By Guy Coulson
I recently attended the first data meeting of the goSouth programme, held at the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig. Which seems like a good opportunity for an update on progress of the programme.
Members of the goSouth team Birgit Wehner, Frank Stratmann and me with our poster at the conference.
goSouth is an umbrella name for a number of activities investigating Southern Ocean aerosol-cloud interactions. Associated projects are called goSouth 1, HALO South, ACAROA and ACADIA. It is an international collaboration between TROPOS, the University of Leipzig, the Leibniz University of Hannover, the German aerospace research agency (DLR), the University of Canterbury, the University of Auckland, MetService and The Air Quality Collective. Here I’ll give a quick update on the HALO South and ACADIA-goSouth2 parts of the programme.
Whilst I was in Leipzig, I also attended the START Aerosol Conference run by the German Aerosol Research Association (https://www.info.gaef.de/start2026).
Clouds over the Southern Ocean are a large source of error in the current generation of climate models. Satellite observations show that they are regularly underestimated in models, resulting in errors in sea surface temperatures, that translate into changes in circulation patterns, hampering our ability to predict storm tracks and atmospheric rivers over Aotearoa New Zealand. This is partly due to an incomplete picture of Southern Ocean cloud properties (e.g. droplet sizes, phase state) and the factors (aerosol particles, boundary layer dynamics, atmospheric and cloud turbulence) that influence them.
HALO South has a formal title of “The interplay of Clouds, Aerosols and Radiation above the Southern Ocean”. It aims to investigate the interactions of gas phase chemistry, aerosol nucleation and growth, cloud formation and development, and radiative impacts in the southern Hemisphere North and South of New Zealand using the German High Altitude Long-range Observatory (HALO) research aircraft (HALO (High Altitude and Long Range Research Aircraft). HALO visited Aotearoa in September and October last year. Based in Christchurch the project carried out 21 research flights over the oceans around NZ. The aircraft is packed with instrumentation to measure chemical and physical properties of the atmosphere. The project involved members from universities and research institutes around Germany along with aircraft crew. During the flights, the aircraft reached around 60°S, the furthest south such a research flight has ventured and also flew through an atmospheric river as it crossed Aotearoa – the first time this has been done.
The data meeting took place at TROPOS over three days in April and gathered together around forty people from the numerous institutions that took part in the flights – including three representatives from Aotearoa, Alex Schuddeboom and Daniel Morrish from the University of Canterbury and me. A day and a half of talks covered everything from airborne aerosol physics and chemistry measurements and characterisation to cloud microphysics and trace gasses. I chaired a session on the ground-based measurements from ACADIA-goSouth2 made during HALO overpasses of Invercargill and Tāwhaki. The talks were followed by a day of intensive planning for turning the data into papers – rest assured, there will be rather a lot of them.
goSouth2-ACADIA
One potential mechanism for filling in the gap between observation and modelling is aerosol particles generated by oceanic physical and biological processes being carried aloft to become cloud nuclei. The mechanism is reasonably well understood but its magnitude largely unknown due to a distinct lack of any data from the southern hemisphere. In November 2022, a pilot campaign (goSouth 1) was carried out approximately 50 km west of Invercargill. The pilot study confirmed the southern coast of NZ as a suitable platform for long term measurements of southern hemisphere aerosol-cloud interactions. It also found evidence of new particle formation, provisionally attributed to a combination of marine sulphate and biological terrestrial precursors from the Southern Alps.
Snapshots of goSouth1 at Te Waiwai Bay in November 2022.
The success of the pilot led to a second phase at Invercargill Airport (goSouth 2), which began in October 2025 and will run through to March 2027. A simultaneous ground measurement campaign (ACADIA) is taking place at Tāwhaki National Aerospace Centre just south of Banks Peninsular. Focusing on the vertical distribution of aerosol properties, turbulence and meteorological variables in the marine boundary layer, the aim is to follow aerosol particles rising from formation at sea level to cloud height where they can act as cloud condensation nuclei (CCN) or ice nucleating particles (INP).
The TROPOS LACROS Aerosol and Cloud Remote Observations System (https://www.tropos.de/en/research/projects-infrastructures-technology/coordinated-observations-and-networks/lacros/) has been installed at the MetService office near Invercargill airport along with ground level aerosol measurements (Particle number concentration, particle size distribution, ice nucleating particles and cloud condensation nuclei). Similar instruments are being operated at the Tāwhaki National Aerospace Centre by the University of Canterbury and The Air Quality Collective. The measurement campaigns will run for another year and will compare aerosol and cloud formation in clean air from the Southern Ocean with more polluted air from across the Tasman.
Instruments at Invercargill and Tāwhaki for the goSouth2 and ACADIA ocean-aerosol-cloud interaction measurement campaigns.
Preliminary results from the goSouth2 measurements suggest that aerosol concentrations in the free troposphere are low and can usually be attributed to wildfires in Australia or Africa. Ice formation in clouds warmer than -4°C is frequently absent, suggesting low concentrations of efficient INPs.
As the project progresses, we’ll keep you posted on developments.
goSouth is funded by German Federal Ministry for Education and Research, TROPOS and NZ Ministry for Business Innovation and Employment
