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Hannah Kessenich busts ozone hole myths

Wed, 16 Sep 2026 00:00:00 +1200

The University of Otago marked World Ozone Day by asking Hannah Kessenich to take apart some common myths about the ozone hole. She dispatched three of them in a single sentence.

Three facts that would surprise most New Zealanders

The hole is not above us. It sits over Antarctica and the surrounding ocean. Its edge grazes New Zealand occasionally, maybe one or two days a year, and that is all.

It is not open year-round. It opens for roughly three months each spring, inside the polar vortex, and closes again.

It is not why we burn. New Zealanders face high UV because the Earth’s orbit brings the Southern Hemisphere slightly closer to the sun in our summer, and because our air is unusually clean. Both would be true with no ozone hole at all.

A fourth, less comfortable point: the hole is mostly a natural phenomenon. Stratospheric winds and extreme cold over the pole account for the majority of it. Humans supplied the final ingredient by emitting chlorofluorocarbons, causing the hole to open.

Why this is Tuwhiri’s problem too

The interview ends on something that will be familiar to anyone following this programme. Asked about her research plans, Hannah mentions a paper in review proposing a way to classify ozone hole severity — closely related to the in May — and then mentions, almost in passing, that she is helping build a new instrument meant to take over from a NASA satellite.

That project is Tuwhiri.

Two of her observations explain why the instrument matters. The ozone hole has been lasting longer in recent years than in any previous decade, and nobody yet knows whether that is a signature of climate change. And current projections have it continuing to open until around 2090 — projections which, she notes, do not fully reproduce what is already being observed.

Both are questions you can only answer by continuing to observe the atmosphere. Aura’s Microwave Limb Sounder, the instrument that has watched the Antarctic stratosphere through the polar winter for two decades, will run out of fuel with no replacement planned. Tuwhiri exists to build one small and cheap enough that a country of New Zealand’s size can afford to fly it.

The other reason the hole matters

While the hole is open it creates a pocket of cold air over the South Pole that shifts circulation bands across the whole Southern Hemisphere — changing where winds strike New Zealand, how much rain they carry, and whether a summer brings drought or fire.

Hannah points to the October winds that brought trees down on the Otago campus in 2025. This was in part the work of cold air being pushed north following an ozone hole destabilizing event.

How she got here

Hannah came to Otago from the United States following a physics degree and a job in the technology sector. I thought the ozone hole was old news and a solved problem. It turns out to have many unanswered questions., she says of the field. She went on to join under Annika Seppälä, who now leads Tuwhiri’s atmospheric science. Those unanswered questions became her PhD. She completed it last year and is now a postdoctoral fellow in the Department of Physics.

Minister Penny Simmonds visits the photonics laboratory

Tue, 11 Aug 2026 00:00:00 +1200

Hon Penny Simmonds, Minister of Science, Innovation and Technology and Minister for Tertiary Education, visited the Tuwhiri photonics laboratory at the University of Otago on 11 August 2026.

The visit follows one by her predecessor, Dr Shane Reti, in December 2025, which means both ministers holding the science portfolio during the programme’s first year have now seen the instrument development first hand.

The timing was useful. The programme’s kick-off meeting three weeks earlier had brought the atmospheric science, photonics and engineering teams together to settle what the instrument must achieve, so there was a clearer story to tell than there would have been in the first months of the programme.

JPL meetings and an invited talk in Long Beach

Mon, 27 Jul 2026 00:00:00 +1200

Harald Schwefel visited NASA’s Jet Propulsion Laboratory in Pasadena on 27 July 2026, meeting Andrey Matsko, Subash Khanal and Luis Millán.

JPL matters to Tuwhiri twice over. It is the home of the Aura Microwave Limb Sounder whose record the programme exists to continue, and it is where several of our advisors work on the resonator physics the instrument depends on. Sitting down with people who have operated a limb sounder for two decades is the fastest way to learn which problems are real and which only look hard from the outside.

Subash Khanal is co-applicant on the that formalises this collaboration, so the visit also allowed time for working on that.

The visit coincided with the Optica Advanced Photonics Congress in Long Beach, California, where Harald gave an invited talk at the Nonlinear Photonics topical meeting. Nonlinear Photonics covers exactly the ground the instrument occupies — nonlinear optical materials, frequency conversion and resonator systems — and it is one of the better venues for putting the up-conversion approach in front of the community that would recognise its limits.

Otago Daily Times: clock ticking on bid to replace important weather satellite

Tue, 21 Jul 2026 00:00:00 +1200

The Otago Daily Times reported on Tuwhiri during the programme’s kick-off meeting, under the headline Clock ticking on bid to replace important weather satellite.

The headline gets the problem right. NASA’s Aura satellite has been measuring ozone and related gases for more than two decades, and its Microwave Limb Sounder is the only instrument capable of watching the Antarctic stratosphere through the polar winter, when the ozone hole forms. Aura will run out of fuel, and no replacement mission is planned — conventional instruments of that kind cost more than anyone is currently willing to spend.

The meeting the article covers, held at the University of Otago from 19 to 21 July 2026, brought the whole programme team together for the first time and was the occasion on which the name Tuwhiri was presented publicly.

Coverage in the regional paper matters more than its circulation suggests. Much of what Tuwhiri is building will be made and flown in New Zealand, and the case for public investment is easier to make when people can read about it somewhere other than a university press release.

Catalyst: Seeding award to build a partnership with NASA JPL

Wed, 01 Jul 2026 00:00:00 +1200

A Catalyst: Seeding project, Bridging CMOS and Photonic Spectroscopy for Stratospheric Water Vapour Measurements, establishes a formal research collaboration between the University of Otago and NASA’s Jet Propulsion Laboratory.

Harald Schwefel is principal investigator, with Dr Subash Khanal of NASA JPL as co-applicant. Annika Seppälä leads the atmospheric science, Mallika Suresh the photonic science, and Randy Pollock the systems engineering. On the JPL side the project also draws on Dr Adrian Tang, who directs JPL’s Space System-on-Chip programme, and Dr Nathaniel Livesey, who led the Aura Microwave Limb Sounder for nearly two decades and sits on Tuwhiri’s advisory board.

Catalyst:Seeding is administered by the Royal Society Te Apārangi on behalf of MBIE. It funds the building of international research relationships rather than the research those relationships go on to produce, which is exactly what is needed here.

Why water vapour

Tuwhiri’s instrument was conceived for ozone. Water vapour is a natural second target: the most abundant greenhouse gas in the atmosphere, closely tied to atmospheric circulation, extreme weather and ozone recovery — and poorly observed in the stratosphere, particularly in the Southern Hemisphere.

The Hunga Tonga–Hunga Haʻapai eruption made the gap plain. It injected an unprecedented quantity of water vapour into the stratosphere, and the observing system was not well placed to track what followed.

Ozone and water vapour sensing share their physical principles but differ in frequency and in what calibration demands. Extending the photonic approach from one to the other is a real piece of work, not a relabelling.

Benchmarking against a proven instrument

Laboratory validation only takes a millimetre-wave spectrometer so far. At some point it has to be measured against an instrument whose behaviour is already understood.

JPL has a compact, flight-proven CMOS spectrometer operating at the 183 GHz water line. The project’s aim over two years is technical alignment — workshops, research exchanges and joint engineering studies — working towards flying the two sensors side by side on a Kea Aerospace Kea Atmos stratospheric aircraft. Measuring the same air at the same moment with a new instrument and an established one is the most credible way to find out what the new one can actually do.

That is a rare opportunity. It also reduces the risk carried by everything Tuwhiri builds afterwards.

Tuwhiri at the EGU General Assembly in Vienna

Fri, 08 May 2026 00:00:00 +1200

Florian Sedlmeir and Hannah Kessenich presented Tuwhiri’s work at the European Geosciences Union General Assembly, held in Vienna from 3 to 8 May 2026.

Florian presented , the instrument side of the programme — how a whispering-gallery-mode resonator converts faint atmospheric signal into optical light that ordinary photonics can measure.

Hannah presented , which addresses the other end of the problem: what you do with the measurements once you have them, and how to describe the behaviour of the ozone hole in terms that a forecasting model can use.

The EGU General Assembly is the largest geosciences meeting in Europe, drawing around 20,000 researchers across the Earth, planetary and space sciences. For a programme that sits between instrument development and atmospheric science, it is a useful place to be heard by both communities at once — and to test whether the case for a low-cost limb sounder lands with the people who would use the data.

Minister Shane Reti visits the photonics laboratory

Wed, 10 Dec 2025 00:00:00 +1300

Dr Shane Reti, then Minister of Science, Innovation and Technology, visited the photonics laboratory at the University of Otago in December 2025.

The visit was a chance to show, rather than describe, what the programme is building: the whispering-gallery-mode resonators at the heart of the instrument, and the up-conversion experiment that turns faint microwave and terahertz signals from the atmosphere into optical light a compact detector can measure.

The argument Tuwhiri makes is partly an economic one — that an instrument small and cheap enough to fly on a CubeSat changes what a country of New Zealand’s size can afford to monitor from space. That case is easier to make standing next to the apparatus.

Dodd-Walls Centre annual symposium

Mon, 24 Nov 2025 00:00:00 +1300

Mallika Suresh took part in the Dodd-Walls Centre annual symposium, held from 24 to 27 November 2025.

The Dodd-Walls Centre is New Zealand’s Centre of Research Excellence for Photonic and Quantum Technologies, and one of Tuwhiri’s affiliated partners. Its annual symposium puts most of the country’s photonics community in one room, which makes it the natural place to present the up-conversion work and to meet the students the programme will need over the next five years.

Learning how Antarctic campaigns are run

Thu, 20 Nov 2025 00:00:00 +1300

Programme Lead Harald Schwefel spent part of November 2025 in Antarctica, working alongside of the University of Otago on her sea ice research.

The scientific contribution was one reason for going. The other was reconnaissance. Tuwhiri intends to fly its radiometer on balloons from Antarctica, and a polar deployment is unlike any other kind of fieldwork: the logistics chain, the weather windows, the constraints on what can be carried and what can be repaired on site all shape the instrument long before it is built.

Understanding how an Antarctic campaign is actually organised — how far ahead decisions must be made, what support exists on the ice, and where things typically go wrong — is the sort of knowledge that does not transfer from reading about it. Bringing it back into the engineering team’s planning is worth more than the time it cost.