The German research aircraft HALO, a pinnacle of atmospheric science and airborne measurement technology, is poised for a groundbreaking mission in the pristine skies of the Southern Hemisphere. Currently stationed at its home base at the German Aerospace Center (DLR) in Oberpfaffenhofen, HALO is being meticulously prepared for deployment to New Zealand, where it will embark on the ambitious “HALO-South” scientific campaign. This mission, commencing in September, represents a critical advancement in the study of atmospheric dynamics, focusing specifically on the intricate interactions between clouds, aerosols, and radiation above the Southern Ocean — a region pivotal to Earth’s climate system yet poorly understood due to sparse observational data.
HALO-South is unprecedented in scope for a German research aircraft, marking the first time that such a sophisticated airborne platform has investigated the atmospheric compositions and processes over the South Pacific and the adjacent Southern Ocean at such southern latitudes. For five continuous weeks, HALO will conduct intensive measurement flights originating from Christchurch, New Zealand, targeting one of the most remote and climatically significant oceanic regions on the planet. This mission promises to fill critical gaps in the global climate knowledge base, with funding principally provided by the German Research Foundation (DFG) and supported by contributions from leading scientific institutions including the Max Planck Institute for Chemistry (MPIC) and the German Aerospace Centre (DLR).
One of the principal scientific motivations behind HALO-South lies in the unique atmospheric conditions prevailing in the Southern Hemisphere. The Southern Ocean surrounds Antarctica and is recognized as one of the cloudiest regions on Earth. Unlike the Northern Hemisphere, which is heavily influenced by industrial and urban emissions, the Southern Hemisphere is comparatively free from anthropogenic pollution. This cleaner atmosphere presents an exceptional natural laboratory to directly observe aerosol-cloud interactions uninfluenced by the complexity of human-sourced aerosols. Since cloud microphysics and their interactions with aerosols critically influence Earth’s radiation budget and climate feedback processes, understanding these relationships in a cleaner environment can inform and refine global climate models, which have largely been developed based on Northern Hemisphere data.
Current climate models and atmospheric simulations exhibit significant uncertainties when representing clouds in the Southern Hemisphere, largely due to a lack of direct measurements. Clouds over the Southern Ocean tend to contain more liquid water and less ice compared to their Northern Hemisphere counterparts, a discrepancy arising from the limited availability of cloud condensation nuclei particles in the cleaner southern atmosphere. This lack of data has perpetuated a longstanding gap in climate science, impeding accurate forecasts about how clouds influence radiation and precipitation patterns in these regions. HALO-South aims to close this gap by deploying a robust suite of twenty-two specialized scientific instruments aboard the aircraft to capture comprehensive data on aerosol properties, cloud microphysics, and radiation interactions.
Led by Professor Mira Pöhlker of the Leibniz Institute for Tropospheric Research (TROPOS) and the University of Leipzig, the mission integrates expertise from eight prestigious research institutions across Germany, encompassing atmospheric physics, chemistry, and meteorology. The nine participating entities include TROPOS, the Leipzig Institute for Meteorology, Johannes Gutenberg University Mainz, Goethe University Frankfurt, Max Planck Institute for Chemistry, Karlsruhe Institute of Technology, the German Aerospace Center, and Forschungszentrum Jülich. Operating with 176 planned flight hours, the campaign will collect unprecedented in situ observations from high altitudes, capturing atmospheric conditions that are otherwise inaccessible through ground stations or satellite remote sensing alone.
The HALO aircraft, operated by the DLR’s Flight Experiments (FX) unit, boasts state-of-the-art technology expressly designed for atmospheric research. Since entering service in 2012, HALO has contributed to multiple high-impact campaigns focused on aerosol-cloud-radiation interactions, yet its prior ventures into southern latitudes have been limited. HALO-South represents not only a geographical expansion but also an intensification of measurement complexity, with the mission targeting the full life cycle of clouds—from nucleation processes initiated by aerosols to cloud growth and eventual dissipation, alongside detailed characterization of radiative effects caused by cloud dynamics.
A crucial synergy underpins the HALO-South efforts, with ground-based measurements conducted in New Zealand complementing airborne data. The University of Canterbury and MetService New Zealand are partnering closely to provide baseline observations through remote sensing infrastructure located in Invercargill, at the southern tip of New Zealand’s South Island. This integration is further expanded through active contributions from Leipzig and Canterbury universities at the Tāwhaki National Aerospace Centre, where advanced cloud radar and Doppler wind lidar systems characterize cloud structures, offering a vertical and horizontal atmospheric context for the flight data. This multifaceted observational approach leverages both spaceborne and terrestrial platforms, maximizing the scientific yield.
The timing of HALO-South’s deployment is strategically chosen to coincide with the Southern Hemisphere’s transition from winter to spring, a critical period during which atmospheric conditions over the Southern Ocean are particularly conducive to precise aerosol and cloud measurements. The campaign is designed to operate in tandem with the European Space Agency’s EarthCARE satellite, underpinning efforts to validate remote sensing retrievals related to aerosols and clouds from space. Additionally, the mission aligns with the EU’s CleanCloud project, expanding efforts to decode the complex interplay between aerosols and climatic phenomena in an era of rapidly changing global emissions.
HALO-South is not a solitary venture but the first of a series of deeply integrated investigations into Southern Hemisphere atmospheric dynamics. Its findings will feed into the goSouth-2 campaign, running from 2025 to 2027, which focuses on ground-based observations contrasting the impact of pristine Antarctic air masses and aerosol-laden air influenced by Australian sources. This comprehensive data set will subsequently inform the large-scale international Antarctica InSync project planned between 2027 and 2030, encompassing a suite of Antarctic expeditions that aim to deepen understanding of polar atmospheric processes in a warming world.
At its core, HALO-South seeks to unravel the complexities of how aerosols influence cloud formation and evolution, and, reciprocally, how clouds modulate aerosol life cycles and distributions. Understanding these interdependencies is pivotal as clouds govern the Earth’s energy balance through their reflection and absorption of solar radiation and their influence on longwave radiation emitted by the planet. The nuanced interactions probed by HALO-South are fundamental to enhancing weather forecasting accuracy and improving the fidelity of climate projections, especially in the Southern Hemisphere where modeling deficiencies have persisted.
This monumental effort is underpinned by the HALO research aircraft itself—a collaborative initiative involving German federal agencies, research societies, and academic institutions. The aircraft embodies decades of technological innovation and expertise in environmental research aviation. It is uniquely equipped to operate in challenging atmospheric conditions and is continuously upgraded to accommodate novel instrumentation, ensuring that it remains at the forefront of atmospheric science missions worldwide. The German Aerospace Center (DLR) not only owns and operates HALO but also fosters its broad scientific utility, collaborating internationally to leverage its capabilities for global climate research.
In conclusion, the HALO-South mission epitomizes the fusion of cutting-edge airborne technology, international scientific collaboration, and targeted research ambitions aimed at resolving critical uncertainties in atmospheric science. By penetrating a hitherto underexplored region that bridges the remote Southern Ocean and the South Pacific, HALO-South promises transformative insights into how clouds and aerosols interact within a low-emission environment. These insights will have far-reaching implications, not only enhancing our ability to simulate and predict climate behavior in the Southern Hemisphere but also informing our understanding of future atmospheric changes in a decarbonized global system. As the world edges closer to ambitious climate targets, the data and discoveries from HALO-South will undoubtedly become cornerstones of atmospheric science and climate policy.
Subject of Research: Not applicable
Image Credits: Roger Riedel, DLR
Keywords: HALO research aircraft, atmospheric science, aerosols, clouds, Southern Ocean, Southern Hemisphere, climate models, aerosol-cloud interaction, radiation budget, airborne measurements, German Aerospace Center, meteorology
