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Unprecedented Arctic ozone loss in 2011



Chemical ozone destruction occurs over both polar regions in local winter-spring. In the Antarctic, essentially complete removal of lower-stratospheric ozone currently results in an ozone hole every year, whereas in the Arctic, ozone loss is highly variable and has until now been much more limited. Here we demonstrate that chemical ozone destruction over the Arctic in early 2011 was--for the first time in the observational record--comparable to that in the Antarctic ozone hole. Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 per cent over 18-20 kilometres altitude. Our results show that Arctic ozone holes are possible even with temperatures much milder than those in the Antarctic. We cannot at present predict when such severe Arctic ozone depletion may be matched or exceeded.
Unprecedented Arctic ozone loss in 2011
Gloria L. Manney
, Michelle L. Santee
, Markus Rex
, Nathaniel J. Livesey
, Michael C. Pitts
, Pepijn Veefkind
, Eric R. Nash
Ingo Wohltmann
, Ralph Lehmann
, Lucien Froidevaux
, Lamont R. Poole
, Mark R. Schoeberl
, David P. Haffner
Jonathan Davies
, Valery Dorokhov
, Hartwig Gernandt
, Bryan Johnson
, Rigel Kivi
, Esko Kyro
, Niels Larsen
Pieternel F. Levelt
, Alexander Makshtas
, C. Thomas McElroy
, Hideaki Nakajima
, Maria Concepcio
n Parrondo
David W. Tarasick
, Peter von der Gathen
, Kaley A. Walker
& Nikita S. Zinoviev
Chemical ozone destruction occurs over both polar regions in local winter–spring. In the Antarctic, essentially complete
removal of lower-stratospheric ozone currently results in an ozone hole every year, whereas in the Arctic, ozone loss is
highly variable and has until now been much more limited. Here we demonstrate that chemical ozone destruction over
the Arctic in early 2011 was—for the first time in the observational record—comparable to that in the Antarctic ozone
hole. Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in
ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 per cent over 18–20
kilometres altitude. Our results show that Arctic ozone holes are possible even with temperatures much milder than
those in the Antarctic. We cannot at present predict when such severe Arctic ozone depletion may be matched or
Since the emergence of the Antarctic ‘ozone hole’ in the 1980s
elucidation of the chemical mechanisms
and meteorological con-
involved in its formation, the likelihood of extreme ozone
depletion over the Arctic has been debated. Similar processes are at
work in the polar lower stratosphere in both hemispheres, but differ-
ences in the evolution of the winter polar vortex and associated polar
temperatures have in the past led to vastly disparate degrees of spring-
time ozone destruction in the Arctic and Antarctic. We show that
chemical ozone loss in spring 2011 far exceeded any previously
observed over the Arctic. For the first time, sufficient loss occurred
to reasonably be described as an Arctic ozone hole.
Arctic polar processing in 2010–11
In the winter polar lower stratosphere, low temperatures induce
condensation of water vapour and nitric acid (HNO
) into polar
stratospheric clouds (PSCs). PSCs and other cold aerosols provide
surfaces for heterogeneous conversion of chlorine from longer-lived
reservoir species, such as chlorine nitrate (ClONO
) and hydrogen
chloride (HCl), into reactive (ozone-destroying) forms, with chlorine
monoxide (ClO) predominant in daylight
In the Antarctic, enhanced ClO is usually present for 4–5 months
(through to the end of September)
, leading to destruction of most
of the ozone in the polar vortex between ,14 and 20 km altitude
Although ClO enhancement comparable to that in the Antarctic
occurs at some times and altitudes in most Arctic winters
, it rarely
persists for more than 2–3 months, even in the coldest years
. Thus
chemical ozone loss in the Arctic has until now been limited, with
largest previous losses observed in 2005, 2000 and 1996
The 2010–11 Arctic winter–spring was characterized by an
anomalously strong stratospheric polar vortex and an atypically long
continuously cold period. In February–March 2011, the barrier to
transport at the Arctic vortex edge was the strongest in either hemi-
sphere in the last ,30 years (Fig. 1a, Supplementary Discussion).
The persistence of a strong, cold vortex from December through to
the end of March was unprecedented. In the previous years with most
ozone loss, temperatures (T) rose above the threshold associated with
chlorine activation (T
, near 196 K, roughly the threshold for the
potential existence of PSCs) by early March (Fig. 1b, Supplementary
Figs 1, 2). Only in 2011 and 1997 have Arctic temperatures below T
persisted through to the end of March, sporadically approaching a
vortex volume fraction similar in size to that in some Antarctic winters
(Fig. 1b). In 1996–97, however, the cold volume remained very limited
until mid-January and was smaller than that in 2011 at most times
during late January through to the end of March (Fig. 1b, Supplemen-
tary Figs 1, 2).
Daily minimum temperatures in the 2010–11 Arctic winter were
not unusually low, but the persistently cold region was remarkably
deep (Supplementary Figs 1, 2). Temperatures were below T
more than 100 days over an altitude range of ,15–23 km, compared
to a similarly prolonged cold period over only ,20–23 km altitude in
1997; below ,19 km altitude, T , T
continued for ,30 days longer
in 2011 than in 1997 (Supplementary Fig. 1b). In 2005, the previous
year with largest Arctic ozone loss
, T , T
occurred for more than
100 days over ,17–23 km altitude, but all before early March.
The winter mean volume of air in which PSCs may form (that is,
with T , T
), V
, is closely correlated with the potential for ozone
. In 2011, V
(as a fraction of the vortex volume) was the
largest on record (Fig. 1c). Both large V
and cold lingering well into
spring are important in producing severe chemical loss
, and
2010–11 was the only Arctic winter during which both conditions
have been met. Much lower fractional V
in 1997 than in 1996, 2000,
2005 or 2011 (Fig. 1c) is consistent with less ozone loss that year
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA.
Alfred Wegener
Institute for Polar and Marine Research, D-14473 Potsdam, Germany.
NASA Langley Research Center, Hampton, Virginia 23681, USA.
Royal Netherlands Meteorological Institute, 3730 AE De Bilt, The
Delft University of Technology, 2600 GA Delft, The Netherlands.
Science Systems and Applications, Inc., Lanham, Maryland 20706, USA.
Science Systems and Applications, Inc., Hampton,
Virginia 23666, USA.
Science and Technology Corporation, Lanham, Maryland 20706, USA.
Environment Canada, Toronto, Ontario, Canada M3H 5T4.
Central Aerological Observatory, Dolgoprudny
141700, Russia.
NOAA Earth System Research Laboratory, Boulder, Colorado 80305, USA.
Arctic Research Center, Finnish Meteorological Institute, 99600 Sodankyla
, Finland.
Danish Climate
Center, Danish Meteorological Institute, DK-2100 Copenhagen, Denmark.
Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
Arctic and Antarctic Research Institute, St
Petersburg 199397, Russia.
National Institute for Environmental Studies, Tsukuba-city, 305-8506, Japan.
National Institute for Aerospace Technology, 28850 Torrejo
n De Ardoz, Spain.
University of
Toronto, Toronto, Ontario, Canada M5S 1A7.
00 MONTH 2011 | VOL 000 | NATURE | 1
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Factors playing secondary parts in governing interannual variability
in ozone destruction, including vortex strength, structure and posi-
tion relative to the cold region, also favour large loss in 2011 (Sup-
plementary Figs 2, 3, Supplementary Discussion). However, despite
the fraction of the vortex with T , T
and mid-March temperatures
sporadically approaching those seen in the Antarctic (Fig. 1b,
Supplementary Fig. 1a), even in 2011 temperatures were much higher,
and the cold regions much smaller, than those in most Antarctic
Satellite trace-gas and PSC measurements highlight the stark con-
trast between polar processing in 2010–11 and that in typical Arctic
winters, and the parallels with Antarctic conditions (Figs 2, 3). In 2011,
PSCs or aerosols were abundant until mid-March (Fig. 3a; consistent
with a deep region with T , T
, Fig. 3b), much later than usual in the
, with vortex-average amounts at some altitudes similar to
those in the Antarctic and dramatically larger than the near-zerovalues
at that time in most Arctic winters. Furthermore, PSCs in 2011
spanned an altitude range comparable to that in the Antarctic, an
uncommon occurrence in the Arctic
. Particles in long-lasting
PSCs can grow large enough to sediment, resulting in denitrification,
permanent removal of HNO
from the stratosphere
. By late March
2011 no PSCs remained (Fig. 3a), yet HNO
mixing ratios were much
lower than observed in any previous Arctic winter (Fig. 2a). The con-
tinuing depression in HNO
after PSCs had evaporated indicates
denitrification. Albeit less severe than in typical Antarctic winters
(Fig. 2b, c, 3c), the extent and degree of denitrification in 2011 were
unmatched in the Arctic, approaching the range of Antarctic condi-
tions for the first time.
Decreasing HCl and increasing ClO signify chlorine activation
(Fig. 2d–i). Some ClO enhancement has occurred in all recent
Arctic winters, but has never been as prolonged and extensive as that
in 2011. In late February, high ClO pervaded the sunlit portion of the
vortex. The 2011 values vastly exceed the range previously observed in
the Arctic from late February through to the end of March. They also
briefly lie outside the Antarctic seasonal envelope, primarily because
the higher solar zenith angles of the Antarctic measurements used
here lead to ,30% lower ClO under fully activated conditions. In late
February, HCl values (unaffected by solar zenith angle issues) fall
along the lower boundary of the Antarctic envelope, confirming the
picture seen in ClO. The vertical extent of chlorine activation was also
comparable to that in the Antarctic (Fig. 3d, e).
In previous cold Arctic winters, chlorine was deactivated (converted
from ozone-destroying forms into less reactive reservoir species) by
; even in 1997, ClO started to decline by late February
(Fig. 2g). In 2011, by contrast, ClO began decreasing rapidly only about
a week earlier than is typical in the Antarctic. ClO data in late February
1997 indicate that not only were maximum values lower than those in
early March 2011, but also the vertical range of enhancement was
shallower, with weaker activation at low altitudes than in 2011
(Fig. 3e), consistent with the higher altitudes and decreasing extent
(Figs 1b, 3b, Supplementary Fig. 2) of T , T
When chlorine is deactivated, whether it is converted first into HCl
or ClONO
depends sensitively upon HNO
and ozone abundances. In
the Arctic, chlorine is normally deactivated through initial reformation
of ClONO
. In the severely denitrified and ozone-depleted Antarctic
vortex, production of ClONO
is suppressed and that of HCl highly
. In March 2011, the recovery of HCl followed a much
more Antarctic-like pathway than has been observed in any other
Arctic winter.
The largest Arctic chemical ozone loss was previously observed in
2005, followed closely by 2000 and 1996
. Although low tempera-
tures persisted until the end of March 1997, the ozone loss in that year
was far less. No previous year rivals 2011, when the evolution of Arctic
ozone more closely followed that typicalof the Antarctic (Fig. 2j). Ozone
profiles in late March 2011 resemble typical Antarctic late-winter pro-
files much more strongly than they do the average Arctic one (Fig. 3f).
Because mixing in April 2011 (for example, lamination events larger
than that shown in Fig. 3f) entrained ozone-rich air into the vortex, the
slight decrease in vortex-averaged ozone at a potential temperature of
485 K from 26 March to 20 April (from ,1.8 to ,1.6 p.p.m.v., Fig. 2j)
indicates continuing chemical loss during this interval.
Estimates of chemical ozone loss
Chemical loss is difficult to quantify in the Arctic, where transport
from above replenishes ozone in the lower stratospheric vortex,
obscuring the signature of chlorine-catalysed destruction
. The
evolution of the long-lived trace gas nitrous oxide (N
O) reflects steady
downward transport throughout the 2010–11 winter–spring, indi-
cating that subsidence partially masked chemical loss. Horizontal
transport can also confound the signature of chemical loss, bringing
air into the vortex that has either higher
or lower
concentrations of
ozone, depending on the altitude and latitude from which it originates.
Representative results from two types of chemical loss calcula-
based on balloon-borne and satellite observations are shown
in Fig. 4. The differences (up to ,0.4 p.p.m.v. at the end of March
2011) in estimates derived from the various methods and data sets
imply some uncertainty in the chemical loss determination. Year-to-
year differences in the amount of ozone loss are very similar when
obtained from any method/data set combination, however, indicating
a high degree of precision in the relative amount of calculated loss
Max. PV gradient (10
(s deg)
1 Jun. 1 Jul. 1 Aug. 1 Sep. 1 Oct.
a PV gradient, 1979–2011
1 Dec. 1 Jan. 1 Feb. 1 Mar. 1 Apr.
1980 1985 1990 1995 2000 2005 2010
b Vortex fraction of low temperature air, 1979–2011
c Winter mean vortex fraction of low temperature air
Figure 1
Meteorology of the Arctic lower stratosphere. a, Vortex strength
(as indicated by maximum potential vorticity
(PV) gradients) at 460 K
potential temperature (,18 km altitude, ,65 hPa level). b, Fraction of vortex
volume at potential temperatures between 390 and 550 K with a temperature
less than the chlorine activation threshold (T
). Light (dark) grey shading
shows range of Arctic (Antarctic) values for 1979–2010. Antarctic dates are
shifted by six months (top axis in a) to show the equivalent season. c,Winter
mean V
during the past 32 years, expressed as a fraction of vortex volume.
Red, orange, green, purple and blue lines/bars show the 2010–11, 2004–05,
1999–2000, 1996–97 and 1995–96 Arctic winters, respectively.
2 | NATURE | VOL 000 | 00 MONTH 2011
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between different years. Chemical destruction was severe between
,16 and 22 km altitude, with the largest loss exceeding 2.5 p.p.m.v.
by 26 March 2011 (Fig. 4a). By 31 March 2011, chemical loss was
nearly double that in 2005 from ,18 to above 22 km, and similar to
that in 2005 at lower altitudes (Fig. 4b, c). From ,18 to 20 km, more
than 80% of the ozone present in January had been chemically
destroyed by late March. Chemical removal in 1996 and 2000 started
at a rate similar to that in 2011 (Fig. 4c), but ceased by late March;
maximum losses in 2000 approached those in 2011, but extended over
a much smaller vertical range (Fig. 4b). Loss in 1996, 2000 and 2005
considerably exceeded that in 1997, with greater destruction at lower
altitudes in those years contributing more to total column loss
Chemical loss in 2011 was two to three times larger than that in 1997,
and about twice that in 1996 and 2005 above ,16 km; from ,15 to
23 km it was comparable to that in the Antarctic ozone hole in 1985
Single ozone-sonde station measurements in early April 2011 suggest
continuing ozone loss (Fig. 4c).
Although the meteorology during March–April was similar in 1997
and 2011, ozone loss was much more pronounced in 2011. Photo-
chemical box model simulations (Supplementary Fig. 4, Supplemen-
tary Discussion) elucidate how early winter conditions set the stage for
record springtime ozone destruction in 2011. Chlorine activation
brought on by enduring cold from December through to the end of
February led to ,0.7–0.8 p.p.m.v. lower ozone at the beginning of
March 2011 (Figs 2j, 4c). The early onset of continuous cold also
facilitated formation of PSC particles large enough to sediment, result-
ing in ,4 p.p.b.v. less HNO
by March in 2011 than in 1997 (Fig. 2a).
The degree of denitrification has a profound impact on the severity of
springtime Arctic ozone loss
. By delaying chlorine deactivation,
lower HNO
by 1 March was responsible for ,0.6 p.p.m.v. more ozone
Vortex average HNO
1 Jun. 1 Jul. 1 Aug. 1 Sep. 1 Oct.
d HCl
g ClO
j O
26 Mar.
Vortex average HCl (p.p.b.v.)
28 Feb.
29 Aug.
28 Feb. 29 Aug.
Vortex average ClO (p.p.b.v.)
Vortex average O
(p.p.b.v.) HCl (p.p.b.v.) ClO (p.p.b.v.) O
1 Dec. 1 Jan. 1 Feb. 1 Mar. 1 Apr.
26 Sep.
26 Mar. 26 Sep.
Figure 2
Chemical composition in the lowerstratosphere. al, Maps (right)
and vortex-averaged time series (left) at 485 K potential temperature (,20 km,
,50 hPa) for four different gases: HNO
(a, b, c), HCl (d, e, f), ClO (g, h, i) and
(ozone; j, k, l); mixing ratios from Aura MLS are shown. Averaging for the
time series is done within the white contour shown on the maps. Blue (purple)
triangles on time series, 1995–96 (1996–97) values from UARS MLS. Line
colours/shading as in Fig. 1, but shading is for Aura MLS measurements from
2005–10. Antarctic dates are shifted by six months (top axis on time series) to
show the equivalent season. Vertical lines show dates of maps in 2011 (2010) in
the Arctic (Antarctic). Black overlays on HNO
maps, T
(,196 K at this
level); HNO
may be sequestered in PSCs at lower temperatures. Dotted black/
white contour on ClO maps, 92u SZA, poleward of which measurements were
taken in darkness. Yellow/black triangles on ozone maps, locations of the
profiles in Fig. 3.
00 MONTH 2011 | VOL 000 | NATURE | 3
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loss after that date in 2011 than in 1997 (Supplementary Fig. 4,
Supplementary Discussion). The effects of denitrification and early-
winter loss together account for the disparity in ozone depletion in
these two winters (,1.5 p.p.m.v. more loss at 460 K in 2011 than in
1997, Fig. 4c, Supplementary Fig. 4). Loss as severe as that in 2011 thus
requires T , T
, with consequent chlorine activation and ozone
destruction, early in winter (as in 1996, 2000 and 2005, but not in
1997), a cold period and region before March sufficient to allow wide-
spread denitrification, and the persistence of a cold polar vortex into
April (as in 1997, but not in 1996, 2000 or 2005).
0 2 4 6
Altitude (km)
190 210
Temperature (K)
0 2 4 6 8
0.0 1.0 2.0
HCl (p.p.b.v.)
0.0 0.8 1.6
ClO (p.p.b.v.)
0 2 4 6
Pressure (hPa)
Figure 3
Vertical composition information. a, Red, PSCs/aerosol amounts
averaged in the vortex over a week centred around 25 February 2011; dark blue,
the average for the same week in 2007–10; grey, the average over the equivalent
period (centred on 28 August) for the Antarctic in 2006–10; lavender, the Arctic
average for a week centred around 26 March 2011. (In late winter–spring,
maximum PSC altitudes are generally higher in the Arctic because early winter
PSC activity redistributes HNO
and water vapour to lower altitudes in the
). bf, Daily average profiles of MERRA temperatures (b) and MLS
(c), HCl (d), ClO (e) and ozone (f). Red lines, data from a 4u 3 15u
latitude3 longitude box around 79u N, 12u E; in c, f, taken on 26 March; in
b, d, e, on 6 March 2011. Lavender, 7-day average for 2005–10 (1980–2010 for
b) centred on the same location and days. Grey, profiles in a similar box in the
Antarctic (79u S, 12u E) on 26 September for c, f, and on 8 September 2010 for
b, d, e. Dotted black line in b, approximate T
(195 K), see text. Purple line in
b, 7-day average around 6 March 1997, centred on same location. Purple line in
e, a midday ClO profile from UARS MLS on 26 February 1997 averaged in an
8u 3 30u box centred at the same Arctic location. A high-resolution ozone-
sonde profile at Ny A
lesund on 26 March 2011 (black in f) agrees well with
MLS; lamination, a signature of mixing with ozone-rich extra-vortex air, is
apparent as a local maximum near 60 hPa.
Potential temperature (K)
1 Jan. 1 Feb. 1 Mar. 1 Apr.
0 1 2 3 4
Chemical ozone loss
Approximate altitude (km)
1 Jan. 1 Feb. 1 Mar. 1 A
Ozone (p.p.m.v.)
NH 2010–11
NH 2004–05
NH 1999–2000
NH 1998–99
NH 1996–97
NH 1995–96
SH 2003
SH envelope
Ozone loss (p.p.m.v.)
Figure 4
Chemical ozone loss estimates. a, Chemical loss as a function of
time and potential temperature from passive subtraction of MLS and ATLAS
passively-transported ozone (initialized with December MLS data).
b, Chemical loss from ozone sondes in unmixed vortex air as a function of
‘spring equivalent potential temperature’
(black contours in a). Shading,
Antarctic range defined by 1985 (the first year with profile measurements
inside the ozone hole
) and 2003 (a recent year with a severe ozone hole). The
2003 Antarctic curve is shifted by six months minus 10 days because ozone
sondes that year predominantly sampled the outermost vortex, where ozone
loss begins earliest. c, Ozone at a spring equivalent potential temperature of
465K (white contour in a), near the level of maximum chemical loss. Shading,
the region below the minimum reached in the 1985 Antarctic ozone hole. In
April 2011 most soundings sampled the disturbed vortex edge; only two were
made in air uninfluenced by mixing (red dots). Error bars, 1s uncertainties
based on the scatter of individual ozone-sonde measurements. Line colours as
in Fig. 1; 1998–99 (a winter with no ozone loss) is shown in cyan. NH, Northern
Hemisphere; SH, Southern Hemisphere.
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Column ozone
Total column ozone is a predominant factor determining exposure of
Earth’s surface to ultraviolet radiation
. In the context of previous
Arctic winters, 2011 was truly remarkable: the fraction of the Arctic
vortex in March with total ozone less than 275 Dobson units (DU) is
typically near zero, but reached nearly 45% in 2011 (Fig. 5a). Because
of the dynamically-driven correlation between total ozone and lower-
stratospheric temperature
(Supplementary Discussion), the
abiding cold in 1997 and 2011 would have led to lower March total
ozone than in other Arctic winters even without chemical loss;
dynamical conditions in March–April 1997 particularly favoured
low total ozone
(Supplementary Discussion). In March 2011, however,
the area of low total ozone covered more than twice as much of the
vortex as in 1997, and the daily vortex ‘ozone deficit (Supplementary
Fig. 5a) was 30–50 DU larger, consistent with the greater chemical loss
(Fig. 4). Maximum 2011 vortex fractions of low ozone approached
those in early Antarctic ozone holes (Fig. 5a). The close correspond-
ence between the vortex and both low total ozone and the large Arctic
total ozone deficit (Fig. 5b, d) implies that low total ozone in March
2011 resulted primarily from chemical loss
Discussion). The ozone deficit in the Antarctic (Fig. 5e) shows a
maximum over 0–90u W, and a minimum over 90–200u E, reflecting
a vortex position in 2010 different to that in the reference state (which
is less robust than that for the Arctic). Differences in morphology deep
in the vortex are, however, minimal. The 2011 Arctic ozone deficit was
at least comparable to that in the 2010 Antarctic vortex core at an
equivalent time.
An echo of the Antarctic
In the absence of chemical ozone loss, downward transport during
winter results in a springtime maximum in total ozone; because this
transport is stronger in the Arctic, background ozone levels there are
,100 DU higher than those in the Antarctic
. Therefore Arctic
spring total ozone could, even after chemical destruction comparable
to that in an Antarctic ozone hole (commonly defined by values less
than 220 DU; refs 7, 12), exhibit only a weak maximum in total ozone
rather than a well-defined minimum. Examination of the long-term
ozone-sonde record in the Arctic shows that abundances near 250 DU
or less are well below typical autumn values, thus appearing as a ‘hole’
in total ozone. Dynamical processes can result in transient regions of
very low total ozone (Supplementary Discussion, Supplementary Figs
5, 6) and/or local minima in lower-stratospheric ozone profiles (for
example, via ozone-poor extra-vortex air transported into the polar
). For an interhemispheric comparison of chemical loss, it is
thus important to verify that observed Arctic ozone decreases were
primarily related to chemical, rather than dynamical, processes.
Figure 4 shows that the precipitous decline in Arctic ozone in
February–March 2011 resulted from chemical loss of similar mag-
nitude to that in the Antarctic in the mid-1980s. Observed ozone
between ,15 and 20 km altitude decreased to values matching the
minima in early Antarctic ozone holes and those reached at the cor-
responding time in some recent Antarctic winters (Figs 2j–l; 3f). In
late March–early April, most ozone-sonde profiles in the vortex had
mixing ratios less than 1 p.p.m.v., with values ,0.7 p.p.m.v. over an
approximately 2-km altitude region, and some dipping to 0.5 p.p.m.v.
(Supplementary Fig. 7). Minimum total ozone in spring 2011 was
continuously below 250 DU for ,27 days (Supplementary Fig. 5b),
with a maximal area below that level of ,2 3 10
(roughly five
times the area of Germany or California). Values dropped to ,220–
230 DU for about a week in late March 2011.
In these respects, chemical ozone destruction in the 2011 Arctic
polar vortex attained, for the first time, a level clearly identifiable as an
Arctic ozone hole. On the other hand, although the magnitude of
chemical depletion was comparable to that in the Antarctic, total
ozone values remained higher and, because the areal extent of the
Arctic vortex was much smaller (,60% the size of a typical
Antarctic vortex), the low-ozone region was more confined.
The Arctic winter stratosphere exhibits striking interannual vari-
ability. The past decade has included the four most dynamically active
(hence among the warmest) Arctic winters in the past 32 years (ref.
35) and now the two coldest winters with largest ozone loss
extending the previously noted trend of the coldest winters becoming
. Had implementation of the Montreal Protocol not curbed
the increase in stratospheric halogen loading, formation of an Arctic
ozone hole would have already become common even in moderately
cold winters
. Even with the lower anthropogenic halogen levels
actually reached, the potential for Antarctic-like ozone loss in the
Arctic in the event of a persistently cold winter–spring such as that
in 2010–11 has been recognized for decades
. Despite temperatures
that were generally far higher than those in Antarctic winter, Arctic
chemical ozone destruction in 2011 rivalled that in some Antarctic
ozone holes. The development of an Arctic ozone hole under condi-
tions only slightly more extreme than those in some previous Arctic
winters raises the possibility of yet more severe depletion as lower-
stratospheric temperatures decrease. More acute Arctic ozone
destruction could exacerbate biological risks from increased ultra-
violet radiation exposure, especially if the vortex shifted over densely
populated mid-latitudes, as it did in April 2011.
Our present understanding of what drives variability in the Arctic
winter stratosphere is incomplete. Stratospheric temperatures and
vortex evolution depend on the atmosphere’s radiative properties
and propagation of wave activity
, which are being modified by
increasing greenhouse gas concentrations. Day-to-day tropospheric
disturbances can lead to stratospheric warming or cooling, depending
Area(<275 DU) / Area(vortex)
1 Feb. 1 Mar. 1 Apr.
1 Aug. 1 Sep. 1 Oct.
a Vortex fraction of low total O
26 Mar.
26 Sep.
Column O
26 Mar.
26 Sep.
Column decit (DU)
Figure 5
Total column ozone. a, Time series of the fraction of 460 K vortex
area with total ozone below 275 Dobson units (DU) in February–April in the
Arctic (bottom axis), and in August–October in the Antarctic (top axis). Line
colours/shading as in Fig. 1. 2005–2011 values are from OMI; earlier values are
from TOMS (Total Ozone Mapping Spectrometer) instruments
. Maps show
OMI total ozone (b, c) and ozone deficit (d, e) in the Arctic (Antarctic) on
26 March 2011 (26 September 2010). Overlays as in Fig. 2 but at 460 K.
00 MONTH 2011 | VOL 000 | NATURE | 5
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on their geographical location and the stratospheric vortex structure,
which controls their upward propagation
. Current climate models
do not fully capture either the observed short-timescale patterns of
Arctic variability or the full extent of the observed longer-term cooling
trend in cold stratospheric winters; nor do they agree on future cir-
culation changes that affect trends in transport
. Our ability to
predict when conditions similar to, or more extreme than, those in
2011 may be realized is thus very limited. Improving our predictive
capabilities for Arctic ozone loss, especially while anthropogenic
halogen levels remain high, is one of the greatest challenges in polar
ozone research. Comprehensive stratospheric data sets, such as those
used here, are critical to meeting that challenge.
MERRA (Modern Era Retrospective-analysis for Research and Applications
fields are used for temperature and vortex analysis and for vortex averaging of
composition measurements. The CALIOP (Cloud-Aerosol Lidar with
Orthogonal Polarization) on the CALIPSO (Cloud-Aerosol Lidar and Infrared
Pathfinder Satellite Observations) satellite
provides PSC/aerosol information.
Trace gas profiles are from the Microwave Limb Sounder (MLS)
on NASA’s
Aura satellite. Only daytime ClO measurements are used. Northern (southern)
high latitudes are sampled near midday (in late afternoon), thus the average solar
zenith angle (SZA) of MLS Antarctic measurements is ,7u higher than that in the
Arctic. Reactive chlorine partitioning shifts away from ClO at higher SZAs
leading to ,30% lower ClO measured in the Antarctic than in the Arctic under
fully activated conditions. An instrument anomaly disrupted MLS measurements
from 27 March to 20 April 2011. UARS (Upper Atmosphere Research Satellite)
MLS measurements, used for 1995–1996 and 1996–1997 analyses, are sparse
because of the UARS yaw cycle and other measurement gaps
Total column ozone is measured by the Dutch-Finnish Ozone Monitoring
Instrument (OMI)
on Aura. Total ozone ‘deficit’ is the difference between daily
values and a reference that is minimally affected by chemical loss.
Measurements from MLS and the Match network of balloon-borne ozone
soundings (ozone sondes)
are used to estimate chemical ozone loss in two ways.
The difference between calculated ‘passive’ (influenced only by transport) ozone
and observed ozone is computed, with passive ozone obtained using MLS nitrous
, a ‘reverse trajectory’ model
, and the ATLAS (Alfred Wegener Institute
Lagrangian Chemistry/Transport System) model
. Vortex ozone is also examined
on the surfaces on which it subsides
, with descent rates from modelled
radiative heating/cooling rates averaged over the polar vortex
Photochemical box model runs were performed using the chemical model
from ATLAS
to test the sensitivity of ozone loss to initial ozone amounts and
Full Methods and any associated references are available in the online version of
the paper at
Received 3 May; accepted 7 September 2011.
Published online 2 October 2011.
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Supplementary Information is linked to the online version of the paper at
Acknowledgements We thank the MLS (especially A. Lambert, D. Miller, W. Read,
M. Schwartz, P. Stek, J. Waters), OMI (especially P. K. Bhartia, G. Jaross, G. Labow),
CALIPSO and Match science teams, as well as A. Douglass, J. Joiner and the Aura
project, for their support. We also thank W. Daffer and R. Fuller for programming
assistance at JPL; the many observers whose work went into obtaining the ozone-sonde
measurements; the ozone scientists who participated in the discussion of the 2011
Arctic ozone loss and appropriate definition of an Arctic ozone hole (including, but not
limited to, N. Harris, G. Bodeker, G. Braathen, M. Kurylo, R. Salawitch); and especially
P. Newman and K. Minschwaner for discussions and comments. Meteorological
analyses were provided by NASA’s Global Modeling and Assimilation Office (GMAO)
and by the European Centre for Medium-Range Weather Forecasts. We thank
S. Pawson of GMAO for advice on usage of the MERRA reanalysis. Ozone-sonde
measurements at Alert, Eureka, Resolute Bay, Churchill and Goose Bay were funded by
Environment Canada. Additional ozone sondes were flown at Eureka as part of the
Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaign and
were funded by the Canadian Space Agency. Academy of Finland provided partial
funding for performing and processing ozone-sonde measurements in Jokioinen and
. Ozone soundings and work at AWI were partially funded by the EC DG
Research through the RECONCILE project. Work at the Jet Propulsion Laboratory,
California Institute of Technology, and at Science Systems and Applications Inc., was
done under contract with NASA.
Author Contributions G.L.M. and M.L.S. led analysis of MLS data; M.R. led analysis of
ozone-sonde data; G.L.M. led the meteorological data analysis. M.R., G.L.M., N.J.L. and
I.W. did chemical ozone loss calculations. R.L. and M.R. performed and analysed
chemical box model calculations. M.C.P. and L.R.P. provided CALIPSO/CALIOP data
analyses; E.R.N. and P.V. provided TOMS and OMI data analyses. L.F., M.L.S., G.L.M. and
N.J.L. provided expertise on MLS data usage; D.P.H., P.V. and P.F.L. provided expertise
on OMI data usage. J.D., V.D., H.G., B.J., R.K., E.K., N.L., A.M., C.T.M., H.N., M.C.P., D.W.T.,
P.v.d.G., K.A.W. and N.S.Z. were responsible for performing and processing
ozone-sonde measurements. All authors contributed comments on the manuscript.
G.L.M., M.L.S. and M.R. jointly compiled and synthesized the results. G.L.M. and M.L.S.
wrote the paper.
Author Information CALIOP data are publicly available at
PRODOCS/calipso/table_calipso.html, MLS data at
data-holdings/MLS, OMI data at
OMI/omto3_v003.shtml, and GEOS-5 MERRA analyses through http:// The balloon-borne Antarctic
ozone-sonde data recorded in 1985 and the following years are publicly available at Reprints and permissions information
is available at The authors declare no competing financial
interests. Readers are welcome to comment on the online version of this article at Correspondence and requests for materials should be
addressed to G.L.M. ( or M.L.S.
00 MONTH 2011 | VOL 000 | NATURE | 7
Macmillan Publishers Limited. All rights reserved
Data sets. Modern Era Retrospective-analysis for Research and Applications
fields, from the Goddard Earth Observing System Version 5.2.0
(GEOS-5) data assimilation system, are used for the temperature and vortex
analysis. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on
the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations
(CALIPSO) satellite
provides PSC/aerosol information. CALIOP measure-
ments began in April 2006. Trace gas profile measurements are from the
Microwave Limb Sounder (MLS)
on NASA’s Aura satellite, and the predecessor
MLS instrument
on the Upper Atmosphere Research Satellite (UARS). Total
column ozone data are from the Dutch-Finnish Ozone Monitoring Instrument
on board Aura. The historical total ozone record comprises data from
Nimbus-7 and Earth Probe Total Ozone Mapping Spectrometer (TOMS)
. Aura
MLS and OMI measurements are available from August 2004 through to the
present. UARS MLS measurements were obtained from September 1992 through
to early 2000, with increasingly sparse sampling in the later years
. TOMS data
are available beginning in 1979, but no TOMS instrument was taking measure-
ments during the 1995–96 Arctic winter.
Measurements from the Match network of balloon-borne ozone soundings
(ozone sondes)
are used in some of the chemical ozone loss estimates.
Temperature and vortex analysis. Potential vorticity
(PV) is used to define
the vortex, with a contour of ‘scaled’ PV of 1.4 3 10
(in vorticity units)
demarking the vortex edge
. Vortex strength is diagnosed as the maximum
daily gradient in PV as a function of equivalent latitude (the latitude that would
enclose the same area between it and the pole as a given PV contour)
. Scaled
PV multiplied by 10
is used in the calculation, resulting in units for its gradient of
(s degrees equivalent latitude)
The temperature threshold for chlorine activation, T
, is estimated using the
formula for nitric acid trihydrate formation
, which depends on pressure, HNO
and H
O. Climatological HNO
and H
O profiles are used, derived from UARS
data. The area with T , T
is calculated on seven isentropic surfaces in the lower
stratosphere: 390, 410, 430, 460, 490, 520 and 550 K; T
on these levels is 197.5,
197.2, 196.8, 196.5, 195.9, 195.3 and 194.5 K, respectively. To get the volume with
T , T
from 380 through 565 K, the areas at each of the seven levels are mul-
tiplied by the estimated altitude associated with that layer and summed. The
altitude range associated with each layer is obtained from a standard potential
temperature profile as a function of altitude derived from high latitude temper-
ature soundings taken during the 1988–89 through to 2001–02 winters (the same
profile was used for V
calculations in refs 13, 16 and 48). These thicknesses are
1.29088, 1.19995, 1.36770, 1.46281, 1.30554, 1.18199 and 1.07382 km for the
seven levels listed above. Vortex volume is calculated from vortex area in the
same manner. Winter mean V
is calculated over 16 December through to 15
April. Previous studies have shown that V
scaled by the vortex area is a good
proxy for chlorine activation and ozone loss potential
. Additional temperature
and vortex diagnostics are described in Supplementary Information.
Polar stratospheric cloud and aerosol information. Particulate backscatter
averaged over the polar vortex derived from CALIOP data is used to provide
PSC/aerosol information. Total attenuated backscatter at 532 nm, b(z), is one of
the basic CALIOP Level 1B data products. b(z) is the sum of the particulate
backscatter (due to liquid aerosol and PSCs), b
(z), and molecular backscatter,
(z). b
(z) is calculated using GEOS-5 molecular density profiles (included in
the CALIOP Level 1B data files) and a theoretical value for the molecular scatter-
ing cross-section
. Profiles of b
(z) are then produced by subtracting b
(z) from
b(z). Vortex-averaged profiles of b
(z) are produced by averaging all CALIOP
(z) profiles located inside the vortex edge (defined using information available
in GEOS-5 Derived Meteorological Product (DMP) files for the nearly-coincident
Aura MLS data
) over the selected time interval.
MLS trace gas profile measurements and analysis. Trace gas profile measure-
ments of HNO
, HCl, ClO, ozone and N
O (a long-lived tracer used to assess
descent) are from Aura MLS
version 3 retrievals; data quality screening is as
recommended in the MLS data quality document
. MLS data are retrieved on
pressure surfaces; potential temperature as a function of pressure from MLS
calculated from GEOS-5 analyses is used to interpolate to isentropic
surfaces. Vortex averages of MLS data are calculated using the 1.4 3 10
scaled PV contour to define the vortex edge, using PV values from the MLS
. Active chlorine is in the form of ClO mainly during the daytime, and
thus measured ClO amounts vary with the solar zenith angle (SZA) at which the
measurements are taken. Only daytime ClO measurements are used here.
Northern high latitudes are sampled near midday local time, southern high
latitudes are sampled in late afternoon, thus the SZA of Aura MLS Antarctic
measurements is ,7u higher on average than that in the Arctic. Reactive chlorine
partitioning shifts away from ClO at higher SZAs
, leading to ,30% lower ClO
measured by Aura MLS in the Antarctic than in the Arctic under fully activated
conditions. MLS measurements are unavailable from 27 March through to
20 April 2011 because of an instrument anomaly. Upper Atmosphere Research
Satellite (UARS) MLS measurements, used for analysis of 1995–96 and 1996–97,
are sparse because of the UARS yaw cycle and other measurement gaps
. The
time of day of UARS measurements varied through the yaw cycle, in the middle of
which no daytime ClO measurements were obtained
; thus ClO values shown in
1995–96 and 1996–97 near those dates (including the mid-February 1996 mea-
surements shown in Fig. 2g) are not representative of the degree of chlorine
Chemical loss calculations. Chemical ozone loss is quantified by two methods,
both widely used for such calculations
. In the ‘passive subtraction’
, a transport model is used to calculate the evolution of ozone in
the absence of chemical changes (‘passive’ ozone). The difference between passive
ozone and observed ozone provides an estimate of chemical loss.
Here, passive ozone is obtained in three different ways. First, MLS observations
of N
O, a long-lived species unaffected by chemical processes, are used to cal-
culate vertical motion, and that estimate of descent is then used to calculate how
initial MLS ozone profiles would have evolved in the absence of chemical loss
Second, a ‘reverse trajectory’ transport model
is used to transport an initial
state based on MLS-observed ozone with no chemistry. Finally, the ATLAS
(Alfred Wegener Institute Lagrangian Chemistry/Transport System) chemistry
and transport model is run in passive mode
, initialized with MLS ozone.
Vortex ozone is also examined in relation to the surfaces on which it is sub-
. The descent rates used here are obtained by averaging radiative
heating/cooling rates from the radiation calculation used in the ATLAS model
over the polar vortex
. These rates are then used to examine vortex-averaged
MLS and ozone-sonde data on surfaces of ‘spring equivalent potential temper-
, defined as the potential temperature at which air originating at a given
level arrived at the end of March. Since the air descended on these surfaces, ozone
would have been constant on each such surface in the absence of chemical loss.
The ozone-sonde data used here are all from electrochemical concentration cell
(ECC) sondes, made by different manufacturers. Ozone-sonde data quality was
assessed in an intercomparison experiment
and is discussed in ref. 47. For
chemical loss calculations using ozone-sonde data, the profiles are first examined
using a procedure for detecting lamination in the profiles; such lamination (an
example is shown in Fig. 3f) is associated with mixing in of extra-vortex air, which
may obscure the signature of chemical loss. Profiles that have been significantly
altered by mixing processes, as indicated by lamination, are excluded from the
vortex averages used in the chemical loss calculations. 2010–11 Arctic ozone-
sonde data are provided as Supplementary Information.
Results from the ATLAS model passive subtraction calculations, and from the
calculations on spring equivalent potential temperature surfaces using the Match
network ozone-sonde data, are shown in Fig. 4; all panels show vortex averages.
These results have been compared with the results from the other methods
described above. While absolute ozone values obtained from different methods/
data sets vary significantly (up to ,0.4 p.p.m.v. at the end of March 2011), the
year-to-year variations in chemical loss calculated using all three methods agree
closely, indicating a high degree of precision in the relative amount of calculated
loss between different years.
The Alfred Wegener Institute chemical box model, also used as the chemical
module in ATLAS, simulates 175 reactions between 48 chemical species in the
This model was used to perform conceptual runs (Supplemen-
tary Fig. 4), started on 1 March with identical initial mixing ratios of all species
except HNO
and O
. For these two species values corresponding to 1997
(3 p.p.m.v. O
, 10 p.p.b.v. HNO
) and 2011 (2.2 p.p.m.v. O
, 6 p.p.b.v. HNO
(compare Figs 2a and 4c) were combined to yield four sets of initial conditions.
Initial ClO
was 2 p.p.b.v., corresponding to the vortex-averaged ClO
derived by
ATLAS from MLS ClO measurements on 1 March 2011. An air parcel at 70u N,
460 K potential temperature, with a temperature of 193 K throughout March, was
used. Heterogeneous reactions took place on liquid aerosols, rather than solid
(nitric acid trihydrate, NAT) PSCs, since the widespread existence of the latter is
inconsistent with MLS observations of gas-phase HNO
values (Fig. 2a) larger
than those the microphysical module predicts if NAT is present. A sensitivity
run showed that sporadically occurring solid PSCs did not change the results
Column ozone and ozone deficit calculation. OMI total ozone data were
processed with version 8.5 of the TOMS algorithm and have been extensively
. TOMS data were processed with version 8 of the algorithm. The OMI
and TOMS total ozone data used in this study were averaged on a fixed global
1u 3 1u latitude 3 longitude grid. Averages were computed by area-weighting
observations based on the overlap of their instantaneous field-of-view with each
grid cell. Only data that satisfy quality criteria based on measurement path length
and algorithm diagnostic criteria were included in the averaged samples.
Macmillan Publishers Limited. All rights reserved
Individual total ozone retrievals included in the samples are expected to have a
root-mean-squared error of 1–2%.
Total ozone ‘deficit’ is calculated as the difference between daily values and a
reference that is minimally affected by chemical ozone loss. The reference for the
Arctic is the daily mean over all Arctic winters from 1978–79 through to 2009–10,
from OMI starting in 2004–05 and from TOMS for earlier years
. The Antarctic
reference state is the daily mean of TOMS measurements for 1979 through to
1981. Because the Antarctic reference state is based on only three years’ data for
each day, variations in vortex position are not effectively averaged out; this
reference is thus less robust than that for the Arctic, so patterns in daily maps
may partially reflect differences in vortex position between the reference and the
focus day.
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2405–2408 (1994).
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products: Sampling issues and comparisons with Aura MLS. J. Geophys. Res. 112,
D24S50, (2007).
53. Butchart, N. & Remsberg, E. E. The area of the stratospheric polar vortex as a
diagnostic for tracer transport on an isentropic surface. J. Atmos. Sci. 43,
1319–1339 (1986).
54. Hanson, D. & Mauersberger, K. Laboratory studies of the nitric acid trihydrate:
implications for the south polar stratosphere. Geophys. Res. Lett. 15, 855–858
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Level 1 data products (Technical Report, NASA Langley Research Center, 2006);
available at Æ
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(Technical Report JPL D-33509, Jet Propulsion Laboratory, 2010); available at
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... A strong stratospheric PV leads to a decrease in temperature in the Arctic stratosphere, which contributes to the formation of polar stratospheric clouds involved in the activation of ozonedepleting substances, which leads to greater ozone depletion [28,29]. In the NH, the El Niño interaction with the stratospheric PV occurs through the Aleutian depression [18,30,31]. ...
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Tropical sea surface temperature (SST) variability, mainly driven by the El Niño–Southern Oscillation (ENSO), influences the atmospheric circulation and hence the transport of heat and chemical species in both the troposphere and stratosphere. This paper uses Met Office, ERA5 and MERRA2 reanalysis data to examine the impact of SST variability on the dynamics of the polar stratosphere and ozone layer over the period 1980 to 2020. Particular attention is paid to studying the differences in the influence of different types of ENSO (East Pacific (EP) and Central Pacific (CP)) for the El Niño and La Niña phases. It is shown that during the EP El Niño, the zonal wind weakens more strongly and changes direction more often than during the EP El Niño, and the CP El Niño leads to a more rapid decay of the polar vortex (PV), an increase in stratospheric air temperature and an increase in the concentration and total column ozone than during EP El Niño. For the CP La Niña, the PV is more stable, which often leads to a significant decrease in Arctic ozone. During EP La Niña, powerful sudden stratospheric warmings are often observed, which lead to the destruction of PV and an increase in column ozone.
... When the simulations are nudged to ERA5, the largest ozone reductions are simulated over the Arctic in the springs of 2011 and 2020 (7 and 5 DU zonal mean ozone loss, respectively, from Cl-VSLS in the April monthly mean). These larger ozone losses were facilitated by the formation of a particularly strong, cold and long-lasting polar vortex (Manney et al., 2011(Manney et al., , 2022Sinnhuber et al., 2011). We note that while very similar average large-scale ozone losses are diagnosed from the simulations nudged to different reanalysis products (Fig. 1c), some differences can emerge for individual regions and seasons. ...
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Depletion of the stratospheric ozone layer remains an ongoing environmental issue, with increasing stratospheric chlorine from very short-lived substances (VSLS) recently emerging as a potential but uncertain threat to its future recovery. Here the impact of chlorinated VSLS (Cl-VSLS) on past ozone is quantified, for the first time, using the UM–UKCA (Unified Model–United Kingdom Chemistry and Aerosol) chemistry-climate model. Model simulations nudged to reanalysis fields show that in the second decade of the 21st century Cl-VSLS reduced total column ozone by, on average, ∼ 2–3 DU (Dobson unit) in the springtime high latitudes and by ∼0.5 DU in the annual mean in the tropics. The largest ozone reductions were simulated in the Arctic in the springs of 2011 and 2020. During the recent cold Arctic winter of 2019/20 Cl-VSLS resulted in local ozone reductions of up to ∼7 % in the lower stratosphere and of ∼7 DU in total column ozone by the end of March. Despite nearly doubling of Cl-VSLS contribution to stratospheric chlorine over the early 21st century, the inclusion of Cl-VSLS in the nudged simulations does not substantially modify the magnitude of the simulated recent ozone trends and, thus, does not help to explain the persistent negative ozone trends that have been observed in the extra-polar lower stratosphere. The free-running simulations, on the other hand, suggest Cl-VSLS-induced amplification of the negative tropical lower-stratospheric ozone trend by ∼20 %, suggesting a potential role of the dynamical feedback from Cl-VSLS-induced chemical ozone loss. Finally, we calculate the ozone depletion potential of dichloromethane, the most abundant Cl-VSLS, at 0.0107. Our results illustrate a so-far modest but nonetheless non-negligible role of Cl-VSLS in contributing to the stratospheric ozone budget over the recent past that if continues could offset some of the gains achieved by the Montreal Protocol.
... The impermeability of this ETB is important, particularly for the springtime ozone depletion in the polar stratosphere known as "Antarctic and Arctic ozone holes" (e.g., Refs. [56,57] and references therein). Strong mixing occurs outside the polar vortex [54], where air parcels can travel long distances away from the vortex, forming complex patterns with stretching and folding. ...
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In the Lagrangian approach, the transport processes in the ocean and atmosphere are studied by tracking water or air parcels, each of which may carry different tracers. In the ocean, they are salt, nutrients, heat, and particulate matter, such as plankters, oil, radionuclides, and microplastics. In the atmosphere, the tracers are water vapor, ozone, and various chemicals. The observation and simulation reveal highly complex patterns of advection of tracers in turbulent-like geophysical flows. Transport barriers are material surfaces across which the transport is minimal. They can be classified into elliptic, parabolic, and hyperbolic barriers. Different diagnostics in detecting transport barriers and the analysis of their role in the dynamics of oceanic and atmospheric flows are reviewed. We discuss the mathematical tools, borrowed from dynamical systems theory, for detecting transport barriers in simple kinematic and dynamic models of vortical and jet-like flows. We show how the ideas and methods, developed for simple model flows, can be successfully applied for studying the role of barriers in oceanic and atmospheric flows. Special attention is placed on the significance of transport barriers in important practical issues: anthropogenic and natural pollution, advection of plankton, cross-shelf exchange, and propagation of upwelling fronts in coastal zones.
... Large seasonal ozone loss also occurs, albeit less frequently, in sufficiently cold Arctic springs (Manney et al., 2011(Manney et al., , 2020. Despite being relatively infrequent, Arctic ozone minima have a great societal relevance because of their potential impacts on health and climate (Norval et al., 2011;. ...
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In the Arctic stratosphere, the combination of chemical ozone depletion by halogenated ozone-depleting substances (hODSs) and dynamic fluctuations can lead to severe ozone minima. These Arctic ozone minima are of great societal concern due to their health and climate impacts. Owing to the success of the Montreal Protocol, hODSs in the stratosphere are gradually declining, resulting in a recovery of the ozone layer. On the other hand, continued greenhouse gas (GHG) emissions cool the stratosphere, possibly enhancing the formation of polar stratospheric clouds (PSCs) and, thus, enabling more efficient chemical ozone destruction. Other processes, such as the acceleration of the Brewer–Dobson circulation, also affect stratospheric temperatures, further complicating the picture. Therefore, it is currently unclear whether major Arctic ozone minima will still occur at the end of the 21st century despite decreasing hODSs. We have examined this question for different emission pathways using simulations conducted within the Chemistry-Climate Model Initiative (CCMI-1 and CCMI-2022) and found large differences in the models' ability to simulate the magnitude of ozone minima in the present-day climate. Models with a generally too-cold polar stratosphere (cold bias) produce pronounced ozone minima under present-day climate conditions because they simulate more PSCs and, thus, high concentrations of active chlorine species (ClOx). These models predict the largest decrease in ozone minima in the future. Conversely, models with a warm polar stratosphere (warm bias) have the smallest sensitivity of ozone minima to future changes in hODS and GHG concentrations. As a result, the scatter among models in terms of the magnitude of Arctic spring ozone minima will decrease in the future. Overall, these results suggest that Arctic ozone minima will become weaker over the next decades, largely due to the decline in hODS abundances. We note that none of the models analysed here project a notable increase of ozone minima in the future. Stratospheric cooling caused by increasing GHG concentrations is expected to play a secondary role as its effect in the Arctic stratosphere is weakened by opposing radiative and dynamical mechanisms.
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Long-term ground-based ozone measurements are crucial to study the recovery of stratospheric ozone as well as the trends of tropospheric ozone. This study is performed in the context of the LOTUS (Long-term Ozone Trends and Uncertainties in the Stratosphere) and TOAR-II (Tropospheric Ozone Assessment Report, phase II) initiatives. We perform an intercomparison study of total column ozone and multiple partial ozone columns between the ground-based measurements available at the Lauder station from 2000 to 2022, which are the Fourier transform infrared (FTIR) spectrometer, Dobson Umkehr, ozonesonde, lidar, and the microwave radiometer. We compare partial columns, defined to provide independent information: one tropospheric and three stratospheric columns. The intercomparison is analyzed using the median of relative differences (the bias) of FTIR with each of the other measurements, the scaled Median Absolute deviation (MADs), and a trend of these differences (measurement drift). The total column shows a bias and strong scatter well within the combined systematic and random uncertainties respectively. There is however a drift of 0.6±0.5 %/decade if we consider the full time series. In the troposphere we find a low bias of -1.9 % with the ozonesondes. No drift is found between the three instruments in the troposphere, which is good for trend studies within TOAR-II. In both the lower and upper stratosphere, we get a negative bias for all instruments with respect to FTIR (between -1.2 % and -6.8 %), but all are within the range of the systematic uncertainties. In the middle stratosphere we seem to find a negative bias of around -5.2 to -6.6 %, pointing towards too high values for FTIR in this partial column. We find no significant drift in the stratosphere between ozonesonde and FTIR for all partial columns. We do observe drift between the FTIR and Umkehr partial columns in the lower and upper stratospheres (2.6±1.1 %/decade and -3.2±0.9 %/decade), with lidar in the midle and upper stratosphere (2.1±0.8 %/decade and -3.7±1.2 %/decade), and with MWR in the midle stratosphere (3.1±1.7 %/decade). These drifts point to the fact that the different observed trends in LOTUS are not due to different sampling, vertical sensitivity or time periods and gaps. However, the difference in trends in LOTUS is reduced by applying a new FTIR retrieval strategy, which changes inputs such as the choice of microwindows, spectroscopy from HITRAN2008 to HITRAN2020, and the regularization method.
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The Arctic stratospheric ozone depletion event in spring 2020 was the most severe compared with previous years. We retrieved the critical indicator ozone vertical column density (VCD) using zenith scattered light differential optical absorption spectroscopy (ZSL-DOAS) from March 2017 to September 2021 in Ny-Ålesund, Svalbard, Norway. The average ozone VCD over Ny-Ålesund between 18 March and 18 April 2020 was approximately 274.8 Dobson units (DU), which was only 64.7 ± 0.1% of that recorded in other years (2017, 2018, 2019, and 2021). The daily peak difference was 195.7 DU during this period. The retrieved daily averages of ozone VCDs were compared with satellite observations from the Global Ozone Monitoring Experiment-2 (GOME-2), a Brewer spectrophotometer, and a Système d’Analyze par Observation Zénithale (SAOZ) spectrometer at Ny-Ålesund. As determined using the empirical cumulative density function, ozone VCDs from the ZSL-DOAS dataset were strongly correlated with data from the GOME-2 and SAOZ at lower and higher values, and ozone VCDs from the Brewer instrument were overestimated. The resulting Pearson correlation coefficients were relatively high at 0.97, 0.87, and 0.91, respectively. In addition, the relative deviations were 2.3%, 3.1%, and 3.5%, respectively. Sounding and ERA5 data indicated that severe ozone depletion occurred between mid-March and mid-April 2020 in the 16–20 km altitude range over Ny-Ålesund, which was strongly associated with the overall persistently low temperatures in the winter of 2019/2020. Using ZSL-DOAS observations, we obtained ozone VCDs and provided evidence for the unprecedented ozone depletion during the Arctic spring of 2020. This is essential for the study of polar ozone changes and their effect on climate change and ecological conditions.
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Ozone depletion by chlorofluorocarbons (CFCs) was first proposed by Molina and Rowland in their 1974 Nature paper. Since that time, the scientific connection between ozone losses and CFCs and other ozone depleting substances (ODSs) has been firmly established with laboratory measurements, atmospheric observations, and modeling research. This science research led to the implementation of international agreements that largely stopped the production of ODSs. In this study we use a fully-coupled radiation-chemical-dynamical model to simulate a future world where ODSs were never regulated and ODS production grew at an annual rate of 3%. In this "world avoided" simulation, 17% of the globally-average column ozone is destroyed by 2020, and 67% is destroyed by 2065 in comparison to 1980. Large ozone depletions in the polar region become year-round rather than just seasonal as is currently observed in the Antarctic ozone hole. Very large temperature decreases are observed in response to circulation changes and decreased shortwave radiation absorption by ozone. Ozone levels in the tropical lower stratosphere remain constant until about 2053 and then collapse to near zero by 2058 as a result of heterogeneous chemical processes (as currently observed in the Antarctic ozone hole). The tropical cooling that triggers the ozone collapse is caused by an increase of the tropical upwelling. In response to ozone changes, ultraviolet radiation increases, more than doubling the erythemal radiation in the northern summer midlatitudes by 2060.
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ATLAS is a new global Lagrangian Chemistry and Transport Model (CTM), which includes a stratospheric chemistry scheme with 46 active species, 171 reactions, heterogeneous chemistry on polar stratospheric clouds and a Lagrangian denitrification module. Lagrangian (trajectory-based) models have several important advantages over conventional Eulerian models, including the absence of spurious numerical diffusion, efficient code parallelization and no limitation of the largest time step by the Courant-Friedrichs-Lewy criterion. This work describes and validates the stratospheric chemistry scheme of the model. Stratospheric chemistry is simulated with ATLAS for the Arctic winter 1999/2000, with a focus on polar ozone depletion and denitrification. The simulations are used to validate the chemistry module in comparison with measurements of the SOLVE/THESEO 2000 campaign. A Lagrangian denitrification module, which is based on the simulation of the nucleation, sedimentation and growth of a large number of polar stratospheric cloud particles, is used to model the substantial denitrification that occured in this winter.
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This paper focuses on polar stratospheric cloud (PSC) measurements by the CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) lidar system onboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) spacecraft, which has been operating since June 2006. We describe a second-generation PSC detection algorithm that utilizes both the CALIOP 532-nm scattering ratio (ratio of total-to-molecular backscatter coefficients) and 532-nm perpendicular backscatter coefficient measurements for cloud detection. The inclusion of the perpendicular backscatter measurements enhances the detection of tenuous PSC mixtures containing low number densities of solid (likely nitric acid trihydrate, NAT) particles and leads to about a 15% increase in PSC areal coverage compared with our original algorithm. Although these low number density NAT mixtures would have a minimal impact on chlorine activation due to their relatively small particle surface area, these particles may play a significant role in denitrification and therefore are an important component of our PSC detection. In addition, the new algorithm allows discrimination of PSCs by composition in terms of their ensemble backscatter and depolarization in a manner analogous to that used in previous ground-based and airborne lidar PSC studies. Based on theoretical optical calculations, we define four CALIPSO-based composition classes which we call supercooled ternary solution (STS), ice, and Mix1 and Mix2, denoting mixtures of STS with NAT particles in lower or higher number densities/volumes, respectively. We examine the evolution of PSCs for three Antarctic and two Arctic seasons and illustrate the unique attributes of the CALIPSO PSC database. These analyses show substantial interannual variability in PSC areal coverage and also the well-known contrast between the Antarctic and Arctic. The CALIPSO data also reveal seasonal and altitudinal variations in Antarctic PSC composition, which are related to changes in HNO3 and H2O observed by the Microwave Limb Sounder on the Aura satellite.
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A comprehensive analysis of version 5 (V5) Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) ozone data using a Lagrangian transport (LT) model provides estimates of chemical ozone depletion for the 1991-1992 through 1997-1998 Arctic winters. These new estimates give a consistent, three-dimensional picture of ozone loss during seven Arctic winters; previous Arctic ozone loss estimates from MLS were based on various earlier data versions and were done only for late winter and only for a subset of the years observed by MLS. We find large interannual variability in the amount, timing, and patterns of ozone depletion and in the degree to which chemical loss is masked by dynamical processes. Analyses of long-lived trace gas data suggest that the LT model sometimes overestimates descent at levels above ~520 K, so we have most confidence in the results at lower levels. When the vortex is shifted off the pole and the cold region is near the vortex edge (e.g., late winter 1993 and 1996), most rapid ozone depletion occurs near the vortex edge; when the vortex and cold region are pole-centered (e.g., late winter 1994 and 1997), most ozone loss takes place in the vortex core. MLS observed the most severe ozone depletion in 1995-1996, with about 1.3 ppmv cumulative loss for the winter at 465 K by 3 March 1996; ~1.0 ppmv cumulative loss is seen at 465 K by mid-March 1993. Analyses of MLS data show significant ozone loss during January in most years, ranging from ~0.3 to 0.6 ppmv at 465 K. A modified LT model used with the limited MLS data in 2000 gives rough estimates of ~0.04 and 0.006-0.012 ppmv/day during 2-12 February and 12 February-29 March 2000, respectively, broadly consistent with other studies of the 1999-2000 winter. Estimates of depletion in MLS column ozone above 100 hPa are considerably smaller than other reported column loss estimates, primarily because many estimates include loss below 100 hPa and because MLS does not continuously observe the Arctic after early spring. Our results from analyses of MLS data confirm previous conclusions of broad overall agreement between many ozone loss estimates in the Arctic lower stratosphere near 450-480 K.
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This paper provides background material for a collection of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) algorithm papers that are to be published in the Journal of Atmospheric and Oceanic Technology. It provides a brief description of the design and performance of CALIOP, a three-channel elastic backscatter lidar on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. After more than 2 yr of on-orbit operation, CALIOP performance continues to be excellent in the key areas of laser energy, signal-to-noise ratio, polarization sensitivity, and overall long-term stability, and the instrument continues to produce high-quality data products. There are, however, some areas where performance has been less than ideal. These include short-term changes in the calibration coefficients at both wavelengths as the satellite passes between dark and sunlight, some radiation-induced effects on both the detectors and the laser when passing through the South Atlantic Anomaly, and slow transient recovery on the 532-nm channels. Although these issues require some special treatment in data analysis, they do not seriously detract from the overall quality of the level 2 data products.
During Arctic winters with a cold, stable stratospheric circulation, reactions on the surface of polar stratospheric clouds (PSCs) lead to elevated abundances of chlorine monoxide (ClO) that, in the presence of sunlight, destroy ozone. Here we show that PSCs were more widespread during the 1999/2000 Arctic winter than for any other Arctic winter in the past two decades. We have used three fundamentally different approaches to derive the degree of chemical ozone loss from ozonesonde, balloon, aircraft, and satellite instruments. We show that the ozone losses derived from these different instruments and approaches agree very well, resulting in a high level of confidence in the results. Chemical processes led to a 70% reduction of ozone for a region ∼1 km thick of the lower stratosphere, the largest degree of local loss ever reported for the Arctic. The Match analysis of ozonesonde data shows that the accumulated chemical loss of ozone inside the Arctic vortex totaled 117 ± 14 Dobson units (DU) by the end of winter. This loss, combined with dynamical redistribution of air parcels, resulted in a 88 ± 13 DU reduction in total column ozone compared to the amount that would have been present in the absence of any chemical loss. The chemical loss of ozone throughout the winter was nearly balanced by dynamical resupply of ozone to the vortex, resulting in a relatively constant value of total ozone of 340 ± 50 DU between early January and late March. This observation of nearly constant total ozone in the Arctic vortex is in contrast to the increase of total column ozone between January and March that is observed during most years.
The Modern-Era Retrospective Analysis for Research and Applications (MERRA) was undertaken by NASA’s Global Modeling and Assimilation Office with two primary objectives: to place observations from NASA’s Earth Observing System satellites into a climate context and to improve upon the hydrologic cycle represented in earlier generations of reanalyses. Focusing on the satellite era, from 1979 to the present, MERRA has achieved its goals with significant improvements in precipitation and water vapor climatology. Here, a brief overview of the system and some aspects of its performance, including quality assessment diagnostics from innovation and residual statistics, is given. By comparing MERRA with other updated reanalyses [the interim version of the next ECMWF Re-Analysis (ERA-Interim) and the Climate Forecast System Reanalysis (CFSR)], advances made in this new generation of reanalyses, as well as remaining deficiencies, are identified. Although there is little difference between the new reanalyses in many aspects of climate variability, substantial differences remain in poorly constrained quantities such as precipitation and surface fluxes. These differences, due to variations both in the models and in the analysis techniques, are an important measure of the uncertainty in reanalysis products. It is also found that all reanalyses are still quite sensitive to observing system changes. Dealing with this sensitivity remains the most pressing challenge for the next generation of reanalyses. Production has now caught up to the current period and MERRA is being continued as a near-real-time climate analysis. The output is available online through the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC).
The probability of polar stratospheric cloud (PSC) occurrence in the Antarctic and Arctic has been estimated using Stratospheric Aerosol Measurement (SAM) II aerosol extinction data from 1978 to 1989. Antarctic PSCs are typically observed by SAM II from mid-May to early November, with a maximum zonal average probability of about 0.6 at 18-20 km in August. The typical Arctic PSC season extends only from late November to early March, with a peak zonal average probability of about 0.1 in early February at 20-22 km. There is considerable year-to-year variability in Arctic PSC sightings because of changes in the dynamics of the northern polar vortex. Year-to-year variability in Antarctic sightings is most prominent in the number of late season clouds. Maximum PSC sighting probabilities in both polar regions occur in the region from 90 deg W through the Greenwich meridian to 90 deg E, where temperatures are coldest on average. Arctic sighting probabilities approach zero outside this region, but clouds have been sighted in the Antarctic at all longitudes during most months. Inferred PSC formation temperatures remain constant throughout the Arctic winter and are similar to those in early Antarctic winter. PSC formation temperatures in the Antarctic drop markedly in the 15 to 20-km region by September, a pattern consistent with the irreversible loss of HNO3 and H2O vapor in sedimenting PSC particles.
EOS MLS is an instrument that remotely senses Earth's upper troposphere, stratosphere and mesosphere by measuring millimeter and submillimeter wavelength thermal emission from the atmospheric limb. It will be operated on the EOS Aura satellite starting in 2004, and is a follow-on to the MLS on the Upper Atmosphere Research Satellite. New technology enables many more measurements by EOS MLS than were possible with UARS MLS, and measurements to lower altitudes. The EOS MLS measurement suite includes H2O, OH, HO2, O3, ClO, HCl, HOCl, BrO, N2O, HNO3, CO, HCN, CH3CN, volcanic SO2, temperature, cloud ice and geopotential height. All measurements are made day and night, simultaneously and continuously over 82S -82N latitudes on each orbit. Scientific objectives are to improve knowledge in areas of (1) stratospheric chemistry and chemistry-climate interactions, (2) upper tropospheric processes that affect climate variability, and (3) pollution in the upper troposphere. This talk will give an overview of the EOS MLS experiment.