to the exchange of air between the troposphere and stratosphere. This is because the exchange of air changes the distribution of trace gases such as water vapour and ozone in the upper troposphere and lower stratosphere. This distribution in turn influences how heat is absorbed by the atmosphere and dissipated into space or reflected back to the ground. These processes are thus key elements in understanding climate change.
A dark lining stretches over the horizon. It bears witness to the devastating forest fires in South America and Australia. During the transfer flights of the research aircraft HALO between Germany and Argentina, the measuring instruments on board occasionally recorded “such high concentrations of air pollutants like carbon monoxide, for example, as the colleagues had never seen before in their entire careers,” reports Jülich expert Dr. Jörn Ungermann. Degradation products of the various air pollutants are very long-lasting and, over time, even penetrate the stratosphere. According to the researchers, the effects of the large-scale fires on the climate are not yet foreseeable.
Not everything always runs smoothly. Even before the campaign really gets underway, the sea container is stuck in port, packed with special equipment to every nook and cranny. 50 metres of Internet cable are missing. There is a thick fog on the day HALO arrives. A computer with the data of three irretrievable measuring days refuses to cooperate. There are additionally the small dramas like mud and extreme wind that ruin rental cars and bring hikers to their knees. Then, however, the customs authorities come to an understanding after all; a local electrical dealer solders the missing cables together; the fog lifts; and the data can later be salvaged at Jülich. A farmer drags the rental car out of the mire, and all researchers return unharmed from their hiking tours to find answers on how to meet global climate targets.
Texts: Brigitte Stahl-Busse
Photos: Forschungszentrum Jülich/Peter Preusse, Vera Bense (Uni Mainz), DLR CC-BY 3.0, Video: Forschungszentrum Jülich, Grafic:Seitenplan