Halley Dobson Ozone Record: The Two Seasons It Lost

The Dobson spectrophotometer at Halley cannot measure ozone in the dark. It needs the sun, or failing that the moon within about a week of full, and at 75.5 degrees south it gets neither in May, June or July. The famous record it produced — the one that found the ozone hole in 1985 and is almost always described as continuous since 1956 — has a hole of its own in it. Two entire ozone-hole seasons, 2017 and 2018, were never measured, and have been reconstructed from the satellites the instrument is celebrated for having beaten.

Silence Index — D-182

Effectively unvisited

Ranks 23 of 99 scored dossiers — quieter than 78% of the others we have scored. A low score is not a warning; it describes who else will be standing next to you.

How the total is weighted. These are the fixed weights of the four inputs, the same on every dossier — not this place’s scores. We do not publish per-input bars, because the per-input values were never recorded article by article and inventing four plausible numbers that sum to the total would be a fabrication dressed as a chart.

Footfall pressure — visitors measured against the ground that absorbs them30%

Access friction — permits, caps, seasons, boats, weather windows30%

Acoustic floor — how close the nearest engine is20%

Unresolved questions — what the record still cannot settle20%

This dossier was scored before 2 September 2026, when the fourth input became night darkness. It keeps the input it was reasoned with until it is re-scored at its next source re-check; the methodology page records the change.

The index is a desk instrument scored by this publication, not a field measurement. How it is calculated, and where it fails.

What this dossier is built from

Nobody from this publication has been to Antarctica, and there is no route by which we could go. What follows is desk research: the operating manual Halley's observers work from; the British Antarctic Survey's legacy ozone pages, maintained by one of the three authors of the 1985 paper; the BAS Polar Data Centre record for the series; a 2021 paper in Atmospheric Chemistry and Physics by MIT, BAS, Bremen, KNMI and NASA Goddard; NASA's Nimbus-7 TOMS User's Guide and Ozone Watch statistics; NOAA's and Japan's Dobson documentation; the WMO/UNEP assessment; and FCDO permit guidance.

This is not a story about a hole in the sky. It is a story about a machine with three specific limitations, and what happens to a legend when you take them seriously.

The machine, described honestly

A Dobson ozone spectrophotometer is a device for comparing the brightness of two colours of ultraviolet light. Ozone absorbs strongly at the short end of the ultraviolet and barely at all a little further along, so the difference between what left the sun and what reaches the ground is ozone.

The elegant part is how the comparison is made. You do not measure two brightnesses and divide. You slide a calibrated optical wedge into the path of the brighter beam until a rotating sector wheel, flicking between the two beams onto a single photomultiplier tube, produces no alternating signal at all. The microammeter reads zero, and the observer reads a number off a dial — the R-value. That dial position, not the light, is the measurement. It is a null method, so it does not care whether the detector is drifting, the tube is tired, or thin cloud has dimmed both beams equally.

The R-value converts through a calibration table into an N-value, and the ozone amount falls out of an equation with three terms: the difference in N-values, the absorption coefficients for the pair in use, and mu, the ratio of the slant path the light took to a straight vertical one. NOAA's handbook prints a worked example, and the arithmetic is small: 1000 × ((0.968 − 0.319) / (1.388 × 1.339) − 0.008) = 341 Dobson Units. That is a complete total-ozone measurement. There is nothing else in it.

The wavelengths come in lettered pairs, and here we hit a disagreement between two authoritative sources. The BAS Dobson manual, as we read it, gives A as 305.5 and 325.4 nanometres, C as 311.4 and 325.4, D as 317.5 and 325.4. The Japan Meteorological Agency, describing the identical instrument, gives A as 305.5 and 325.0, C as 311.5 and 332.4, D as 317.5 and 339.9. We have not resolved that, and we will not average two sets of physical constants, so both are printed. What both agree on is the trick that makes the instrument credible: take two pairs in one observation and subtract, so that whatever haze or cloud did to the light largely cancels between them. That is the AD double pair, and it underlies essentially every serious number in the world total-ozone archive.

What it measures, and the three things it cannot

What comes out is one number: the total ozone in the entire column of air directly above the instrument, in Dobson Units — one unit being a layer of pure ozone a hundredth of a millimetre thick at zero degrees and one atmosphere, about 2.69 × 10^16 molecules per square centimetre. A normal sky is around 300 DU.

Three limitations follow. They are not defects; they are the shape of the thing.

No height. The column total says nothing about where in the column the ozone sits. A Dobson can be coaxed into a crude vertical profile by the Umkehr method, watching how the zenith-sky ratio turns over as the sun sets, but that is a slow inversion of a weak signal and not what the station does day to day.
No width. A direct-sun observation looks at the sun. A zenith observation needs about a ten-degree cone of clear sky overhead. The Dobson knows about the air over Halley and nothing whatever about the air fifty kilometres away.
No dark. It is a photometer. Without a light source there is no measurement.

The last is the interesting one, because at Halley it is seasonal and total. The BAS ozone pages state the observing season plainly: it normally begins at the end of August and ends in mid-April. The 2021 paper puts the negative case just as plainly — no routine ozone data are available at Halley in May, June and July, when the sun is below the horizon. There is a partial workaround: the manual describes focused-moon observations, usable about seven days either side of full moon, and BAS confirms that some lunar measurements exist outside the seasonal blocks but are not in the standard files. A few nights a month, in an archive built on daily values, is not a winter record.

Even the shoulders are soft. The manual allows direct sun only out to mu of about 2.8 and zenith blue sky to 2.6, and BAS says the quiet part out loud: measurements at the start of the season are less accurate than in midsummer, because the sun is so low.

What popular coverage gets wrong

The story almost everybody knows runs like this. NASA's Nimbus-7 satellite had been watching Antarctic ozone since 1978 and had seen the hole years before anyone else. But its processing software had been told that readings below some threshold were impossible, so it threw them away as errors. Three British scientists with an old brass instrument found it instead, using sunlight and a dial. Moral: never let a computer discard your outliers.

It circulates hardest in statistics teaching rather than in travel writing. The earliest dated instance we could find is the RISKS Digest of 1 August 1986, where a contributor named Bill McGarry asks why the satellite failed to report the hole and answers himself: "Because it had been programmed to reject values that fell outside the 'normal' range!" Forty years later it is on the University of Melbourne's Statistical Consulting Centre guidance for students, as the claim that "Antarctic satellite collection data systems automatically deleted outliers, and as a result the hole in the ozone layer was detected much later than it could have been". A University of Arizona lecture teaches that TOMS detected the developing hole "but the anomalously low readings were rejected as 'noise' by the computer program set up to process the data".

Now the record. NASA's own Nimbus-7 TOMS User's Guide describes the data architecture, and it does not contain a delete step. Retrievals carry a quality flag, and for the daily gridded Level-3 product "only the data with quality flag values of 0 are used to compute the averages". Excluded from an average is not the same as destroyed, and the difference turns out to be the whole story. Erik Conway, the historian at NASA's Jet Propulsion Laboratory, told Nature in 2019 that the Goddard team had set quality-control software to "mark as potentially bad data anything that showed levels below a certain amount" — and then the punchline: "when the Goddard folks mapped all these flags of potentially bad data, they were all over the Antarctic, exactly where the British Antarctic Survey said it should be." The flags themselves drew the hole. You cannot map data you have deleted. The Goddard confirmation reached print in Nature on 28 August 1986, reporting a 40% fall in the ozone minimum between 1979 and 1985.

There is a second and sharper account, and we will attribute it rather than adopt it. Jonathan Shanklin, one of the three authors of the 1985 paper, wrote in Nature in 2010 that his team had been making ground measurements timed to satellite overpasses and sending them to the Satellite Ozone Analysis Center at Livermore in California. He wrote to the head of the centre asking whether the satellites confirmed some low ozone values. "I never received a reply — perhaps another lucky break for our team." And on why the satellite people were not seeing what he was seeing: one of their goals was latitudinal variation, "which probably involved averaging ozone values around a latitude circle. This sort of analysis would have effectively hidden the ozone hole, because of its offset from the pole."

That is a participant's recollection, written twenty-five years after the events, using the word "probably" about somebody else's method. We print it as Shanklin's account, not as settled history. But note what it claims and what it does not. It does not claim anybody deleted anything. It claims the processing geometry was wrong for the shape of the object — a lopsided hole, smeared flat by averaging around the wrong kind of ring. The contemporary NASA literature fits that reading rather than the legend: a 1989 Goddard error analysis by Bhartia, Krueger and colleagues says the conditions inside the hole "were not anticipated in the design" of the retrieval algorithm.

The advantage the Dobson actually had

Strip the legend away and the British team's real edge becomes visible, and it is a better story than the one it replaced. It was not sensitivity, and it was not sunlight versus software. It was the length of the baseline. Nimbus-7 launched on 24 October 1978 and its archived ozone record starts on 31 October 1978. That is the beginning of the satellite era, and NASA's own hole-definition page notes that total ozone values below 220 Dobson Units were not observed before 1979. A satellite record that begins in 1979 cannot tell you what 1965 looked like. The Halley Dobson record begins on 17 September 1956, and the whole meaning of the 1985 result was that October values had been falling away from a baseline three decades deep. BAS's own summary of the trend is that mean October ozone fell by around 3% a year from 1976, while atmospheric chlorine rose by about 3% a year.

There is a footnote here for anyone inclined to feel superior about automated outlier rejection. When Halley's Dobson produced its first spring values in 1956 they were far lower than theory allowed, and the first suspicion was the instrument. Dobson himself later recalled that the September and October 1956 values "were about 150 units lower than was expected". It took a second year of the same pattern before anyone believed the machine. Human observers reject anomalies too. They just do it more slowly, and with more paperwork.

The chain that makes the number mean anything

A dial reading in Antarctica is worth nothing unless it means the same thing as a dial reading in Hawaii. The network's answer is a physical chain of custody. NOAA holds the World Standard Dobson, D083, at Mauna Loa Observatory — 19.5362°N, 155.5763°W, 3,397 metres — chosen for stable tropical ozone and clean air above the aerosol layer. Regional standards are compared against D083 about every two years and propagate the calibration outward to station instruments, whose precision is held to better than ±1% and checked monthly against a standard lamp.

Two consequences matter. First, that chain is what allows a satellite to be believed: NOAA describes the calibration work as underpinning verification of satellite ozone climate records from both NOAA and NASA. The ground network is the ruler the orbiting instruments are checked against — a rather different relationship from the rivalry the legend imagines. Second, the chain has been re-cut. Absorption coefficients moved from the Vigroux scale to Bass-Paur on 1 January 1992, and the combined effect of new absorption and scattering coefficients was to reduce reported ozone values by 2.6%. BAS's older Halley data, computed with Powell coefficients, was scaled onto the new basis with a WMO-recommended factor of 0.9743. The record is not a stack of raw readings. It is a stack of readings that have been argued about.

The hardware changed too. BAS lists Dobson 103 at Halley from February 1991, Dobson 73 from December 2005 and Dobson 31 from February 2012, with overlaps so the constants could be transferred. We could not establish which instrument was on the roof in 1985, and could not verify the "brass" of the popular retelling either.

The two seasons that are not there

In February 2017 the Halley record stopped, and the cause was not instrumental. Chasm 1, a crack in the Brunt Ice Shelf dormant for roughly thirty-five years, resumed moving in 2012, and in October 2016 the Halloween Crack opened about seventeen kilometres north of the station, across the resupply route. Halley VI is built on skis for this. Its eight modules were towed to a new site in a thirteen-week operation completed on 2 February 2017 — BAS's relocation announcement and its ice-shelf monitoring page both say 23 kilometres, a later BAS release says 32, and we print both because both are BAS's own. The station was then left unoccupied for the winter: a mid-winter evacuation from a shelf that might calve, in the dark, below minus fifty, is not a plan.

The instrument stayed. The observer did not. No ozone was measured at Halley during the austral springs of 2017 or 2018 — the two months of the year the entire record exists for. The 2021 paper's phrasing is unsentimental: that February the station was forced to cease operations because of the structural stability of the shelf, and the continuity of a unique record was broken.

The repair is the part that ought to make anyone who has repeated the legend pause. The gap was filled with satellites. Lily Zhang, Susan Solomon and colleagues, with Shanklin himself among the co-authors, took eleven satellite instruments — GOME, GOME-2A and 2B, SCIAMACHY, SBUV, three generations of TOMS, OMI and the two OMPS sensors — and computed, for each day of the year, the average difference between each satellite and the Dobson across all the years both existed, then applied those offsets across the missing seasons. Tested against withheld Dobson data, the method reproduced monthly ground values to 1.1 ± 6.2 DU for the instruments used across the 2017-18 gap, against 4.6 DU for raw satellite data alone. The residual differences are largest in April and August — exactly where you would predict, at the ends of the season, when the ground instrument is at its worst.

One further wrinkle is an instrument story too. Halley now runs an automated Dobson, housed in a white container and powered by a micro-turbine in a green one, and the 2021 analysis found the provisional 2019 automated data showing substantially larger negative offsets against the satellites than any manual year. The authors excluded 2019 and treated 2020 as likely inconsistent as well. A record that has been the world's yardstick since 1956 has a two-year hole filled by satellite arithmetic, followed by two years the analysts declined to use.

Why the Silence Index is 87

Physical remoteness is at the ceiling: a floating ice shelf at 75.5 degrees south, flowing west at up to two kilometres a year, which shed a 1,270 km² iceberg in February 2021 and a 1,550 km² one in January 2023. Access friction is absolute for anyone not on a national programme, and the FCDO's own wording is that travelling to any part of Antarctica without permission can mean a fine or a prison sentence. Visitor volume is nil — up to fifty-two people in summer, all working. The fourth input we have scored is night darkness, and here Halley is extraordinary: the sun is under the horizon for three solid months, which is why this dossier exists. What keeps it off the nineties is that this is a functioning station with a skiway, a micro-turbine and a satellite link. An instrument shed with a generator is not silence.

What the instrument leaves us with

The ozone layer is recovering. The 2022 WMO/UNEP assessment projects total column ozone returning to 1980 values around 2066 in the Antarctic, around 2045 in the Arctic and around 2040 for the near-global average, and BAS's own Halley analysis finds a slow increase of roughly 1 DU a year in the October minimum since 1994. The Montreal Protocol, signed in 1987 and in force from 1989, did what it was written to do.

But the chain that got us there ran through a machine that cannot see in the dark, cannot see sideways, cannot see height, and until 1992 was reporting numbers 2.6% different from the ones it reports now. It found the hole not because it was better than the satellites but because it was older than them, and because somebody had kept it pointed at the same patch of sky since 1956 for no immediate reason. The satellites did not throw the hole away. They flagged it, and the flags drew its outline across the continent.

The instrument decided what we believe. Not the sky. And when the ice shelf finally made the instrument stop, the record it had built was patched — carefully, publicly, with stated uncertainties, by the people who own it — using the very measurements it is supposed to have outperformed. That is not a humiliation. It is what a mature observing system looks like: two techniques with different blind spots, each covering for the other, and neither of them a hero.

Corner Codex — D-182

Instrument: Dobson ozone spectrophotometer, a 1920s design still the world standard
Station: Halley Research Station, Brunt Ice Shelf, 75.56821°S 25.50852°W (BAS)
Record begins: 17 September 1956, per the BAS Polar Data Centre metadata record
What it measures: Total ozone in the whole column overhead. One number, one point, no height
How: Ratio of two ultraviolet wavelengths, nulled with a calibrated optical wedge
Observing season at Halley: Roughly end of August to mid-April
Blind months: May, June and July — the sun is below the horizon and there is nothing to measure
Calibration chain: Every station instrument traces to World Standard Dobson 83 at Mauna Loa
Instruments at Halley since 1991: Dobson 103, then Dobson 73, then Dobson 31
The gap: No ozone data at all in the austral springs of 2017 and 2018
How the gap was filled: GOME-2, SBUV, OMI and OMPS, adjusted day-by-day against the Dobson
Fill accuracy: 1.1 ± 6.2 DU average difference against the ground instrument
Silence Index: 87 / 100

The Traveler's Panel · checked 25 August 2026

Changing information. Prices, permits, seasons and road access change, sometimes at short notice. Everything here is a starting point for your own confirmation — not a quote, and not a guarantee. Verify with the operator and the relevant official body before you book.

The instrument	Dobson ozone spectrophotometer, a 1920s optical null device
What it returns	One number — total ozone in the column overhead, in Dobson Units
Blind months	May, June, July. No sun, no measurement
Observing season	End of August to mid-April, weakest at both ends
Record starts	17 September 1956
The gap	Austral springs 2017 and 2018, filled from GOME-2, SBUV, OMI and OMPS
Station staffing	Summer only since 2017; up to 52 people, none of them visitors
Permit	FCDO Polar Regions Department. Four months' notice for anything new

Getting there — No public route exists. Access is by British Antarctic Survey air and ship operations only

There is no visitor route to Halley and this panel is not going to invent one. The station sits on a floating ice shelf at 75.56821°S, 25.50852°W, is reached only through British Antarctic Survey air and ship operations, and exists to hold instruments rather than people. If you are not on the programme, the practical answer is that you cannot go.
The legal machinery is worth understanding anyway, because it is the access regime for the whole continent. Anyone on a British expedition to Antarctica, or taking a British vessel or aircraft there, must hold a permit from the Polar Regions Department of the Foreign, Commonwealth and Development Office. The department asks for at least four months for a new or unusual application and two months for a repeat of previously permitted summer activity, and states that late applications may not be considered.
The FCDO's own travel advice puts the consequence in one sentence: travel to any part of Antarctica without permission and you could get a fine or a prison sentence. For organised tourism the operator normally holds the permit; there is no organised tourism to the Brunt Ice Shelf.
Above the permit sits the Protocol on Environmental Protection to the Antarctic Treaty, signed in Madrid on 4 October 1991 and in force since 1998, which designates Antarctica a natural reserve devoted to peace and science. Article 7 bans mineral resource activity other than scientific research. The Protocol has no expiry date, whatever you may have read about 2048.
The physical constraint is separate from the legal one and is currently the binding one. Halley has been unoccupied through the winter since 2017 because a mid-winter evacuation from a shelf with an active chasm system, in the dark, at below minus fifty, is not something BAS is willing to plan for. The instruments run on a micro-turbine and a satellite link instead.

Indicative costs — verify before booking

What it costs	Nobody should be pricing this. There is no lawful way in for a visitor
The permit	No fee is published in the FCDO guidance we opened. It is not a ticket
The real currency	Lead time. Four months minimum for a new British Antarctic application
What the data costs	Nothing. The Halley series is public via BAS and WOUDC
What the gap cost	Two ozone-hole seasons, and a reconstruction with a stated 6.2 DU spread

What to pack

Nothing. This is a place to read rather than to visit, and the reading is free: the BAS legacy ozone pages carry the daily, monthly and minimum data files, the observing manual and the metadata description.
If you want to understand the instrument rather than the story, start with the Dobson manual's observation-type table — direct sun, zenith blue, zenith cloud, focused moon — and note which air-mass range each one is allowed in. The limits are the argument.
A tolerance for uncertainty notation. Almost every number in this field arrives with a plus or minus attached, and stripping it off is how the legends start.
Scepticism about any account of this discovery that has a villain in it, including ours.

Where to stay

Nobody stays at Halley who is not working there, and since 2017 nobody stays through the winter at all. The station is Halley VI, eight interlinked modules on hydraulic legs and skis, occupied in summer by up to fifty-two people and left to run itself for the rest of the year on a micro-turbine, with the automated Dobson in a white container and the electrical and network services in a red one. It is the sixth station of that name on this shelf, and the design brief for the skis is the whole history of the previous five: ice moves, snow buries, and a building that cannot be lifted and towed is a building with an expiry date. In the 2016-17 summer the modules were towed to a new site in a thirteen-week operation finished on 2 February 2017, and the two figures BAS has published for how far they went — 23 kilometres and 32 kilometres — are a fair indication of how precise anything about this place is allowed to be.

Safety & responsible travel

Do not repeat the claim that NASA's software discarded or deleted the low ozone readings. The Nimbus-7 TOMS documentation describes flagged values excluded from gridded averages, and a NASA historian's account in Nature has the flags themselves mapping the hole's outline.
If you teach outlier rejection, teach it with an example you have checked. The ozone hole is the standard cautionary tale in statistics classes and it is, on the documentary record, the wrong one.
Attribute Shanklin's account to Shanklin. His recollection of the unanswered letter and the latitude-circle averaging is first-hand, valuable and hedged by its own author. It is not the same category of evidence as a user's guide or a data file.
Do not describe the Halley record as continuous. It has been broken once, publicly, by an ice shelf, and the people who own it have documented the break and the repair themselves.
If you want to support this kind of measurement, understand what it is: sixty-nine years of somebody reading a dial at a place where nothing happens, funded on the assumption that a baseline is worth having before you know what you will need it for.

Nearby, and quieter

Nothing is nearby in any sense a visitor would recognise. The nearest comparable instruments are hundreds of kilometres of ice and ocean away: Rothera, at 67.568889°S 68.1248°W, operating since October 1975 and running meteorology and ozone monitoring; and Akademik Vernadsky at 65°15'S 64°16'W on the Argentine Islands, which was the British Faraday station and the second data series in the 1985 paper before it was transferred to Ukraine in 1996. Further off, the South Pole Observatory has been measuring since the International Geophysical Year of 1957 at 2,837 metres. And the site that matters most to the meaning of every Halley number is not in the Antarctic at all: it is Mauna Loa Observatory in Hawaii, at 19.5362°N 155.5763°W and 3,397 metres, where the World Standard Dobson D083 sits and against which every other instrument in the network is eventually compared. The Brunt Ice Shelf itself provides the only other landmarks, and they are temporary: Chasm 1, the Halloween Crack, the North Rift, and the icebergs those produced — 1,270 km² in February 2021, 1,550 km² in January 2023.

Getting there, in order

1Akademik Vernadsky (formerly Faraday)
↓
2Halley VI Research Station
↓
3Rothera Research Station
↓
4King Edward Point, South Georgia

Each leg is a separate booking and a separate chance to be weathered out. Build spare days into the chain, not onto the end of it.

Where it is

Halley VI Research Station, Brunt Ice Shelf, Antarctica · 75.5682°S 25.5085°W · Open in Google Maps · OpenStreetMap

Key locations

Halley VI Research Station — coordinates as published by BAS; the shelf beneath it flows west at up to 2 km a year
75.5682°S 25.5085°W
Rothera Research Station — BAS station since October 1975, running meteorology and ozone monitoring
67.5689°S 68.1248°W
Akademik Vernadsky (formerly Faraday) — 65°15'S 64°16'W per the Ukrainian operator; the second station in the 1985 paper
65.2500°S 64.2667°W
King Edward Point, South Georgia — BAS ran a Dobson series here from 1971 to 1982
54.2833°S 36.5000°W
South Pole Observatory — established for the IGY in 1957 at 2,837 m; longitude is undefined at the pole
90.0000°S 0.0000°E
Mauna Loa Observatory — home of World Standard Dobson D083, the reference for the entire network
19.5362°N 155.5763°W

Coordinates are for orientation and are accurate to roughly the width of the feature named, not to a doorway. Several of these points are inside protected areas or need a permit, a guide or a boat — read the access notes above before you plan a route to any of them.

Sources & further reading — checked 25 August 2026

Atmospheric Chemistry and Physics — Zhang, Solomon, Stone, Shanklin, Eveson, Colwell, Burrows, Weber, Levelt, Kramarova and Haffner, 'On the use of satellite observations to fill gaps in the Halley station total ozone record', ACP 21, 9829–9838 (2021). The February 2017 closure of Halley for Brunt Ice Shelf stability; the loss of the 2017 and 2018 austral springs; eleven satellite instruments including GOME-2, SBUV, OMI and OMPS; the day-of-year delta method reproducing monthly ground values to 1.1 ± 6.2 DU against 4.6 DU for raw satellite data; and post-2000 September recovery of 1.34 ± 0.64 DU per year
Atmospheric Chemistry and Physics — full text of Zhang et al. (2021). The explicit statement that no routine ozone data are available at Halley in May, June and July when the sun is below the horizon; that only daily averages exist for 1956–1971 and individual measurements from 1972; the exclusion of the provisional 2019 automated Dobson for showing substantially larger negative deltas, and the treatment of 2020 as likely inconsistent
Nature — J. D. Shanklin, 'Reflections on the ozone hole', Nature 465, 34 (2010), NASA-hosted PDF. Shanklin's own account: ground measurements timed to satellite overpasses and sent to the Satellite Ozone Analysis Center at Livermore; his letter to its head asking whether the satellites confirmed low values; 'I never received a reply — perhaps another lucky break for our team'; and averaging around a latitude circle that 'would have effectively hidden the ozone hole, because of its offset from the pole'
Nature — Farman, Gardiner and Shanklin, 'Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction', Nature 315, 207–210 (16 May 1985). The original letter's abstract and metadata: spring total ozone in Antarctica having fallen considerably, the proposed sensitivity of the cold Antarctic stratosphere to chlorine growth, and the three authors' affiliation to the British Antarctic Survey, NERC, Cambridge
Nature — Stolarski, Krueger, Schoeberl, McPeters, Newman and Alpert, 'Nimbus 7 satellite measurements of the springtime Antarctic ozone decrease', Nature 322, 808–811 (28 August 1986). The Goddard team's satellite confirmation using SBUV and TOMS from November 1978 onward: a 40% decrease in the ozone minimum and 20% in the surrounding maximum across 1979–1985, with the minimum reached in mid-October and the phenomenon shown to be regional rather than global
Nature — Susan Solomon, 'The discovery of the Antarctic ozone hole', News and Views, 23 October 2019. Erik Conway of NASA's Jet Propulsion Laboratory on the Goddard quality-control software set to 'mark as potentially bad data anything that showed levels below a certain amount', and that 'when the Goddard folks mapped all these flags of potentially bad data, they were all over the Antarctic, exactly where the British Antarctic Survey said it should be'
British Antarctic Survey — Dobson Spectrophotometer, Halley facility page. BAS describing this as the instrument that led to the discovery of ozone depletion over Antarctica; the station coordinates of 75.56821°S, 25.50852°W; and the note that ozone values began dropping around 1970 and continued to about 1999
British Antarctic Survey — Halley VI Research Station facility page. Occupation from 15 January 1956, summer staffing of up to 52, the instrument suite from spectrophotometers to magnetometers and the Clean Air Sector Laboratory, and the 2017 move of 23 km inland to avoid the path of large cracks in the ice
British Antarctic Survey — 'Automated Halley monitors the ozone hole over Antarctica' (16 September 2020). The auto-Dobson housed in a white container with a micro-turbine in a green one and services in a red one; project manager Thomas 'Barney' Barningham on a second year of capturing the springtime development of the hole; and Jonathan Shanklin on the automated Dobson allowing finer study of the ozone layer
British Antarctic Survey — 'Halley VI Research Station – relocation success'. The 23 km relocation upstream, a 13-week operation completed on 2 February 2017 using lifting frames and plastic slip sheets on the eight modules, and the decision not to winter a team as a safety precaution
British Antarctic Survey — 'Brunt Ice Shelf in Antarctica calves' (26 February 2021). The 1,270 km² calving of 26 February 2021 following the North Rift detected in November 2020 and advancing up to 1 km a day; the station described as moved 32 km inland in 2016-17, a figure that differs from BAS's own 23 km elsewhere; and unoccupied winters since 2017 because evacuation would be difficult below minus 50
British Antarctic Survey — Brunt Ice Shelf movement project. Chasm 1 resuming movement in 2012 after roughly 35 dormant years; the Halloween Crack appearing in October 2016 about 17 km north of the station and across resupply routes; ApRES measuring chasm width every two hours and 15 GPS instruments recording deformation daily; the January 2023 calving; and the shelf moving about 4 m a day afterwards against 1–2.5 m before
British Antarctic Survey Polar Data Centre — metadata record GB/NERC/BAS/PDC/00255, 'British Antarctic Survey Ozone Data'. Temporal coverage beginning 17 September 1956 and ongoing; Dobson spectrophotometers at Halley and Faraday/Vernadsky, SAOZ and a Bentham spectro-radiometer at Rothera; King Edward Point 1971–1982; and the credit line to J. D. Shanklin, British Antarctic Survey, Cambridge
British Antarctic Survey (legacy met pages) — BAS Ozone index, maintained by J. D. Shanklin. The Halley Dobson observing season running from the end of August to mid-April; the four observation types of direct sun, zenith blue, zenith cloud and moon; Dobson 31 in manual use and Dobson 73 in automated mode at Halley; a slow increase of about 1 DU a year in the October minimum since 1994; and the statement that marked differences between satellites demonstrate the need for verification by ground-based stations
British Antarctic Survey (legacy met pages) — ozone data metadata description. Dobson 103 at Halley from February 1991 to December 2005, Dobson 73 from December 2005 to February 2012 and Dobson 31 from February 2012, with overlaps for calibration transfer; a temporary automated Dobson 73 in January–February 2018; observation codes including ADDS, CDDS, CDFM and ADZ; the 0.9743 WMO factor applied to 1957–1972 Powell-coefficient data; and lunar observations outside the seasonal blocks that are not in the standard files
British Antarctic Survey (legacy met pages) — BAS Dobson Manual (PDF). The operating manual the observers use: wavelength pairs A, C and D; the optical wedge nulled against a rotating sector wheel and photomultiplier; direct sun to mu 2.8, zenith blue to 2.6 and as far as 10.0 at season ends, focused moon 7 days either side of full at mu 1.2–3.5, and nickel-sulphate filtered sun at mu 3.0–6.5; monthly standard-lamp tests agreeing within 0.5; and the 20-microamp limit on the photomultiplier tube
British Antarctic Survey (legacy met pages) — history of Antarctic ozone measurement. Dobson's own recollection that the September and October 1956 values at Halley Bay 'were about 150 units lower than was expected' and were first suspected to be instrument error until the pattern repeated the following year; and mean October ozone falling around 3% a year since 1976 while chlorine rose about 3% a year
NASA Ozone Watch — What is the ozone hole?. The 220 Dobson Unit definition of the hole and the justification for it: total column values below 220 DU were not observed prior to 1979, so the threshold marks catalysed loss from chlorine and bromine compounds rather than natural variation
NASA Ozone Watch — What is a Dobson Unit?. One Dobson Unit as a layer of pure ozone 0.01 mm thick at 0°C and 1 atmosphere, about 2.69 × 10^16 molecules per square centimetre; a normal column of roughly 300 DU or three millimetres; and hole values around 100 DU
NASA Ozone Watch — Annual Antarctic ozone hole statistics. The satellite-era table: minimum 194 DU and 1.1 million km² in 1979; 124 DU and 18.8 million km² in 1985; 84 DU in 2006; and 127 DU on 25 September 2025 with a maximum area of 22.9 million km² on 9 September — the series that cannot reach back before 1979
NASA — Nimbus-7 TOMS Data Products User's Guide (PDF). Nimbus-7 launched 24 October 1978 with archived data from 31 October 1978 to 6 May 1993; six wavelengths at 312.34, 317.35, 331.06, 339.66, 359.88 and 379.95 nm; scanning in 3-degree steps to 51 degrees each side of nadir; radiative transfer tables to 88 degrees solar zenith angle; and the Level-3 rule that only data with quality flag 0 are used to compute the averages
NASA Technical Reports Server — Bhartia, Krueger, Taylor and Wellemeyer, 'Estimation of Errors in the TOMS Total Ozone Measurement During the Antarctica Ozone Campaign of August/September 1987' (1989). The Goddard team's own error analysis: that low stratospheric temperatures, polar stratospheric clouds and extremely low ozone amounts 'were not anticipated in the design' of the retrieval algorithm; calibration drift of about 6 m-atm-cm by October 1987; and possible underestimation by up to 10 m-atm-cm very close to the terminator
NOAA Global Monitoring Laboratory — Dobson handbook, Section 2 (NOAA Technical Report NESDIS 74 series). The AD double-pair method and the 1.388 absorption coefficient adopted as standard; the worked total-ozone example giving 341 DU; the Vigroux-to-Bass-Paur change on 1 January 1992 reducing reported ozone by 2.6%; Dobson 83's long-term precision better than ±1% since 1962; and standard-lamp uncertainties of 2.2%, 1.1% and 0.7% at mu of 1, 2 and 3 for a 300 DU column
NOAA Global Monitoring Laboratory — Dobson calibration news. World Standard Dobson D083 held at Mauna Loa; regional standards intercompared against it about every two years and propagating the calibration to station instruments; monthly standard-lamp checks between comparisons; and NOAA hosting the WMO/GAW World Dobson Calibration Center whose work also underpins verification of NOAA and NASA satellite ozone records
NOAA Global Monitoring Laboratory — Mauna Loa Observatory. The observatory's stated position at 19.5362°N, 155.5763°W and 3,397 metres above sea level, and continuous atmospheric monitoring since the 1950s — the physical location of the instrument every other Dobson in the world is measured against
NOAA Global Monitoring Laboratory — South Pole Observatory. The observatory established at the geographical South Pole in 1957 as part of the International Geophysical Year, at an elevation of 2,837 metres — the other long Antarctic ozone site and the reason Halley is not the only baseline in the region
Japan Meteorological Agency — Dobson Spectrophotometer Measurement Principle and Automation System. An independent national met service's specification of the same optics, giving pair A as 305.5 and 325.0 nm, C as 311.5 and 332.4 nm and D as 317.5 and 339.9 nm — figures that do not match the BAS manual's — plus the description of slits S2 and S3, the rotating sector wheel and the optical wedge reducing the longer wavelength to the shorter one's intensity
UNEP Ozone Secretariat — Scientific Assessment of Ozone Depletion 2022, Executive Summary (PDF). The projection that total column ozone returns to 1980 values 'around 2066 in the Antarctic, around 2045 in the Arctic, and around 2040 for the near-global average (60°N–60°S)'; continued Antarctic recovery since 2000; and the warning that retiring space-borne instruments without replacement will impede future monitoring
UNEP Ozone Secretariat — the Montreal Protocol. The Protocol signed in 1987 and entered into force in 1989, amended six times, most recently by the 2016 Kigali Amendment covering the phase-down of hydrofluorocarbons
World Ozone and Ultraviolet Radiation Data Centre — About. WOUDC as one of six World Data Centres of the WMO Global Atmosphere Watch, operated by the Meteorological Service of Canada; founded in 1960 as the World Ozone Data Centre and renamed in 1992; holding over 500 registered stations from more than 150 contributing organisations, with total column ozone, UV, ozonesonde, lidar and Umkehr profile data — including the Halley series
RISKS Digest, Volume 3, Issue 29 (1 August 1986) — contribution by Bill McGarry. The earliest dated instance of the legend we could find, fifteen months after the Farman paper and four weeks before the Goddard confirmation appeared in Nature: 'And why did the satellite fail to report this hole? Because it had been programmed to reject values that fell outside the ‘normal’ range!'
University of Melbourne, Statistical Consulting Centre — guidance on outliers. The legend in current university statistics teaching: 'Antarctic satellite collection data systems automatically deleted outliers, and as a result the hole in the ozone layer was detected much later than it could have been' — offered to students as a reason not to remove outliers
University of Arizona — NATS 101 lecture notes, 'Ozone Part III' (PDF). The same claim taught in an undergraduate atmospheric-science course: 'TOMS detected the developing hole, but the anomalously low readings were rejected as ‘noise’ by the computer program set up to process the data !!'
Antarctic Treaty Secretariat — Protocol on Environmental Protection to the Antarctic Treaty. The Madrid Protocol signed 4 October 1991 and in force from 1998, designating Antarctica 'a natural reserve, devoted to peace and science', with Annexes I–IV in force from 1998, Annex V from 2002 and Annex VI awaiting entry into force
GOV.UK — Visits to Antarctica: how to apply for a permit. That anyone on a British expedition to Antarctica, or taking a British vessel or aircraft there, needs a permit from the FCDO Polar Regions Department; at least four months' notice for a new or unusual application and two months for a repeat; and that late applications may not be considered
GOV.UK — Antarctica / British Antarctic Territory travel advice, entry requirements. The FCDO's blunt statement that travelling to any part of Antarctica without permission can mean a fine or a prison sentence, and that tour operators normally obtain permits on behalf of organised visits
British Antarctic Survey — Rothera Research Station facility page. Rothera at 67.568889°S, 68.1248°W, operating since 25 October 1975, and listed as running meteorology and ozone monitoring — the BAS site that continued measuring while Halley was dark
British Antarctic Survey — King Edward Point Research Station facility page. King Edward Point, South Georgia, at 54.283333°S, 36.5°W, occupied since 1909 and run by BAS 1969–82 and again from 2001 — the site of the BAS Dobson series that ran 1971 to 1982
National Antarctic Scientific Center of Ukraine — Akademik Vernadsky Station. Vernadsky at 65°15'S, 64°16'W, the former British Faraday station transferred in 1996, with an ozonometric laboratory among its facilities — the second station in the 1985 paper, still measuring under a different flag
US Geological Survey EROS — Earthshots: Halley Station. Halley VI as eight interlinked pods on skis since 2012, moved to the eastern side of Chasm 1 in the 2016-17 summer, on a floating ice shelf flowing west at up to 2 km a year, tracked in Sentinel-2 imagery from November 2016 to February 2022

Official and scientific bodies are the authority for safety, regulatory and scientific claims. Commercial operators are used only for practical detail such as tour length, meeting points and indicative pricing — never for a safety or scientific statement.

How this was made

Desk research. Compiled from official bodies, scientific and conservation sources, established journalism and licensed operators. Not based on a personal visit.

Editor’s method note — what we checked, corrected and could not verify

Desk research only. Nobody from this publication has been to Antarctica or seen the instrument, and there is no lawful route by which a visitor could.
Every URL cited was opened and read before citation. Sources we could not read are listed at the end of this note and are not cited anywhere in the piece.
The debunk rests on two separate strands and we keep them separate. The first is documentary: NASA's own Nimbus-7 TOMS User's Guide describes a quality-flag architecture in which flagged retrievals are excluded from Level-3 gridded averages, not deleted, and Erik Conway of NASA JPL states in Nature that the Goddard flags, when mapped, drew the hole exactly where BAS said it was. The second is Jonathan Shanklin's 2010 recollection about the Satellite Ozone Analysis Center and latitude-circle averaging. Shanklin was one of the three authors, he is describing someone else's method twenty-five years later, and he hedges it himself with the word 'probably'. We present it explicitly as his account and place the article's weight on the documented 2017-18 gap, which nobody disputes.
We could not open the two peer-reviewed history-of-science papers on the ozone hole's visual and documentary record that would have let us trace the legend's transmission properly. The earliest dated instance we can actually cite is the RISKS Digest of 1 August 1986. We do not claim it is the origin, only that it is the earliest we opened.
Wavelength figures for the Dobson's A, C and D pairs differ between the BAS Dobson Manual and the Japan Meteorological Agency's specification of the same instrument. We print both and name both, and we have not averaged them or picked one.
The distance Halley VI was moved in the 2016-17 season is given by BAS as 23 km on its relocation announcement and its Brunt Ice Shelf monitoring page, and as 32 km on its February 2021 calving release. Both figures are BAS's own. We print both.
Figures describing the ozone hole's area and minimum values come from NASA Ozone Watch and are satellite measurements. We say so in the body rather than presenting them as ground truth, because the argument of this dossier is precisely that instrument and measurement are not separable.
The 1.1 ± 6.2 DU accuracy figure for the reconstructed 2017-18 seasons is the authors' own validation statistic against withheld Dobson data, not an independent check. Their exclusion of the 2019 automated Dobson data, and their treatment of 2020 as likely inconsistent, is reported as they state it.
Coordinates in the panel come from the operators themselves — BAS facility pages for Halley, Rothera and King Edward Point, the National Antarctic Scientific Center of Ukraine for Vernadsky, and NOAA for Mauna Loa. The SCAR Composite Gazetteer of Antarctica, which would have been the preferred authority, was unreachable: its old AADC addresses redirect to a site that returns nothing without JavaScript. The South Pole point is given as 90°S with a nominal longitude, because longitude is undefined there. We noticed that the BAS facility page for Signy appears to list its latitude and longitude the wrong way round, so we did not use it.
Sources we could not read, and therefore did not cite: two open-access history-of-science papers by Sebastian Grevsmuhl on HAL, both blocked at 403 by the host's bot protection; the Comptes Rendus Geoscience paper 'The discovery of the Antarctic Ozone Hole' on ScienceDirect, robots-blocked; a Smithsonian repository PDF of a Susan Solomon account, 403; the joint NOAA/NASA news release on the 2025 ozone hole, 403; the SCAR Composite Gazetteer and the SCAR GSSG station coordinate list, redirect-blocked and robots-blocked respectively; the COMNAP Antarctic Facilities database, which returned no content; the Beck Optronic manufacturer case study on the Dobson, which returned no content; the BAS monthly-mean data file ZOZ5699.DAT, which our tools received as binary; and a GOV.UK permit page that returned 404 and has been replaced by the guidance we do cite.
Things we could not verify: which Dobson instrument was physically at Halley in 1985, the BAS metadata we opened listing the instrument sequence only from February 1991; whether the instrument is made of brass, as the popular retelling has it, no manufacturer or operator source we could open describing its construction; the correct wavelength values for the A, C and D pairs, two authoritative sources disagreeing; how many days a year the sun is fully below the horizon at Halley, for which we found no primary figure and so state only the three named blind months; whether Halley VI was moved 23 or 32 kilometres; the October mean total ozone values at Halley for any specific year, the BAS data files being unreadable to us and the 1985 paper sitting behind a paywall; who at the Satellite Ozone Analysis Center received Shanklin's letter, or whether it arrived; how many lunar observations exist at Halley outside the seasonal data blocks; and whether Halley will be staffed through a winter again.

AI is used to draft this text, and a human checks it. Every figure, date and quotation above was verified by Tony Hall against the source cited for it in the reference list; where sources disagree, the disagreement is shown rather than resolved, and where a claim could not be confirmed it is either marked unverified or left out. The illustrations are AI-created and labelled as such — no photograph on this site is presented as a record of a real place. Full disclosure · Editorial policy.

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Blind Until August: The Halley Dobson and the Two Seasons Its Record Lost