Christchurch launches HALO-South climate research mission

Why scientists flew to the edge of the world – and took off from Christchurch

The HALO-South campaign brought international scientists to Ōtautahi Christchurch to study how aerosols, clouds, rain, and climate behave in the Southern Hemisphere. Flying from Christchurch over the Southern Ocean, the project combined global and local research and aviation expertise – highlighting the city’s role as a collaborative gateway for world-leading atmospheric science.

How HALO-South is helping us understand what lies above

Clouds are something everyone recognises. They drift overhead, familiar and comforting, part of the daily background of life. But despite their ordinariness, they remain one of the least understood pieces of the climate puzzle – and one of the most important.

Why some bring rain and others don’t. Why some are dark, others bright. Why rainfall patterns have become less predictable. “At its core, HALO is about rain,” explains Professor Dr Mira Pöhlker, a leading atmospheric scientist from Leipzig University and the Leibniz Institute for Tropospheric Research (TROPOS). More specifically, how rainfall might behave over entire seasons and decades. “That understanding matters as societies prepare for a more variable and uncertain climate.”

Pöhlker leads HALO-South – an ambitious international atmospheric research campaign that took flight from Christchurch Airport near the end of 2025, heading deep into the Southern Ocean and towards the edge of Antarctica.

Christchurch: a gateway city at the centre of global science

HALO-South didn’t arrive in Christchurch by accident. The campaign is part of a much larger, long-term scientific effort called GoSouth II, which places the city at the centre of Southern Hemisphere climate research.

“It’s a collaborative programme involving a large group of German researchers working closely with New Zealand partners,” explains Professor Adrian McDonald, Associate Head of the School of Physical & Chemical Sciences at Te Whare Wānanga o Waitaha | University of Canterbury and New Zealand’s Principal Investigator for the HALO-South campaign.

HALO-South – the airborne campaign – is one piece of the wider plan. Another is ACADIA, a ground-based measurement programme operating from Tāwhaki National Aerospace Centre near Christchurch and the MetService site in Invercargill for the next 18 months. A future phase, ACAROA, will see the German research vessel RV Sonne sail from Lyttelton Harbour into the Southern Ocean in 2028.

“The overall aim of all these projects is to improve our understanding of aerosols and clouds in the Southern Hemisphere,” McDonald says.

That aim addresses one of the most stubborn weaknesses in modern climate science.

“One of the biggest sources of uncertainty in climate models is how clouds form and how they affect the climate system,” he says. “At the moment, climate models often produce too many or too few clouds over the Southern Ocean compared with reality.”

Those errors ripple outward, affecting sea-surface temperatures, circulation patterns, rainfall and long-term climate projections – not just locally, but globally.

Why the Southern Ocean matters for global science

The answers lie in particles so small they are invisible to the human eye. Known as aerosols, they help clouds form and influence whether they rain, reflect sunlight, or trap heat.

“All of this depends on very complex relationships between clouds and the tiny particles that form them,” Pöhlker explains. “It’s important for the whole climate system, which matters for everyone in the world.”

Some aerosols are natural – sea salt, pollen, dust, even volcanic emissions. Others are human-made, produced by burning fossil fuels. Untangling the difference between the two is vital knowledge – which makes the Southern Ocean so valuable.

“In this region, it’s like a time machine,” Pöhlker says. “It is like going back to a time before human beings, to understand what is natural and what is caused by us.”

Encircling Antarctica, the Southern Ocean is one of the cleanest and least studied atmospheric regions on Earth. Unlike the Northern Hemisphere, where air masses routinely pass over continents and polluted cities, air in the far south circulates vast distances without touching land at all.

“That isolation makes the region incredibly valuable scientifically,” says McDonald. “There’s much less aerosol, dust, and pollution in the air, but most climate models are still heavily informed by Northern Hemisphere data, simply because that’s where most measurements have been made.”

HALO-South was designed to help correct that imbalance.

“Providing high-quality Southern Hemisphere observations can genuinely improve how these models perform for Aotearoa,” he says.

HALO - the aircraft behind the research

Studying these processes isn’t possible from satellites alone. Scientists need to fly directly through clouds, over open ocean, and right to the edge of Antarctic sea ice.

Enter HALO (High Altitude Long Range Observatory). It’s a modified Gulfstream G5 which can fly up to 15 kilometres high, remain airborne for up to 10 hours, and cover distances of around 10,000 kilometres in a single flight. It carries a unique suite of instruments, some normally confined to laboratories, mounted far enough forward to avoid contamination from the aircraft itself.

“That is very unique,” Pöhlker explains. “It means the measurements are extremely clean.”

Why Christchurch was the perfect launch point for HALO-South

For HALO-South to succeed, it needed a base that could support complex science, demanding logistics, and rapid operational decision-making. Christchurch turned out to be ideal.

“It was more or less the best location globally,” Pöhlker says.

Christchurch offers rare access to pristine Southern Ocean air, deep Antarctic logistics experience, and integrated aviation and research infrastructure. That combination allowed the campaign to operate faster, fly further south, and stay flexible as weather windows shifted.

From Christchurch, HALO could sample pristine Antarctic air, then fly into polluted air masses arriving from Australia – a contrast that wasn’t even part of the original plan but proved scientifically invaluable.

The city’s infrastructure sealed the decision. For starters:

“The hangar (GCH Aviation at Christchurch Airport) was the best our team have ever used,” Pöhlker says. “There will be no other airport in New Zealand for them – it was so perfect.”

For McDonald, Christchurch’s strength runs deeper than facilities alone.

Although HALO-South was the first airborne campaign of this scale to operate from Christchurch, many of the city’s partners were already accustomed to supporting Antarctic science.

“Organisations like GCH Aviation already have years of experience supporting Antarctic logistics,” McDonald says. “That means they understand what scientists need, and that made a huge difference.”

Why Tāwhaki was crucial to HALO-South

An important part of the wider campaign took place from Tāwhaki National Aerospace Centre at Kaitorete Spit, south of Christchurch.

“There was also a strong ground-based component,” explains McDonald. “On every day that HALO flew, we launched two or three weather balloons from Tāwhaki to provide additional, supporting measurements. That required a dedicated team of University of Canterbury students and staff, because everything can change at short notice. If the weather shifts, a Tuesday flight might suddenly become a Wednesday flight.”

Situated on the Canterbury coast and away from major population centres, Tāwhaki offered clear skies, open airspace, and proximity to the Southern Ocean – conditions that are difficult to replicate elsewhere.

“The Tāwhaki National Aerospace Centre is in a fantastic location to collect data that is a critical enabler for both aerospace and climatology,” Tāwhaki Aerospace Project Manager John Mann says.

“The combination of our coastal location, away from major populations, with clear skies and proximity to the Southern Ocean mean we can capture data about these unique climate systems and feed it directly into better weather forecasting and climate research,” Mann says, “strengthening our connection with the taiao (environment) by understanding rangi (the sky).”

How local knowledge was crucial for HALO-South

HALO-South flights were expensive, complex, and highly weather-dependent. Each flight represented a major investment – and a limited opportunity to capture rare atmospheric conditions.

“Every flight is a costly effort,” McDonald says. “Roughly half a million dollars per flight.”

Deciding when to fly – and when not to – was critical.

For McDonald, there was an early moment when the value of local expertise became unmistakably clear.

“For the second science flight, there was a discussion about whether we should make measurements near Invercargill or go further south,” he says. “I had written a science paper a few years earlier on this region, and I remember saying, look, it really looks like we should try to go further south, because this weather event is pretty rare.”

Based on his previous work, McDonald estimated only a seven or eight percent chance of such an event occurring at that time of year.

“So it really was a rare opportunity,” he says.

The decision paid off. From that point on, local forecasting knowledge, machine-learning tools developed at the University of Canterbury, and constant coordination with German colleagues shaped the campaign’s success.

Christchurch - an ecosystem built on collaboration

That collaboration extended well beyond the university.

Christchurch’s aviation and operational partners – including GCH Aviation, air traffic control, MetService teams operating in Invercargill and at Tāwhaki, and the Christchurch Antarctic Office – worked together in ways Pöhlker describes as unusually seamless.

“What impressed me most was how experienced and knowledgeable the Christchurch ecosystem was, and how genuinely engaged everyone felt.”

“GCH Aviation was excellent. They made everything smooth and perfect,” she says. “They did the normal things – but at a level that is not normal.”

For HALO-South, that support went well beyond standard aircraft handling. GCH Aviation’s Jet Centre became a self-contained operational base for the mission – a place where flight crews, engineers, and scientists worked side by side throughout the deployment.

The hangar was reconfigured to function as a temporary headquarters, with dedicated briefing rooms, workspaces, and communications set up on site. Operating from a single secure location meant flight planning, data analysis, and operational decisions could happen quickly, often in real time, and without the delays that come from working across multiple sites.

With 24-hour access and direct airside connectivity, the setup allowed the HALO team to arrive, depart, and adapt to changing conditions at any hour – a critical requirement for a campaign where weather windows, airspace availability, and scientific opportunity had to align precisely.

What stood out to Pöhlker was the broader culture underpinning that support.

How HALO-South is changing how we predict weather

The goals of HALO-South are simple to state, even if difficult to achieve: better predictions of rainfall and extreme weather.

“My hope is that our work will contribute to a future where, at the beginning of a season, farmers can be told how the rain is likely to behave over the next six months,” says Pöhlker.

McDonald frames the importance closer to home.

“By collecting these measurements here – effectively right on our doorstep – we’re improving the models in the place where they matter most for New Zealand,” he says.

As climate change brings more droughts and heavier rainfall, both scientists believe the ability to anticipate extremes will matter as much as understanding them.

“We can handle an extreme future much better if we can predict it,” Pöhlker says.

Christchurch - the perfect host for global science

For a campaign as technically demanding as HALO-South, success was never just about the aircraft or the science onboard. It depended on whether Christchurch could support an operation that combined aviation, logistics, international collaboration, and cutting-edge research.

According to Professor Dr Mira Pöhlker, Christchurch delivered that support in ways that surprised even seasoned researchers. Beyond the excellent support and facilities at GCH Aviation and the University of Canterbury, she points to the wider ecosystem that made the campaign work, including Tāwhaki National Aerospace Centre south of the city.

Originally planned as a short six-week deployment, some ground-based measurements at Tāwhaki have been extended for months after the HALO flights ended – a decision driven by the scientific value of the site and the ease of operating there.

That combination of capability and flexibility is not lost on international partners.

One of the clearest demonstrations came in the scale of the HALO-South flight programme itself. Compared with previous airborne campaigns elsewhere, the flights covered a much larger area, reaching further south and sampling a wider range of atmospheric conditions – with Christchurch effectively at the centre.

“That level of coverage is a massive advantage to the international airborne measurement community,” says Professor Adrian McDonald, who led New Zealand’s contribution to the campaign. “It’s concrete proof that Christchurch can enable much more ambitious science.”

For McDonald, the implications extend beyond a single project.

“If we can attract more of these campaigns to New Zealand,” he says, “that’s a win for New Zealand, a win for the science, and a win for Christchurch economically.”

HALO-South shows Christchurch can host complex, high-value global science – and act as a platform for future airborne, polar and aerospace campaigns. Find out more about the Christchurch Gateway to Antarctica.