LMU: Climate researchers survey dramatic warming in the Arctic

In mid-March 2022, the large-scale international HALO-(AC)3 research campaign will begin investigating transformations of air masses in the Arctic. Three German aircraft will be deployed, scientists from the UK and France will also be involved during joint flights with two further aircraft. The team of researchers will be focusing particularly on northwards-flowing warm air reaching into the central Arctic, which are often called warm air intrusions. The counterpart, cold air outbreaks with southwards-moving cold air from the Arctic, will also be investigated. The goal is to investigate the processes causing the above-average increase in temperatures in the Arctic during the last decades. At two to three degrees Celsius over the last 50 years, this increase is much larger than the warming that has taken place in other regions on Earth. This phenomenon is referred to as Arctic amplification. The effects of this increase in temperature are not limited to the climate system in the Arctic, but are suspected to modify the regional weather in the mid-latitudes, as well. Thus, the HALO-(AC)3 campaign aims to contribute to a better understanding of the processes behind the dramatic climate changes that are currently taking place in the Arctic. During the first measuring flights since 12 March 2022 a massive warm air intrusion into the Arctic has been observed. At this event, several unusual phenomena have been detected, such as heavy rain over sea ice and massive clouds, reaching almost as high as in the tropics. With the arrival today of further research aircraft, planned coordinated measurement flights will begin on 19 March 2022, to better understand the complexity of these events.

Innovative observation methods
Manfred Wendisch from the Institute for Meteorology at Leipzig University is the scientific coordinator of the five-week HALO-(AC)3 measuring campaign, which will study changes in air masses on their way into and out of the Arctic. What exactly happens to these air masses, particularly with regard to cloud formation, will be observed in detail using state-of-the art instruments. These changes to air masses cannot be characterized by local, ground-based instruments, as there are only a limited number of meteorological measurement stations in the central Arctic region. For this reason, three measurement aircraft will be applied as part of HALO-(AC)3 to observe the changes of the air masses on their way into and out of the Arctic. The researchers aim to determine changes to the air masses using a quasi-Lagrangian observation method. In this technique, each flight pattern is adapted to the direction of movement of the relevant air mass, allowing changes to clouds, humidity, temperature and many other parameters to be measured directly. The data obtained in this way will be used to assess the accuracy of numerical weather forecasting models, which are necessary for predicting the future changes of the Arctic climate. Thus, the campaign will help to close an important gap in climate research knowledge, which was identified by the Intergovernmental Panel on Climate Change (IPCC) in the second part of its latest assessment report.

Manfred Wendisch summarises the goal of HALO-(AC)3 as follows: “Predicting the future of the Arctic climate remains a challenge. We want to carry out an extensive flight campaign – HALO-(AC)3 – that uses innovative observation methods to help reduce major uncertainties in the projection of future climate development in the Arctic.”

“Clouds play a very important role in the Arctic climate,” says Prof. Bernhard Mayer, atmospheric scientist in the Faculty of Physics at LMU. “The exact composition of the cloud, the relative proportions of liquid droplets and frozen ice particles, decisively determine the reflection of sunlight and the lifetime of the cloud — processes that must be understood to be able to predict Arctic climate with precision. Our team is on board the HALO research aircraft with a new measuring technique for quantifying precisely this distribution of liquid water and ice.”

Alarming observations from current HALO flights
Since 12 March 2022, HALO already performed a series of very successful research flights from Kiruna over the Norwegian and the Greenland Sea as well as the Fram Strait to the North Pole. A massive warm air intrusion into the Arctic has been investigated and so far, several unusual phenomena have been observed during these flights, for example, heavy rain over sea ice. This might have serious implications on a possible early melting of the sea ice, and this in the mid of March. Furthermore, massive clouds have been observed, reaching almost as high as in the tropics. Surface temperatures in the Fram Strait have been more than 20 degrees Celsius higher during the current flights than expected from the long-term records. It is not just the intensity of the currently observed warm air intrusion, but also the duration, which seems unusual. During Tuesday and Wednesday of this week further moisture transport into the Arctic has been observed, which is called “Atmospheric River”, likely causing record precipitation and even more warming of the entire Arctic. There are indications from forecast products that the sea ice will be seriously disturbed by this massive warming event. The scientists on site are truly excited to witness further major events and hope to be able to follow them further on in the days to come. As the polar aircraft will arrive at Svalbard on 18 March 2022 coordinated measurement flights could then be all the more valuable to better understand the complexities of these events.

HALO-(AC)3 is a joint research campaign by Leipzig University, the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, the Leibniz Institute for Tropospheric Research, the Max Planck Institute for Meteorology and Chemistry, LMU Munich and the universities of Bremen, Hamburg, Cologne and Mainz, together with international partners. More than 100 scientists from 12 countries will take part in this research project.