During the “HALO-South” campaign starting in September, researchers will study the interactions between clouds, aerosols and radiation over the Southern Ocean. For five weeks, HALO will conduct measurement flights from Christchurch over the oceans of the clean Southern Hemisphere. “We hope that the large-scale HALO-South measurement campaign will enable us to make an important contribution to closing this gap,” says campaign leader Professor Mira Pöhlker from TROPOS and Leipzig University. “We are very pleased to have so many experienced experts on board to work together to answer questions such as: what aerosols are present in the Southern Ocean? Where do they come from? How do they change clouds?” The researchers hope the measurements will not only provide valuable data to improve weather forecasts and climate models for the little-studied south, but also a better basic understanding of how the atmosphere and clouds will respond to a decline in emissions over the coming decades. The aircraft measurements during HALO-South will mainly be funded by the German Research Foundation (DFG), with additional support from the Max Planck Institute for Chemistry (MPIC) and the German Aerospace Center (DLR). They mark the beginning of closer research collaborations between Germany and New Zealand.
Clean southern air as a challenge for climate models
Ground-based remote sensing observations provide an important link between the HALO-South flight mission in September and October 2025 and the German research vessel expeditions with Sonne and Polarstern planned for 2027/28. All of these will study the atmosphere of the Southern Ocean at the edge of Antarctica. MetService New Zealand and the University of Canterbury in Christchurch (Ōtautahi) are also key partners in the projects.
The clouds over the southern tip of New Zealand’s South Island are shaped primarily by the ocean, as air masses move north from Antarctica and the Southern Ocean towards New Zealand. Along this route, there are no major continental sources of emissions such as mineral dust, wildfire smoke, or human contributions from heavy industry and traffic. However, episodes of dust-laden and polluted air do occur when air masses travel from Australia, or when wildfire smoke from Africa or even South America is transported at high altitudes. These stark contrasts in air pollution are thought to be one reason why weather and climate models still struggle in this region. Cloud forecasts for the Southern Hemisphere are consistently less reliable than for the Northern Hemisphere – most likely because the cleaner air contains fewer aerosol particles, the tiny nucleation seeds needed for cloud droplets and ice crystals to form.
Seven years of preparation for major measurement campaigns at the edge of the Southern Ocean
Since 2018, preparations have been under way for the major atmospheric research project that will, in the coming months, collect detailed data on aerosols, clouds and precipitation, information urgently needed by the global climate modelling community. The campaign is called goSouth-2 because an initial test campaign, “goSouth”, was already carried out in 2022 in cooperation with the National Institute of Water and Atmospheric Research (NIWA) in New Zealand.
“We scan the distribution and movement of aerosol and cloud particles in the atmosphere above us several times per minute, with a spatial accuracy of a few metres. These observations allow us to distinguish between various components, such as ice crystals, cloud droplets or the different types of aerosols. This provides the basis for all subsequent investigations into interactions between aerosols and clouds,” says Dr Patric Seifert from TROPOS. “Since the radars used also record profiles of precipitation particles, it is possible to investigate the influence of different air masses on rain formation,” says Professor Heike Kalesse-Los from Leipzig University.
The location at the southern tip of the South Island is ideal for characterising the pristine air from Antarctica and the Southern Ocean. Nevertheless, the researchers expect air masses from Australia, which contain more higher levels of aerosol pollution, to occur about 25 per cent of the time. “This contrast will allow us to make detailed comparisons, as initial analysis of long-term lidar measurements from Lauder, New Zealand, has already shown,” says Patric Seifert. The aim of goSouth-2 is to conduct a detailed contrast study of cloud properties in clean Antarctic air compared to clouds in aerosol-polluted Australian air. Such an investigation is key to a better understanding of the possible variability of clouds under changing aerosol conditions. To this end, the team led by Patric Seifert and Heike Kalesse-Los from Leipzig University has received funding from the German Research Foundation (DFG) for the ACADIA project.
Ground measurements by Leipzig University
In addition to their collaboration in the ACADIA project, researchers from Leipzig University will support the HALO-South flight campaign with additional measurements at the Tāwhaki National Aerospace Centre on the eastern side of New Zealand’s South Island over the coming months. The LIMRAD94 cloud radar from Leipzig University was shipped to New Zealand in TROPOS containers. In addition, several radiosondes (weather balloons) will be launched from Tāwhaki on each HALO flight day. The ground measurements at Invercargill Airport (Waihōpai) and the Tāwhaki National Aerospace Centre are also part of the EU CleanCloud project, which investigates the interactions between aerosols and clouds to improve understanding of climate dynamics under changing environmental conditions.
