JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 101, NO. D4, PAGES 8985-8999,APRIL 20, 1996
Decadal
evolution
of the Antarctic
ozone hole
Yibo JiangandYuk L. Yung
Divisionof GeologicalandPlanetarySciences,
CaliforniaInstituteof Technology,Pasadena
Richard W. Zurek
Earth and Space SciencesDivision, Jet PropulsionLaboratory,California Institute of Technology,
Pasadena
Abstract. Ozonecolumnamountsobtainedby thetotalozonemappingspectrometer
(TOMS) in the southernpolarregionare analyzedduringlate australwinter and
spring(days240-300) for 1980-1991usingarea-mapping
techniquesandareaweightedvortexaverages.The vortexhereis definedusingthe-50 PVU (1 PVU- 1.0
x 10-6K kg-1m2s'l) contour
onthe500K isentropic
surface.
Theprincipal
results
are: (1) thereis a distinctchangeafter 1985 in the vortex-averaged
columnozone
depletionrateduringSeptemberandOctober,theperiodof maximumozoneloss,and
(2) the vortex-averaged
columnozonein lateAugust(day240) hasdroppedby 70
Dobson units (DU) in a decadedue to the lossin the dark and the dilution effect. The
meanozonedepletionratein the vortexbetweenday 240 andthe day of minimum
1
vortex-averaged
ozoneis about1 DU d- at thebeginningof the decade,increasingto
1
about1.8 DU d- by 1985,andthenapparentlysaturatingthereafter.The vortexaveragecolumnozoneduringSeptemberandOctoberhasdeclinedat the rateof 11.3
DU yr-• (3.8%)from1980to 1987(90DU over8 years)andata smaller
rateof 2
DU yr-• (0.9%)from1987to 1991(10DU over5 years,excluding
theanomalous
year 1988). We interpretthe year-to-yeartrendin the ozonedepletionrate duringthe
earlierpart of the decadeas dueto the riseof anthropogenic
chlorinein the
atmosphere.
The slowertrendat the endof the decadeindicatessaturationof ozone
depletionin the vortexinterior,in that chlorineamountsin the mid-1980swere
alreadysufficientlyhighto depletemostof the ozonein air withinthe isolatedregions
of the lower-stratospheric
polarvortex. In subsequent
years,increases
in stratospheric
chlorinemay haveenhancedwintertimechemicallossof ozonein the southpolar
vortexevenbeforemajorlossesduringtheAntarcticspring.
I. Introduction
The presenceof thesechlorineradicals[de Zafra et al., 1987],
The dramatic decrease of the total column of ozone over
Antarcticain southernlate winterand spring(Augustthrough
November),a phenomenonknown as the Antarcticozonehole,
was first describedusing observationsmade with Dobson
spectrophotometer
on the ground [Farman et al., 1985] and
laterby satelliteobservations
[Stolarskiet al., 1986]. It is now
understood
that the Antarcticozonedepletionis causedby the
catalyticchlorinechemistryin the lower stratosphere,
where
low temperaturesprevail due to the special geographyand
meteorologyof the Antarcticregions(e.g., Plate 1). This cold
air in the lowerstratosphere
at high southernlatitudespermits
the formationand persistenceof polar stratospheric
clouds
(PSCs). Heterogeneous
chemistry[Solomonet al., 1986] on
theseice clouds,followedby the actionof sunlight,converts
particularly
of C10 andits anticorrelation
with 0 3, hasbeen
confirmedby in situ measurements
from aircraft[Andersonet
al., 1989a,b, 1991] andby remotesensingfrom the Upper
AtmosphereResearchSatellite (UARS) [Manney et al.,
1993b; Waters et al., 1993a, b]. While there is little doubt of
the key role played by heterogeneous
chemical reactions
involvingstratospheric
chlorine,thequantitative
aspects
of the
mechanismsinvolvedin producingthe Antarcticozonehole
are still the subjectsof intensestudyandobservation.This is
dueprincipallyto the effectsof dynamics
on the temperature
(andthusthe ice cloudmicrophysics)
andon the distributions
of chemicaltrace gasesand their exposureto sunlight
[Solomonet al., 1986; Bojkov, 1986; Mahlman and Fels,
1986; Tung et al., 1986; Garcia and Solomon, 1987;
Mcintyre, 1989; Solomon,1990; Schoeberlet al., 1991, 1992;
reservoir
species
of chlorine(HC1and C1ONO2)into very
reactiveradicalssuchasC1andC10 [McElroyet al., 1986a,b; Tung and Yang, 1994a, b; Yang and Tung, 1994]. These
attempts
to
Molina et al., 1987b; Toon et al., 1986; Tolbert et al., 1987]. effectsvaryfromyearto yearandthuscomplicate
interpretthe observed 30% to 60% decline in total column
ozoneamountsduringthe last decade.A thoroughdiscussion
Copyright1996by theAmericanGeophysical
Union.
of the Antarcticozonehole was given by Solomon[1988,
1990] and WorldMeteorologicalOrganization(WMO) [1988,
Paper number96JD00063.
0148-0227/96/96JD-00063
$05.00
1989, 1991].
8985
8986
JIANG ET AL.: ANTARCTIC
OZONE HOLE
In this paperwe examinethe recordof total columnozone 3. Area-Mapping Method
variationsobservedby the total ozonemappingspectrometer
The ozonearea-mappingmethodusedhere was described
(TOMS) over the period 1980 - 1991. Past analysesof the
by
Yung et al. [1990] and is similar to that used in area
Antarctic ozone depletion have tended to use the ozone
minimumvaluesor zonalaverageswhen examiningdecadal mappingof Ertel'spotentialvorticityon an isentropicsurface
trends [Bowman, 1985, 1988, 1990; Herman et al., 1991, [Butchart and Remsberg,1986; Baldwin and Holten, 1988].
byanycontour
valuegl*(• t)
1993; Krueger et al., 1992; Stolarski et al., 1991, 1992]. LetA(t,gl*)betheareaenclosed
Other analyseshave focusedon interannualvariationsin the of ozonecolumnabundance,as a functionof time (0 and
( • ) onthesurface
of theEarth.A convenient
unitfor
ozone minimum values and have found potentiallinks to position
phenomenaassociatedwith the Quasi-BiennialOscillation the areaboundby an ozoneisoplethis the areaof the southern
(QBO) [e.g., Garcia and Solomon,1987; Lait et al., 1989]. hemisphere,
2•R2 (R is theradius
ofEarth).Forcomparison,
More recently,Randel and Wu [1995] examinedtrends in the areas out to the Antarctic circle and 60øS latitude circle are
ozoneby first averagingTOMS data alongpotentialvorticity 0.079 and 0.13, respectively,while the area of the Antarctica
(PV) contoursin order to account for displacementand continent,includingthe ice shelf,is 5.5% of the area of the
longitudinalasymmetries
of the polarvortex. Anothernatural southernhemisphere.
coordinatefor thesepurposes
is ozoneitself. Here we will use
Sincetotalcolumnozonegenerally
changes
monotonically
the ozonearea-mappingtechniquefirst appliedto Antarctic outwardfrom a minimumin the interiorto the edgeof the
ozoneby Yunget al. [1990] to reexaminethe declineratesof polar vortex, an area increase(decrease)of a total column
Antarctic springtime column ozone from 1980 to 1991, ozoneisoplethwith time impliesthat the ozonehole (i.e., the
emphasizing
both generaland year-to-year
changesoverthat regionof lowestcolumnozone)is expanding
(shrinking).This
period. A key modificationof the previousapplicationof this resultholdsno matterwherethe centerof ozoneholeis. Thus,
techniqueis to constrainthe ozoneareamappingto the south to first order,this methodfiltersout planetary-scale
(i.e., low
polar vortex using values of PV derived from National longitudinal
wavenumber)
perturbations
of theAntarcticpolar
MeteorologicalCenter(NMC) datafor thesameperiod.
vortexsuchas distortions
of thevortexor displacements
away
In section2, we first briefly describethe data we used.The from the pole. We assumethat the ozonecolumnabundance
area-mappingmethod is describedin section3. Then, in in the southpolar night regionis smallerthan that in the
section4, we presentour main results obtainedfrom the daylightregion and only include daytimedata in the area
TOMS ozone data using the area-mappingmethod in averages,
adjusting
theareaweightingto includejustthesunlit
combinationwith the use of PV and of area-mapped
NMC portionsof thesouthpolarregions.This haslittle effecton our
temperaturesin the polar vortex. Two importantfeatures analyses
aswe focusonthelatewinterandspringperiodwhen
emergingfromthe analysisarea distinctchangein the decline the area with no TOMS measurements
is very small (e.g.,
rate of vortex-averagedcolumn ozone after 1985 and the Plate 1).
anomalyrepresented
by the 1988Antarcticspring.
The assumptionof monotonic variation breaks down
beyondthe edgeof the polar vortex,in the regionof the total
columnozonemaximain high midlatitudessometimescalled
2. TOMS Ozone Column Abundance,PV and
the polar "collar"region. For somecontoursnear the vortex
Temperature
boundary,area-mappingwould mix data pointsfrom outside
The Nimbus 7 spacecraftwas launchedinto a local-noon, of the vortex with that inside the vortex. Vortex-averaged
Sun-synchronous,
near-polarorbit on October24, 1978. Its quantitieshave been shownto be useful in examiningthe
TOMS instrumenthas measuredthe spatial distributionof relationships
among,for instance,ozone,temperature
andC10
total ozonefrom 1978 until May 6, 1993, by scanningacross at variousheightsin the lower stratosphere
[e.g., Manney et
the track of the satellite to obtain data between successive
al., 1994b]. Randel and Wu [1995] recentlymappedcolumn
satellite orbital tracks. Total column ozone is retrieved from
ozoneby averagingtheTOMS dataaroundPV contours
at 520
the measured differential absorption of backscattered K. The issueis how to applya vortexconstraintgiventhat a
ultraviolet irradiance using observationstaken with solar definitionof thepolarvortexin termsof PV contours
will vary
zenith anglesup to 88ø. No measurements
are availablein with heightandfrom yearto year.
regionsof polar night. In our analysiswe used the daily
Becausethetotalcolumnozonevalueis heavilyweightedto
TOMS gridded ozone data of version 6.0 [Herman et al., thelowerstratosphere
[ e.g.,Manneyet al., 1994a;Froidevaux
1991] from NASA (on a 1ø x 1.25ø grid in latitude and et al., 1994], we have chosento definethe vortexusingPV
longitude)from 1980 to 1991. The 1979 datawerenot usedin valuesthere. By inspectionwe have chosena singlevalue,
our analysismainlydue to frequentlymissingdata (e.g. days namely,-50
PVU (1 PVU=I.0 x 10'6 K kg'l m2 s'l). In later
277, 278, 279) in this year. The more recentversion7 with years (1992 and 1993, not consideredhere), Chen [1994]
datacoverage
till 1994hasnotbeenofficiallyreleased
yet.
foundthatthisvalue,whichwas towardthe polewardedgeof
The othertwo data setsusedare NMC temperatures
and the region of large PV gradients,definedan isolatedinner
Rossby-ErtelPV [Manney and Zurek, 1993a] derivedfrom vortexat 500 K. For the yearsand seasonconsidered
herethe
NMC analysesof temperature
and geopotential
heights[e.g., -50 PVU contouris typicallyin the middle of the regionof
Gelman et al., 1986]. The PV and temperaturefields are strongPV gradientson the 500 K isentropicsurfaceand is
griddedat 2.5ø x 5.0ø in latitudeand longitude.In our study outsidetheregionof largeozoneloss(Plate1), whichmakesit
we will usetemperature
andPV fieldson the500 K isentropic suitablefor limiting the ozone area-mapping. Interannual
surfaceto help interpretvariationsin the total columnozone. variationsof the areawithin thisPV contourarerepresentative
This level is in the lowerstratosphere
nearthe ozonenumber of changesin vortex size and reflect at least indirectly
densitypeak in earlyAugust,priorto the formationin recent variations in planetary wave activity, including minor
yearsof theozoneholeduringtheaustralspring.
warmings; these can affect both ozone transport and
JIANG ET AL.: ANTARCTIC
heterogeneouschemistry. To assess these effects more
quantitativelyrequiresconsiderationof vertical as well as
horizontalvariationsin bothozoneand PV and is beyondthe
scopeof thispaper.
OZONE HOLE
8987
constrainedby the locationof the -50 PVU contourat 500 K.
The time intervalchosenfor eachyearis fromday 240 (August
28 for nonleapyear)to day 300, corresponding
to theperiodof
maximum ozone depletion in each year. These vortexconstrainedarea averagesof columnozoneare significantly
largerthan the minimumozonecolumnabundance[e.g., Lait
et al., 1989, Figure 2a], as they includelarge regionsof the
vortexcloseto the boundary,where ozonevaluesare higher
4. Area Mapping of Ozone, PV, and
Temperature' Results and Discussion
4.1. Average Column Ozone: The Ozone Hole Period
(Plate 1).
The dotted lines in Figure 1 indicatesthe area-weighted
We will first investigatevariationsof area-averaged
ozone
columnabundance
insidethepolarvortex.Figure1 showsthe averageof ozone column abundancein the region between
temporalvariationsof the area-weightedaverageof ozone 60øS and 90øS. Differences between this zonal and the vortexcolumn abundanceinside the polar vortex (solid line), as limitedaveragereflectthe longitudinal
asymmetry
of thepolar
.
180'
0
100
150
200
250
300
550
Colurn_nOzone (DU)
Plate 1. Southernpolarorthographic
projectionof ozonecolumnabundance(DU) on day 275 (October2)
1987. Thereareno TOMS datain the whitearea. The areaboundby the 300-DU contouris 13% of the area
of the southernhemisphere. The smaller and larger circles are located at 60øS and 30øS latitudes,
respectively. The thick red line indicatesregionswhere the temperatureis below 195 K on the 500 K
isentropicsurfaceandpolarstratospheric
clouds(PSCs)mayform. The -50 PVU contourof potentialvorticity
(PV) (thickdarkline) at 500 K, usedto definethepolarvortex,is alsoshown.
8988
JIANG ET AL.: ANTARCTIC
OZONE
I October
350 I Septernber
I October I Septernber
272
HOLE
274
280
271
268
276
278
277
263
276
274
278
1980
300
-''''' "•
350
•
/ \
z
''" "
\
"
25O
300
ß,
.
.
ß
....
.
,
\
\/
/
/x
xl
I
\
\/
/\
t•
\
-2_(3
\
,
..
\
z
2OO
350
-30
cO
z
300
o
250
N
o
z
-40
•
D
250
o
200
200
D 350 1984
810 ....
1985
815
90 '
-5o
YEAR
i,i
300
z
t•
250
z
< 200
z
350
1987
1986
300
Figure 2a. The area-weighted average ozone column
abundance(DU) on day 240 of eachyear (dottedcurve);same
for the minimumvalueattainedin eachyearbetweendays240
and 290 (solid curve). Dashedline givesthe percentlossof
ozone(relativeto day 240). The dayson which the minimum
value for the area-weightedaverageozonecolumnabundance
occurred are indicated.
o
250
z
o
200
N
O 35o 988
1989
dynamicallyactive [Krueger et al., 1989; Schoeberlet al.,
1989; Kanzawaand Kawaguchi,1990]: the vortexand ozone
holewere,by southern
hemisphere
standards,
often.greatly
300
distorted
anddisplaced
awayfromthe geographic
southpole.
By contrast,
thepolarzonalandvortex-averaged
columnozone
averages
areremarkablysimilarin 1987and 1989,indicating
thatin thoseyearsthevortexwasnearlyzonallysymmetric
and
250
200
350
1991
1990
300
extended at least to 60øS.
Similar differences
extendto otheryearsas well, with the
polar zonal and vortex area-weighted
averagesof column
ozoneagreeingmore closelyin Septemberduringodd than
duringevenyears. Furthermore,as seenin Plate2, the vortex-
•
i
i
.
i
,
i
.
,
i
.
i
,
i
,
,
i
200
.
limitedaverageof columnozonetendsto decrease
significantly
from 1981 to 1982 and 1983 to 1984, but with the column
ozoneaveragesrelativelyunchangedfrom 1980 to 1981, 1982
to 1983, and until October1984 to 1985. A differentpattern
Figure 1. Area-weightedaverageozone column abundance followsin 1986, with ozoneaveragevaluessimilarto thosein
(DU) insidethe polarvortexboundby PV contourof-50 PVU
1985. These are followed by a significantdecreasein
from days 240 to 300 for 1980 - 1991. Dotted lines denote
increased
valuesin
area-weighted average ozone column abundance (DU) September-October1987but substantially
1988,whenvortex-limited
columnozonevaluesareashighor
between 60øS and 90øS.
higher than those for the same monthsin 1984. After the
anomaly of 1988 the vortex-limitedozone averageagain
vortex and its seasonaldecreasein area during southern declines,with the lowestaveragedvaluesoccurring
in October
spring. The latteris evidentas a tendencyfor the zonaland 1991. In Septemberthe years 1990 and 1991 are reminiscent
vortexdelimitedaveragesto separateafterSeptember.As the of the patternin vortex-limitedaveragedcolumnozonebefore
vortexshrinksseasonally,
the zonalaverageincludesmoreof 1986. The lowest vortex-averaged
ozonecolumn abundance
240
250
260
270
DAY
280
290
3•0
250
260
270
280
290
300
DAY
the higherozonevaluesoutsidethe vortex. The short-periodoccurs in 1991. This result is consistent with that based on an
fluctuations
(i.e., of theorderof a few to severaldays)aremore analysisof the ozoneminimumvaluein October[Kruegeret
pronouncedin the high-latitudezonal average.Similar but al., 1992]. Hofmannet al. [1992] arguedthat the penetration
smaller amplitudefluctuationsappear in the vortex-limited of volcanicaerosols
fromPinatuboandHudsoninto the polar
area-weighted column ozone. These fluctuations, often
correlatedwith those of the zonal average,suggestthat
synoptic-scaledisturbancesof the vortex, of ozone in the
vortex,or of both are not filteredout by averagingwithin the
vortexmight haveenhancedthe depletionof ozone. However,
Schoeberlet al. [1993] showedthat the polarvortexand the
midlatitude regions were nearly isolated from each other
duringthe late Augustperiod. The issueof what causedthe
vortex.
unusuallylow ozonein 1991 remainsunresolved.
Both averages show the decline of column ozone in
Figure2a showsthe vortex-averaged
valueof columnozone
September-Octoberoverthe lastdecade.The years1986 and on day 240, the minimumvaluebeforeday 290 (mid-October),
1988 are notable in that the 60øS latitude and vortex-limited
and the day on which the minimumoccurredfor eachyear.
averagesdiffer even in early September. Theseyearswere As seenhere and in Table 1, the minimumvortex-averaged
JIANG ET AL.: ANTARCTIC
OZONE HOLE
8989
z
o
0.5 8•0 ....
815
,
9•0 ,
80
85
9•0
YEAR
YEAR
Figure2b. Meanozonecolumndepletion
rate(DUd -1)in the
polarvortex. The solidline denotes
the ratecomputed
using Figure 2c. The relativerate of ozoneloss in October(solid
line) as estimatedusing the model of Sanderet al. [1989].
ozonevalueson day 240 andthe dayof minimumozone. The
dashedline is basedon a 5-dayaverageof the initial valueof
ozonefrom days 240 to 244. The dottedline is basedon a
Thetotalchlorine
(Cly)in thestratosphere
from1980to 1990
240 and the day of minimum ozone. Details are summarized
proportional
to CI_andClv2,respectively.
All values
are
is taken from the model of Weisenstein et al. [1992].
The
linearleastsquares
fit to theaverage
ozonevaluesbetween
day dashedand dottedlines give the rate of ozonelossif it were
in Table 1.
columnamountoccurred
in all yearsduringthelastweekof
September
andthefirstweekof October,exceptfor 1988 when
it occurrednearlya weekearlierin mid-September.
The divergenceof the day 240 and the minimum value
curvesindicatesthat the averageloss of ozone during this
seasonearly in the decadeis abouthalf that at the end of the
decade,except for the anomalousyear 1988. The "initial
value" of vortex-averagecolumn ozone on day 240 has
declinedby 20% overthe decade. Recentobservations
by the
Microwave Limb Sounder(MLS) onboardUARS of higher
C10 and lower ozone as early as mid-July [Waters et al.,
1993a, b; Santee et al., 1995] indicate that some chlorine
activation and photochemicalozone loss occur in southern
midwinter.The depletionof ozoneat this earlytime (while the
geographicsouthpole is still in the dark) can occurbecause
the southpolarvortexis sufficientlylargethat its outerregions
are in sunlightevenduringthe periodof polarnight. Air there
may be exposedto polar stratosphericclouds in the same
regionsor can moveinto the sunlitregionsfollowingexposure
to PSCs in areasof polar night. The ensuingchemicallossof
ozone in the sunlit portionsof the vortex due to chlorine
photochemistry
couldaccount,then,for the downwardtrendof
vortex-average
columnozoneat theendof August.
Figure 2b showsthe decadalvariationin the mean ozone
depletionrate from day 240 to the day when the minimum
area-averaged
columnozoneis foundin the polarvortex(solid
normalized
tothat
Df1980,
the
year
with
Cly
=1.44
ppbv.
relatedto the computationof variousrates is summarizedin
Table 1. The depletion rates are particularly difficult to
estimatein 1988 and 1990, becausethe variationduring the
seasonis more nonlinearin thoseyears(Plate2).
The likely explanationfor the rapid increasein the ozone
depletion
rateis therapidriseof totalchlorine
(Cly)in the
lower stratospherein the early part of the decade. The
dominant effect of chlorine chemistry on ozone loss is
quadraticin C10 [Molina and Molina, 1987a; Sander et al.,
1989; Anderson et al., 1991], with smaller contributionsfrom
coupling
to bromineandHOx chemistry.
Thelattereffectsare
linear in C10. Figure 2c (solid line) showsthe rate of ozone
loss(relativeto 1980) as estimatedusingthe modelof Sander
etal. [1989].Thevalues
ofClyin thestratosphere
aretaken
from a model [Weisensteinet al., 1992], which is basedon the
releaseof chlorofluorocarbons,
atmosphericobservations,and
modeling. This showsthat the chemicalforcingon the ozone
hole has increasedfrom 1980 to 1985 by about40%, which is
about60% of the increasein ozonedepletionrate in the same
period(seeFigure 2b). For comparison,we alsocomputethe
chemical
forcing
if it werelinear
in Cly.!dashed
line)or
quadratic
in Cly(dotted
line).TheBrOm•mng
ratiowasset
equalto 5 (pptv) in all thesecalculations[Sanderet al., 1989].
We shouldpoint out that despitethe dominanceof theMolinaMolina catalyticcyclethat is quadraticin C10, the chemical
forcing
is notquadratic
in C1
Thereason
is thatasCly
y'
line). In the first threeyearsthe ozonedepletionrate during increases,part of the reactivechlorineis sequestered
in the
thisSeptember-October
periodis onlyabout1 DUd -1. After C1202 dimer,thuslowering
itsefficiency
forthedestruction
of
1982theozonedepletionrate increases
to a valueof 1.8 DU d-
ozone.
1 in 1985.Sincethen,theozonedepletion
ratehasfluctuated After 1985 the depletion of ozone apparentlyreached
around
1.5DUd -• andshows
a possible
QBOsignature.
The saturation,in that the ozone depletionrates did not increase
dashedline in Figure2b is obtainedin the sameway as for the
solid line, exceptthat the meanof 5 days(days240 - 244) is
usedfor the initial value. The dottedline is obtainedby using
a linear least squaresfit to the data. Detailed information
with increasingchlorineand,in fact, were probablymoderated
in later years by dynamical processes. These could
horizontallymodulatethe regionof photochemicallosswithin
the vortex(i.e., the chemicallyperturbedregion)or the areaof
8990
JIANG ET AL.: ANTARCTIC OZONE HOLE
September Octob,er
•so.I.. ,SepteTber
I Octob,er
ß
'
ß ß '
'
ß '
ß I
ß '
ß '
!
'
ß '
ß
ß ß ""
'
<•
r•
Z
ß
ß
i•
ß t
z
ß
ß
ß
t
ßß ßß i •1ß
o
iii ßß
250
ß
ß
.,
z
o
#
N
o
•
t
e
i
........
........
200
........
ß ,i
240
........
1980
1981
1982
.19•
i
........
.......
........
•1991
1984
i
I,i,i
250
1986
1987
191•
1989
1990
•
i
I
260
i
i
,
ß
I
....
270
I
280
....
I
290
i
....
•
DAY
240
i
i
i
I
250
i
i
i
ß
!
260
....
I
....
270
!
280
....
I
....
290
300
DAY
Plate 2. Alternativedisplayof thesolidlinesfromFigure1. The solidlinesarefor theoddyears;thedotted
lines are for the even years.
the vortex itself; they could also affect the rate of vertical
motion and so the seasonaldownwellingof air with higher
ozonemixing ratiosfrom the middlestratosphere
in the polar
vortex[Manneyet al., 1995].
The moderateddepletionrate after 1985 for columnozone
may alsobe dueto the factthatthe lossrate dependson ozone
itself, and ozoneamountsduringthis later periodare already
verylow duringthis season.This effectcanbe illustratedby
dividing for each year the differencebetweenthe day of
minimumvortex-averaged
columnozoneand day 240 by the
vortex-averaged
amounton Day 240. As seenin Figure 2a
(dashedline), the 1985 loss rate is sustainedin later years,
with 1988 againbeinga mostexceptionalyear.
We can comparethe lossratesof the vortex-average
areaweightedcolumnozoneof Figure2b to thosecomputed
by Lait
et al. [1989]. They usedthe minimumTOMS columnozone
value found polewardof 30øS on any given day to estimate
lineardeclineratesD for the late Augustto Septemberperiodß
They thenestimatedthechangeoverthe period1979 - 1987 by
leastsquaresfittingof the Septembervariationsandobtained:
D [DUd'l] =-0.19(year-1980)- 0.65
This canbe comparedto comparable
linearleastsquares
fitting
of the valuesshownin Figure2b for 1980- 1987'
D [DUd'l] = -0.14(year-1980) - 0.71
As noted above, the distinctchangein declinerates for the
vortex-averaged
column ozoneoccursafter 1985. A linear
leastsquaresfitting for the September
declineratesfor 1980 1985 yields
D [DU d'l] = -0.25(year
- 1980) - 0.51
JIANG ET AL.: ANTARCTIC
OZONE HOLE
8991
Table1. Column
Ozone
Depletion
Rate(DUd-1)AsComputed
byThreeMethods
Method la
Year
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
gl (DU)
(240)
324
332
297
309
288
289
286
271
283
271
256
259
gl (DU)
(Minimum)
293
291
261
262
241
225
233
214
251
217
213
198
Day of
Minimum
Method2b
Depletion
Rate
272
274
280
271
268
276
278
277
263
276
274
278
1.06
1.20
0.92
1.55
1.73
1,81
1.26
1.57
1.35
1.59
1.27
1.70
gl (DU)
(240)
320
323
293
303
288
292
277
269
289
266
251
262
Method3c
Depletion
Rate
0.90
0.98
0.85
1,37
1.70
1,83
1.09
1.49
1.65
1.42
1.11
1.75
Depletion
Rate
0.76
0.64
0.63
1,36
1.74
1.73
1.14
1.55
1.45
1.50
0.84
1.76
Meancolumn
ozone
depletion
rate(DUd-]) inthepolarvortex.
a Method 1 usesozonevalueson day 240 andthedayof minimumozone.
b Method
2 isbased
ona5-dayaverage
oftheinitialvalueofozone
fromdays240to244.
c Method3 is basedon a linearleastsquaresfit to the ozonevaluesbetweenday 240 and the day of minimum
ozone.
whichtranslates
into an increaseoverthoseyearsby a factorof
3 or more. This wouldreduceto a factorof 2 usingthe decline
ratescomputedin Figure 2b as simpledifferences.Both of
thesefactorsare largerthan that suggested
by the growthin
stratospheric
chlorine(Figure2c).
Lait et al. [1989] foundthat the residualsof the September
mappingtechniqueis used to examinethe evolutionof the
ozonehole in more detail. Plate 3 showsthe area enclosedby
contoursof ozone column abundance,again plotted versus
enclosed
areain unitsof 2nR2. Asbefore,
theperiodcovered
is from days 240 to 300 for 1980 - 1991, and the domainof
integrationis confinedinsidethepolarvortexby PV contourof
decline rates of minimum column ozone values from the
-50 PVU at 500 K. In these plots we have used 5-day
interannual
linearfit showeda distinctQBO signature.This is smoothingto remove high-frequencyvariations. Since there
consistentwith the Septemberdecline rates of the vortex- are no ozonedata for the part of the vortex in the dark, the
averagedcolumnozoneshownin Figure2b for yearsbefore bottomleft partsof thesefiguresareblank. Note thatthe areas
1986,exceptfor 1984. Oscillations
in September
declinerates boundedby columnozonecontourslessthan 250 DU increase
after 1985 havethe characterand magnitudeof thoseduring
Septemberin 1980 - 1982. However,the distinctiveQBO-like
patternshownin Plate 2 for vortex-averaged
columnozonein
1980 - 1985 is not apparentin lateryears.
Figure 3 showsthe vortex-average
area-weightedcolumn
ozonefor the periodwhenthe ozoneholeis deepestfrom 1980
to 1991. The changein trendfrom year to year for the years
beforeand after 1986 is clearlyseen,as is the anomalyof the
1988 column ozone variation. The area-averagedozone
columnabundancedecreases
with a slopeof 3.8% (11.3 DU)
peryearbefore1987and0.9% (2.0 DU) peryearafterthat(the
year 1988 is anomalous and is not included in the trend
analysis).The averagerate of declineis 25% per decadefrom
1980 to 1991. Theseratesof declineof the vortex-averaged
column ozone during one month (mid-September
to mid80
85
90
October)of lowestozonemay be comparedto the value30%
YEAR
per decadeobtainedon the basis of zonal averagesin the
southernpolar regionsfrom 1979 to 1990 [Herman et al., Figure3. The vortex-averaged
area-weighted
columnozone
3OO
250
1993]; similar rates of decline were also obtained when
abundance
(DU) in thevortexfromdays260 to 290 (mid-
columnozonewas mappedas a functionof PV within the Septemberto mid-October),the seasonof minimumcolumn
Antarcticpolar vortex for Septemberover the same period ozoneeach year. The steepdottedline is the linear least
[Randel and Wu, 1995]. However, the distinct break in trend squaresfit to the dataduringthismonthfrom 1980 and 1987.
Theslope
is 3.8%(11.3DU) peryearwiththeaveraged
ozone
after 1985hasnot beenpreviouslynoted.
value300 DU duringthistimein 1980asreference.The less
steepdottedline is a similar fit to the data from 1987 to 1991
4.2. Growth of the Ozone Hole
butexcluding
1988.Theslopeis 0.9%(2.0DU) peryearby
The resultspresentedaboveutilizedarea-weighted
averages usingthe averaged
ozonevalue222 DU duringthistimein
of columnozoneover the entirepolar vortex. Here the area- 1987.
8992
JIANG ET AL.: ANTARCTIC OZONE HOLE
•
d
•
d
v'•yv
•
o
V3•lV
V•lV
JIANG ET AL.: ANTARCTIC
rapidly aroundday 260 (mid-September),
implying that the
ozonehole is expandingand the columnozoneis decreasing
insidethe vortex. By day 280 (early October)the ozonehole
has reachedits greatestextentand depth. Typically,the area
remainsconstantthenfor a few daysbeforeit beginsto shrink.
This reflectsfirst the warmingof the vortexair and eventually
the seasonalweakening of the vortex itself, which has
generallybrokenup by November.
OZONE HOLE
272
277
275
8993
265
266
276
271
282
267
265
274
274
0.12
-61.6
0.08
-66.9
o o4
-73.7
As can be seen from Plate 3, the ozone column abundance
contourof 200 DU doesnot appearuntil 1983 but occupiesa
maximumareaof 7% of the southernhemisphere
in 1991. The
150-DU contourappearsin 1987. These regions are well
inside the polar vortex. On the vortexboundary,where the
ozonecolumn abundanceis usuallygreaterthan 300 DU, the
seasonalchangeof areareflectsthe areaof the vortex. In this
region (e.g., the 300-DU contour)there is a little increase
duringthe seasonalformationof the ozonehole,but mostlythe
areais constantuntil the vortexbeginsto decreasein area. As
seenin Plate 3, the ozonehole developsduringlate Augustto
mid-Septemberand is largely independentof day-to-day
variationsnearthe vortexboundary.Thesedifferenttrendsand
the generalsteepeningof the gradientsat the vortexboundary
0
-90.0
80
85
90
YEAR
Figure 4. The maximumarea (dots)enclosedby the 250 DU
contourin eachyearbetweendays260 and 300. The dayson
which
the maximum
area is attained
are indicated.
Also
shown for the same days are the areas of the vortex, as
indicatedby the -52 PVU contour(opencircle) on the 500 K
isentropicsurfaceandof the 195 K isotherm(plus),alsoat 500
K. The equivalentlatitudeis indicatedin the right-handaxis.
indicate that the air within the vortex is isolated in the lower
stratosphere
from air at similar levelsoutsidethe vortex. The
steepeningof ozonegradientsat the vortexboundaryresults
from the spatial expansionas well as the deepeningof the
ozoneholeoverthatperiod.
The anomalous behavior of 1988 is clearly seen by
comparingthe areasbound by the 200-DU contourin the
successive
years1987, 1988, and 1989. The maximumareas
in 1987 and 1989 exceed6% of the southernhemisphere,
whereasin 1988 the maximum area is only about 2% of the
southernhemisphere. Similar area mapping results were
obtainedby Stolarskiet al. [ 1990,Figure3] for theseyears.
In Plate 3 the increasingarea in successiveyears of the
ozonecontoursinside the vortexon day 240 indicatesthat the
ozonecolumnabundancemusthave alreadybegunto decrease
earlierin the season. The area mapping(not shownhere) of
column ozone from days 220 to 320 (early August to midNovember)showsozonedepletionevenbeforeday 220. This
is consistentwith the trends in the vortex-averagedcolumn
ozone(Plate2, Figure2a) and,asdiscussed
earlier,with recent
observations
by UARS.
Area mapping provides a convenientmeasure of the
magnitudeof maximumozonedepletioneachyear. Consider
the areaboundedby a low-ozonecontour,suchas the 250-DU
contour(Plate 3). Figure4 showsthe maximumareaenclosed
by this contourbetweendays260 and 300 (mid-September
to
late October)and the days on which the maximum area is
attainedin eachyear. Exceptin 1981 and 1986 the increaseof
the maximumarea before 1987 is roughlylinear. The linear
maximum area of the ozone hole usually occurs in late
Septemberor earlyOctober,consistent
with the vortex-average
trends discussedearlier, and also near or before the time when
the minimum ozone column amounts(not shown) are found.
One may ask whetherthis rapid growth in the chemical
ozoneholeis accompanied
(or partlydriven)by climatological
changesin the stratosphere
[e.g.,Mahlman et al., 1986, 1994;
Angell, 1993]. To addressthis questionqualitatively,we
computethe areas of the polar vortex using the -52 PVU
contourand the 195 K isotherm,both on the 500 K isentropic
surface. Figure 4 showsthese areason the same days of
maximum
area of the 250-DU
column ozone contour.
The
vortex (PV) area has little trend over the decade(only 0.05ø
yr-1;seeTable2), although
it fluctuates
interannually
abouta
more or less constant value.
In 1980 the vortex area at 500 K
is nearly twice that of the 250 DU contour,but the latter
increasesuntil it fills more than 70% of the entire vortex by
1985.
After
1985 the fluctuations
in the area of the 250-DU
contour reflect those of the vortex area itself, which limits the
size of the 250-DU
area and thus of the ozone hole.
The lack of correlationin Figure 4 between the areas
enclosedby the 195 K temperature,an indicatorof the
horizontalextentof PSCs, and the areasenclosedthe 250-DU
column ozone contour,on the days when the latter is a
maximum,is notsurprising
giventhatmuchof theprocessing
of polar air would have occurredearlier. Furthermore,
stratospheric
windscanexpose
mostof thevortexinteriorair
leastsquares
fit shows
a slopeof 8.36x 10-3 peryearfrom to PSCs, even if the latter occupiesonly part of the vortex.
1980 to 1987. The samefitting procedureshowsno trendfor
1987 - 1991 (with 1988 excluded);the averageoverthe whole
periodis 5.49 x 10-3 peryearfrom1980to 1991. Fromthe
definition
of equivalent
latitude0e,
Table2. Decadal
Growth
Rates(degree
yr-1)of
AreasBoundbyIsopleths
of 03 (250DU), PV (-52
PVU), andT (195 K)
AA(t,•*) = sin(90
ø+ 0e)A0e,
we can expressthe changein the maximum area of the 250
DU contour as an equatorwardexpansion at a rate of
approximately1.35øper yearbefore1987 andat a rate of 0.84ø
per year for the full 1980 - 1991 period (see Table 2). The
Oa
PV
T
1980-1987
1987-1991
1980-1991
1.35+0.27
-
0.00+0.28a
-
0.84+0.16
0.05+0.10
0.05+0.19
Reference
Figure4
Figure4
Figure4
aTheyear 1988is notincludedin thecalculation.
8994
JIANG ET AL.: ANTARCTIC
EQUIVALENT
-90.0
-73.7
OZONE HOLE
LATITUDE
EQUIVALENT
-66.9
-61.6
3OO
-90.0
300
LATITUDE
-75.7
'ß
-61.6
-66.9
I
"'"""
'
i
u,•,,
•,,•
._
III
Ii1./
........................................
I?....
i
I
25O
/
I
!
/
/
/
200
_1980
150
_1986
1981
1987
_1982
_1988
.....
198,5
....
1984
....
I990
.................
1985
.........
1991
.
,, ,,
lOO
2
AREA
0
i
I
4
0.04
I
1989
, ,,
•
I
0.08
0.12
AREA
Plate 4. Ozonecolumnabundanceversusareaon the daysshownin Figure4 for eachyear for 1980 - 1991.
The equivalentlatitudeis indicatedin the top axis.
This has been shown most dramaticallyfor the north [Waters
et al., 1993a], where PSCs are not so extensive. The more
critical factor may be exposureto sunlight. For short time
periodsthis exposuredependscritically on details of the air
motionwithin the vortex,but for periodsof a few weeks or
more this factor dependsmore cruciallyon the vortex extent
and locationand may be reflectedin the vortexarea shownin
Figure 4. At least to first order, most of the growth of the
ozonehole over the last decadeappearsdrivenby chemistry
alone,due to increasingstratospheric
chlorine. This increase
has slowed down, not becausethe stratosphericchlorine
loading or activation has stopped increasingbut simply
because the region of ozone-depleted air now fills
(horizontally) much of the polar vortex, whose own
fluctuationsin areareflectinterannualvariabilityin dynamical
activity.
This limiting of the ozone loss region to the vortex is
reflectedin the fact that after 1983, high contourvalues of
columnozone(largerthan300 DU) are nearthe vortexedgeas
definedhere on the 500 K isentropicsurface(Plate 3), except
in 1988. In that year the chemicallyperturbedregion was
distinctlywithin the vortex(Plate3, Figure4), as describedby
Schoeberlet al. [1989] in their analysisof the 1987 Antarctic
campaign(AAOE) data. Plate 3 and Figure4 showthat 1988
is not representative
in this regardof all otheryearsfollowing
1985. Thus further chemical ozone loss during this season
now dependsupon factorsthat would expandthe southpolar
vortex region horizontallyor which would extendthe zone of
JIANG
ET AL.: ANTARCTIC
chemicaldepletionvertically, as happenedin 1993 due to
heterogeneous chemical effects associated with the
entrainmentof Mount Pinatuboaerosolsinto the southpolar
vortex[Hofrnannet al., 1994].
Plate 4 shows the variations in ozone column abundance
versus area on the days of maximum area in the 250-DU
contour(Figure 4) eachyear from 1980 to 1991. The greater
extent of ozone-poorair in the years after 1985 is again
apparent,as is the anomalyof ozonevaluesin 1988. As more
ozonegetsdepleted,the radial gradientof ozonein the vortex
gets steeper,as can be seenfrom Figure 5, which showsthe
averagegradientof the transitionregionbetween250 DU and
280DU, definedas[280-250(DU)]/[Oe(280DU)0e(250DU)].
OZONE
HOLE
8995
days,with the changesbeingmoreprominentaway from the
vortex center. These increasesmay be due to the action of
synoptic-scale
systemswhich are known to produceminor
warmingsin the midstratosphere,
as these systemshave a
characteristic
timescaleof 10 - 20 days [e.g., Fishbein,et al.,
1993; Manney, et al., 1993a]. These dynamicaleventsaffect
ozonein the lower stratosphere
within the vortexby moving
ozone into the vortex in midstratosphere
and then down to
lower levels[e.g.,Leovyet al., 1985;Manney,et al., 1994b].
Some care needsto be taken when interpretingthe areamappedfieldsshownin Plates3 and 5, as the areamapping
tendsto filter out the planetary-scale
features. However,after
the ozonehole reachesits maximumdeptharoundday 280 in
early spring,the polarvortexstartsto shrinkand ozonecolumn
abundancestartsto recover. Significantwarmingeventsand
erosionof the vortexare markedin Plate5 by ozoneincreases
extending nearly to the vortex center. Because of the
anomalouscirculationandextremelycoldtemperature
of 1987
[Randel,1988] the final warmingandthe breakupof the ozone
hole was delayed20 days (as comparedwith climatology).
Plate 5 shows that the ozone depletionrate was never so
Years since 1984 are typically characterizedby larger
gradientsas a result of greaterozonedepletion,as discussed
earlier,with notableexceptionsin 1988 and 1989. As we have
remarkedrepeatedly,1988 is anomalousin many respects.
The relativelyweak columnozonegradientin 1989 is partly
due to the fact that the vortexarea in 1989 was the largestin
the record(Figure 4). AlthoughPlate 4 and Figure 5 show
resultsfor a singleday, the area-contours
of Plate 3 showthat persistentand as extensiveas in 1987. This decreasewas
theresultsare representative
of the ozoneholeperiodin those interruptedby a minor warming aroundday 280 and then
years. Finally,as pointedout by previousstudies[Mcintyre, terminatedby the final warmingafterday300.
1989;Hartmannet al., 1989], the steepgradientsof PV and
In 1988 on the otherhand,stratospheric
temperatures
had
ozoneindicaterelativeisolationof the chemicallyperturbed warmed significantlyby late September,terminatingmost
regionfrom air outsidethe vortex.
decreases in column ozone. The maximum total ozone decline
Plate 5 showsthe time rate of changeof ozonecolumn is only 15% duringSeptember1988 comparedto nearly50%
abundance
overa periodfromdays240 to 300 (lateAugustto duringSeptember1987 [Schoeberlet al., 1989;Kruegeret al.
late October)for eachyearfrom 1980to 1991. The resultsfor 1989]. This appearsto be the directresultof the brevityof the
1987havebeenshownpreviously
by Yunget al. [1990,Figure declinethroughSeptember. Wave activity at the time was
4]; thisfigureextendsthatresultto 12 years.The averagerate anomalously strong [Manney et al., 1991] and the
of ozonedepletionin the vortexis 1 to 2 DUd -1, consistent stratosphericsuddenwarming in late winter was reminiscent
with thatshownin Figure2b.
of major winter warmings in the northern hemisphere
Largerdepletion
rates(5 DUd -l) are prevalent
nearthe [KanzawaandKawaguchi,1990]. The 1988ozoneholebegan
centerof thevortex(Plate5). In someof therecentyears,such filling on October19, nearly six weeksearlierthan in 1987,
asthedynamically
quiescent
years1987and1989,largeozone and driftedout of the polar regionsin mid-Novemberfor the
depletionratescan persistfor long periodsof time. In most earliestbreakupsince1979.
years the development
of the ozonehole is periodically
interrupted
by increases
of ozonewith a periodabout10 - 20 5. Conclusions
The area-weighted
ozonecolumnabundance
averagedover
the polar vortexin late August (day 240), oftenviewed as the
6O
beginningof the ozonehole season,exhibitsa steadydecline
from about 320 DU in 1980 to about 250 DU at the end of the
o
N
o
40
z
o
o
z
•
20
810 ....
815
YEAR
910 '
decade. This amountsto a total drop of 70 DU in a decade
(Table 1) and accountsfor a largepart of the overalldecrease
of morethan90 DU in vortex-averaged
Octoberozonecolumn
abundance
that has occurredover the sameperiod. Most of
that drop occurredbefore 1987, as the declinesincethen has
beenmuchsmaller(Figure3).
Part of this decadal decline may be due to the recurrent
presenceof the ozonehole every year. Becauseof the long
lifetimeof ozonein the lowerstratosphere,
thereis persistence
of depletedozone from one year into the next. The effect,
known as the dilutioneffect,has beenmodeledby Sze et al.
[1989], Prather et al. [WMO, 1989, Chap. 1] andMahlman et
al. [1994]. Thesemodelspredicta declineof ozoneof 5 - 7%
at polarlatitudesin Junedue to the presenceof an ozonehole,
or about 15 - 20 DU.
That still leaves 50 - 55 DU
in the
Figure5. Averageozonecolumngradient
withrespect
to decadaldeclineunexplained.It is morelikely thattheresultis
chlorineproducingincreasing
equivalent
latitude,computed
as described
in thetext,for the due to increasingstratospheric
samedaysas in Plate4.
chemicallossof ozonein the southpolarvortexevenduring
8996
JIANG ET AL.: ANTARCTIC
•ClI'IJ. LLV1 J.N31VAII'103
3CIflILLV1 .I.N31VAIfI03
OZONE HOLE
3CIflILLV'I IN3'IVAIfI03
-8
¸
-8
.8
¸
.8
¸
r..•
o.
o
V3•1¾
V3Ei¾
V3t:lV
ß
¸
ß •,-.•
JIANG ET AL.: ANTARCTIC
southern winter, as indicated by the recent UARS
observations.
Photochemical
loss can occur because the
OZONE HOLE
8997
vortex. The dilution effect discussedabove may also play a
role. This view is necessarily speculative until more
quantitative dynamic-chemical simulations of chlorine
southernvortex is sufficientlylarge that it has regions in
sunlightevenduringthisperiodof polarnight(suchlosscould activation and ozone loss are done.
be moreheavily weightedin our methodbecauseof the areaAcknowledgments. We would like to expressour appreciationto
weightingof ourvortexaverages).
The mean ozonedepletionrate in the vortexbetweenlate R. S. Stolarskifor sharinghis insightsof the TOMS data with us. The
NMC geopotentialheightand temperaturestratospheric
analyseswere
August (day 240) and the day of minimum vortex-averaged obtainedfrom theNationalCenterfor AtmosphericResearchas part of
ozone (typically in late Septemberor early October) has an EOS interdisciplinaryscienceinvestigation;wind and PV fields
changed
fromabout1 DUd-1atthebeginning
of thedecade,were derived and providedby Gloria Manney at JPL. We thank M.
rapidly
increasing
toabout
1.8DUd-1by1985,andapparentlyAllen, L. Froidevaux,R. Herman, L. Jaegle,R. Salawitch,S. Sander,
saturatingthereafter (Figure 2b). This change in ozone and three anonymousrefereesfor valuablecomments.This work was
supportedprincipallyby NASA grant NAGW 2204 to the California
depletionratesis qualitativelybut perhapsnot quantitatively Instituteof Technologyand was carriedout there and at JPL, under
consistentwith chemicalforcingof the ozonehole solelyby contract with NASA. Contribution number 5465 from the Division of
chlorine (Figure 2c). The character and magnitude of GeologicalandPlanetarySciences,CaliforniaInstituteof Technology.
fluctuationsin the Septemberdepletionratesin 1980 - 1982
are comparableto thoseafter 1985, andit is possiblethat these References
reflectthe extratropicalQBO in ozone. A QBO signaturein
the depletionrates derivedhere is perhapsnot so strongas Anderson, J. G., W. H. Brune, and M. H. Proffitt, Ozone destruction
by chlorineradicalswithin the Antarcticvortex:The spatial and
obtainedby Lait et al. [1989] who analyzedminimumcolumn
temporal
evolution
of C10-O
3 anticorrelation
based
onin situER-2
ozoneabundanceandnot vortexaverages.The QBO signature
data,J. Geophys.Res.,94, 11,465-11,479, 1989a.
is evidentin the vortexozoneaverages
themselves
for the years
1980 - 1985 but is not readily apparentin later years. That Anderson,J. G., W. H. Brune, S. A. Lloyd, D. W. Toohey, S. P.
Sander, W. L. Starr, M. Loewenstein, and J. R. Podolske, Kinetics
interannualvariationscan affectozoneabundanceduring this
of 03 destruction
by C10andBrOwithintheAntarctic
vortex:
An
seasonis clearlyindicatedby the anomalouslyhigh column
analysisbasedon in situ ER-2 data,J. Geophys.Res., 94, 11,480ozone values during September1988, a very active year
11,520, 1989b.
dynamically.
Area mappingof variouscolumnozonecontoursprovided Anderson,J. G., D. W. Toohey,and W. H. Brune,Freeradicalswithin
the Antarctic vortex: The role of CFCs in Antarctic ozone loss,
some insight into the detailed morphologyof the ozone
Science, 251, 39-46, 1991.
depletionrate in the south polar vortex. The time rate of
changeof columnozoneappearsto be greaterdeeperin the Angell, J. K., Reexaminationof the relation between depth of the
Antarctic ozone hole, and equatorialQBO and SST, 1962-1992,
vortex (Plate 5). Whether this reflectsthe exposureof air
Geophys.Res.Lett.., 20, 1559-1562, 1993.
parcelsto sunlightor someotherfactorwas not investigated
here. Many of the regionswith the highestratesof changein Baldwin, M.P., and J. R. Holton, Climatologyof the stratospheric
polarvortexandplanetarywavebreaking,J. Atmos.Sci., 45, 1123ozoneare cold enoughthat water-icePSCs may form; if so,
1142, 1988.
greaterdehydrationand denitrificationof the vortex air may
enhancethe ozonelossthere. Regionsnear the vortexedge Bojkov, R. D., The 1979-1985 ozone decline in the Antarctic as
reflectedin groundbasedobservations,
Geophys.Res. Lett.., 13,
may have greaterdownwellingof ozone-richair during this
1236-1239, 1986.
season. The 10 to 20-day modulationof the ozone change
rates within the vortex suggeststhat synoptic activity is Bowman, K. P., Global trends in total ozone, Science, 239, 48-50,
1988.
affectingthe rate of resupply,probablyby descentof ozone
from midstratospheric
levels.
Bowman, K. P., Evolution of the total ozone field during the
Our resultssuggestthat furtherincreasesin stratospheric breakdownof the Antarcticcircumpolarvortex,J. Geophys.Res.,
95, 16,529-16,543, 1990.
chlorineafter 1985 did not significantlyincreasethe horizontal
extent of ozone loss, as the area of loss now filled most of the
Bowman,K. P., and A. J. Krueger,A globalclimatologyof total ozone
from the Nimbus7 total ozonemappingspectrometer,
J. Geophys.
inner (i.e., isolated)region of the polar vortex in the lower
Res., 90, 7967-7976, 1985.
stratosphereand was now limited by the area of the vortex.
polar
Thus depletion rates of the vortex-averageozone did not Butchart,N., and E. E. Remsberg,The areaof the stratospheric
vortexas a diagnosticfor tracer transporton an isentropicsurface,
increasefurther and in fact were not so high as in 1985 until
J. Atmos. Sci., 43, 1319-1339, 1986.
1991, when volcanicaerosolsmay have extendedthe vertical
extent of ozone chemical loss.
Chen, P., The permeabilityof the Antarcticvortexedge,J. Geophys.
Res., 99, 20,563-20,571, 1994.
In summary,our resultssuggestthat chemicalloss due to
stratospheric
chlorinewas significantevenearly in the 1980 - de Zafra, R. L., M. Jaramillo, A. Parrish, P. Solomon, B. Connor, and
J. Barrett, High concentrationsof chlorine monoxide at low
1991 period studiedhere, as judged from a vortex average.
Increasesin ozone depletionrates since 1982 are consistent
altitudes in the Antarctic spring stratosphere:diurnal variation,
Nature, 328, 408-411, 1987.
with increasingchlorineeffectsapproaching
saturationin 1985
as the region of ozonelossfilled the isolatedinner regionsof Farman,J. C., B. G. Gardiner,andJ. D. Shanklin,Largelossesof total
the polar vortex during September. In more recentyearsthe
ozonein Antarctica
revealseasonal
C1Ox/NO
x interaction,
Nature,
315, 207-210, 1985.
maineffectof increasedchlorinemay havebeento increasethe
winter time chemical loss of ozone, thereby lowering the Fishbein,E. F., L. S. Elson,L. Froidevaux,G. L. Manney,W. G. Read,
J. W. Waters, and R. W. Zurek, MLS observations
of stratospheric
thresholdon which the ozone hole developsin August and
September. This early loss would occur despite the polar
wavesin temperature
and03 duringthe 1992southern
winter,
Geophys.Res.Lett.., 20, 1255-1258, 1993.
darkness,due mainly to the great size of the southernwinter
8998
JIANG ET AL.: ANTARCTIC OZONE HOLE
Froidevaux, L., J. W. Waters, W. G. Read, L. S. Elson, D. A. Flower,
and R. F. Jarnot, Global ozone observationsfrom UARS MLS - An
overview of zonal-mean results, J. Atmos. Sci., 51, 2846-2866,
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