Dramatic warming in the Arctic - HALO-(AC)3 field campaign investigates an alarming phenomenon

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.

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 using local, ground-based instruments, as there are only a limited number of meteorological measurement stations in the central Arctic region. Therefore, three measurement aircraft will be deployed 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 summarizes 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.’

Coordinated measuring flights with three research aircraft Three German research aircraft will be used to perform measurements for HALO-(AC)3. The aircraft are equipped with instrumentation that can survey the entire atmosphere from the ground up to an altitude of 10 kilometres. The most important measurement parameters include cloud properties, temperature, and humidity profiles, energy fluxes and the properties of aerosol particles and trace gases. Susanne Crewell, an atmospheric researcher at the University of Cologne, explains: ’By coordinating the flight patterns of the three aircraft, we can track the air masses as they evolve in space and time. These measurements make it possible to take a closer look at the smallest cloud structures, all the way down to individual cloud particles, and to investigate the effect of Arctic sea ice on cloud properties. By combining various measurements, we will be able to obtain an almost complete picture of the air masses under investigation.’ Important tools for this are what are referred to as ’dropsondes’, which are released from the aircraft and descend to the ground on small parachutes. As they descend through the atmosphere, they acquire measurements of temperature, air pressure and humidity.

The focus of the scientists from the University of Cologne is on new observation techniques and modelling to better understand and predict the role of clouds and precipitation in the Arctic climate system. ’We will carry out special simulations with weather models whose resolution is fine enough to at least partially resolve clouds’, said Vera Schemann from Crewell’s team. On the one hand, they will help the scientists by providing additional information for flight planning, and on the other hand they can be used to investigate how well the mdoels take into account the changes in the air masses. Combining the new observations and special simulations will allow them to analyse which processes in the air masses decisively shape the clouds and how the air transports influence the Arctic.

Who are the partners involved?

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, Ludwig-Maximilians-Universität 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. HALO-(AC)3 combines the research on ’Arctic Amplification’ within the infrastructure priority program on the scientific use of HALO and the Transregional Collaborative Research Centre (AC)3 (ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes and Feedback Mechanisms). Both of these major projects are funded by the German Research Foundation (Deutsche Forschungsgemeinschaft; DFG).

High resolution photos for media use free of charge if sources are acknowledged: https://speicherwolke.uni-leipzig.de/index.php/s/87LAGYMKNznNjzB

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