Atmospheric-Science |

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.

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.

A novel diagnostic metric for quantifying Antarctic ozone hole dynamics

Sat, 14 Mar 2026 00:00:00 +1300

Millimeter-Wave Atmospheric Radiometry via Nonlinear Optical Upconversion

Sat, 14 Mar 2026 00:00:00 +1300

Quantifying the contribution of transport to Antarctic springtime ozone column variability

Wed, 03 Dec 2025 00:00:00 +1300

Tuwhiri Programme Kick-off Meeting

Mon, 01 Jan 0001 00:00:00 +0000

The occasion

Everyone in the programme in one place for the first time: three research areas, the advisory board, industry partners, and colleagues from Adelaide, Caltech, Earth Sciences New Zealand, Waikato, AUT and the Paihau–Robinson Research Institute.

The welcome function opened with a mihi whakatau, followed by a welcome from Programme Lead Professor Harald Schwefel. Jessa Barder then presented the programme’s new name — Tuwhiri, from the Māori word meaning a clue, or means of discovering something hidden, which is an appropriate metaphor for what an atmospheric sounder does, as well as to reveal or make known, which is an accurate description of the programme’s goals.

Sunday 19 July — Welcome function

Terrace Lounge, University Union Building.

Mihi whakatau, the welcome from the Programme Lead, the presentation of the programme name, and guided tours of the research laboratories.

Monday 20 July — Setting out the problem

Walsh Building.

The morning established why the work matters and where each area currently stands. Annika Seppälä opened on the case for space-based climate and atmosphere monitoring. Mallika Suresh followed on dielectric resonators for nonlinear optical upconversion of microwave signals, and Randy Pollock set out the engineering team’s staffing, status and open questions.

The second session widened the frame: Peter Gibson on climate change projections for New Zealand from CMIP6, Andrey Matsko on microphotonics for spaceborne timing and remote sensing, and Withawat Withayachumnankul on terahertz technology from devices through to sensing and communications.

The afternoon split in two. One workshop took on sensor, platform and data systems integration, chaired by Betina Pavri and Mallika Suresh; the other planned the atmospheric science model simulations, chaired by Annika Seppälä.

The day closed with Jessa Barder on plans for community engagement, a contribution from Richard Querel, and open discussion.

Tuesday 21 July — From requirements to instrument

Centre for Innovation and Mellor Laboratories.

The morning ran from the science down to the hardware. Hamish Lewis presented late-century projections of climate extremes across New Zealand; Florian Sedlmeir on millimetre-wave atmospheric radiometry via nonlinear optical upconversion; Hannah Kessenich on a new diagnostic metric for quantifying Antarctic ozone hole dynamics; John Cater on thermal and mission design; and Betina Pavri on Kea Mk1 interface requirements and environmental test planning.

Two further workshops ran in parallel. The first brought the atmospheric and engineering teams together on instrument requirements for science, chaired by Randy Pollock — the conversation that decides what the instrument has to achieve. The second, chaired by Greg Bodeker, addressed uptake and impact.

A poster session ran over lunch, and Harald Schwefel closed the meeting.