JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 102, NO. D7, PAGES 8945-8953, APRIL 20, 1997
The ozone hole over Punta Arenas, Chile
V. W. J. H. Kirchhoff
InstitutoNacionalde Pesquisas
Espaciais,S•ioJos6dosCampos,S•ioPaulo,Brazil
C. A. R. Casiccia S. and F. Zamorano B
Universidadde Magallanes,PuntaArenas,Chile
Abstract. Threefundamental
questions
areaddressed
for the locationof PuntaArenas(53.0øS,
70.9øW),Chile:DoestheAntarcticozoneholeextendoverthe city?If so,at whatheightis most
of the ozonedepleted?And by how muchdoesthe UVB radiationincreaseunderozonehole
conditions?
It is shownthatPuntaArenasis affectedby theAntarcticozonehole,eventhoughit is
a considerable
distanceawayfromthepole.In comparison
with the averageglobaltrendof
-0.25% peryear,the downwardozonetrendat PuntaArenasis -0.5% peryear(twiceaslargeas
the globalaverage)and-1.2% peryear(almost5 timeslargerthantheglobalaverage)usingthe
monthlyOctoberaverages.To obtainthesefigures,an ozoneclimatologyot I'OM•5 (.1otai Ozone
Mapping Spectrometer)
datafrom 1979to 1992hasbeenused.Observations
of the ozonehole
over PuntaArenasare describedduringthe australspringperiodsof 1992, 1993, and 1994.
Systematicobservations
with a Brewerspectrophotometer
havebeenmadein orderto measurethe
vertical columnof ozoneand the simultaneousvariationsin UVB radiation.In addition,the
verticaldistributionof ozonehasbeeninvestigated
duringozonehole conditions,by usingozone
ECC (Electrochemical
Concentration
Cell) sondeslaunchedon balloons,in orderto determineat
whichheightthe ozoneis reducedmost.Usingthe 220 DU (DobsonUnits)thresholdasreference,
we identifiedthe ozoneholeoverPuntaArenason five occasions
duringthe 3 yearperiodof these
observations,
September1993, October1992, 1994; andNovember 1993 and 1994. The vertical
distributionof ozoneduringozonehole conditionsshowsmaximumozonedestructionefficiency
near 15-17km, whereozonenearlyvanishescompletely,on severaloccasions.
The largestamount
of ozonedepletion,however,occursabovethis height,just underandat the main ozonepeak,
whereit may reachabout50%. The UVB radiationin smallspectralbandsmay increase
dramaticallyduringozonehole events;at 295-297 nm the observedfactorsof increasefor Punta
Arenaswere between10 and 38. The maximumintegrated/weighted
intensitiesin October,during
hole eventsincreasedover backgroundvaluesbetween2 and 3 times,which representvaluesnear
the local summermaximumbut not yet beyondlevelsnormallyobservedat low-latitudestations.
Introduction
American continent,the first with about 100,000 inhabitantsand
Ozone is an importantchemicalconstituentof the atmosphere.
One of its majorrolesin the atmosphere
is to screenout biological
damagingsolarradiationin the wavelengthregionbetween 280
and 320 nm, the UVB radiation[Brasseurand Solomon,1984]. In
addition to the global decreasingozone trend, regions near the
southpole are affectedby the Antarcticozonehole phenomenon
[Solomon, 1988, 1990]. This is a seasonalstrong ozone loss
mechanismcausedby heterogeneous
chemicalreactions[Stolarski
et al., 1986; Stolarski, 1988; Solomon and Garcia, 1986;
Andersonet al., 1991] and normallyseenin southernspring.The
NASA Total Ozone Mapping Spectrometer(TOMS) instrument
has been very importantto describeozone depletionsnear the
poles[Hermanet al., 1993].
Punta Arenas (53.0øS, 70.9øW, Chile) and Ushuaia (54.5øS,
68.0øW, Argentina) are the southernmostcities of the South
Copyright1997 by the AmericanGeophysicalUnion.
Papernumber96JD03609•
0148-0227/97/96JD-03609509.00
the secondwith about30,000. Thesepopulationsare the first
groupof peoplethathavebeenexposedto the ozoneholeeffects,
includinglargerintensitiesof UVB radiation.To studythese
effectson a long-termbasis,andto producelocalcompetence
in
this scientificarea,a Brewerspectrophotometer
was installedin
Punta Arenas's University of Magallanesin June 1992, in
collaboration
with the InstitutoNacionalde Pesquisas
Espaciais
(INPE) of Brazil [Kirchhoffetal., 1993].
Instrumentation
Total
ozone as well
as UVB
radiation are measured
systematically
with a Brewerspectrophotometer
[Brewer,1973;
Brewerand Kerr, 1973]. This instrument
was developedby the
Canadian Atmospheric Environment Service and has been
commercially
availablesincethe early 1980s.Presently,
thereare
more than 100 of these instrumentsin operation.It was
specificallydesignedto meetthe very demanding
performance
criteriato measure
accurately
the ultravioletradiationnecessary
for the calculation
of ozonecolumnamountsusingdirectsolar
beam absorption.The Brewer instrumentmakes spectral
8945
8946
KIRCHHOFF
ET AL.' OZONE HOLE OVER PUNTA ARENAS
Results
observationsat wavelengthsbetween 290 and 325 nm. The
and Discussion
resolution for ozone observations is about 0.6 nm, and the
wavelengthsare placedat 306.3, 310.0, 313.4, 316.7, and 319.9 Ozone AveragesOver Punta Arenas
nm. The instrumentincludes automaticwavelengthcalibration
The Antarcticozone hole is clearly a polar phenomenon,in
using an internalmercurydischargelamp, as well as a relative
spectralintensitysourcefrom a quartz-halogen
lamp.A computer- which the polar vortex and its dynamicsand the extremelylow
stratospherictemperaturesplay importantroles [Schoeberland
controlledazimuthmountensuresautomaticsolarpointing.
Hartmann, 1991]. However,whenthe polarvortexbreaksup and
The vertical distribution of ozone over Punta Arenas has been
determinedby usingozoneElectrochemical
Concentration
Cell the ozonehole startsto disappear,largevolumesof low-ozoneair,
to
(ECC) sondeslaunched
on balloons.The balloonsonde
is a small whicharepiecesof the disruptedpolarair, may be transported
lower
latitudes,
where
they
act
as
local
perturbations.
Such
20x30x30 cm instrumentdevelopedin the early 1970s[Komhyr,
1969; Komhyrand Harris, 1971], which flies togetherwith a perturbationshave been reportedfrom observationsat lower
standard radiosonde, providing, in addition to ozone latitudes[Atkinsonet al., 1989; Kane, 1991; Thompson,1991;
concentrations,
temperature,humidity,and pressure.The ozone Kirchhoffet al., 1996b]. Model calculationshave also predicted
to lower latitudes,
sensoris basedontwo platinumelectrodes
immersed
in a liquidin thatAntarcticozonelows may be transported
asshownby PratherandJaffe[1990] andPratheret al. [1990].
which a chemical reaction occurs when ozone is introduced into
PuntaArenasis not within the Antarcticcircle.Clearly, Punta
the chemicalsolution.The resultof the reactionis the production
of free electrons,which are amplified to an electric current Arenasis not alwaysinsideof the Antarcticozonehole region.
proportionalto the ozone concentration
bubbled into the Doesthatmeanthat it is not affectedby the Antarcticozonehole?
electrodesfrom the outsideair. The digital ozonesondes
usedcan In orderto answerthis questiona NASA database,that includes
makeasmanyas 60 ozoneobservations
perkilometer,including 14 yearsof TOMS (version6.0 [Kruegeret a/.,1992]) data,was
pressure,
temperature,
humidity,temperature
of thesensor,
battery used.An ozoneclimatologyfor PuntaArenaswas obtainedfrom
that is usedin this work for
voltage,andozone.Thistechnique
hasbeenusedextensively
over this 1979to 1992 dataset,a sequence
basic
comparisons.
In
what
follows
it
will be designated
as the
thelast10yearsfor ozoneobservations
[Kirchhoffet
al., 1991].
referencehistoricalclimatology(RHC). On the basis of these
background
datawe showthatthereis an obviousand systematic
Objective
effect of the Antarctic ozone hole over Punta Arenas.
The objectiveof this work is to describethe appearance
of the
ozone hole over Punta Arenas, Chile, during the years 1992,
1993, and 1994, using observations of a Brewer
spectrophotometer
installed specifically for this purpose. In
addition, the vertical distributionof ozone during ozone hole
conditionswasmeasured
usingozoneECC sondes.The intensities
of the UVB radiation during ozone hole conditionsat Punta
Arenas are comparedwith normal low-latitudeUVB radiation
at Natal, Brazil (6øS).
Figure 1 showsozonecolumnamountsin DobsonUnits (DU)
as a functionof time in years.The yearly averagecolumnozone
amountsfrom the above mentionedclimatologyare shown in
Figure 1 by squares.Theseshowa clear downwardtrend of the
ozone columnamounts.A simple linear fit to the data gives a
trendof-0.5% per year, twice as large as the global average
trend [World MeteorologicalOrganization, 1988, 1989] of
-0.25% per year. Becauseof the ozone depletionsin springthe
total ozonecolumnamountsdecreasesignificantlywith respectto
the yearly averages;this decreaseis shown in Figure 1 by the
375
_
350 --
325 --
300 ::::3
--'
_
275-
ILl
Z
0
_
250--
N
0
-
225-_
200 _
175_
150
I
1978
'
I
1980
•
I
1982
'
I
1984
'
I
1986
'
I
1988
'
I
1990
'
I
1992
YEAR
Figure 1. Ozone climatologyfor Punta Arenas (53.0øS, 70.9øW), Chile, obtainedfrom Meteor 3/TOMS
(version6) data. Shownare the yearly averages,(squares)and a linearfit of-0.5% per year. Also shownare
yearlyminima(asterisks)andOctoberminima(triangles).
KIRCHHOFF ET AL.: OZONE HOLE OVER PUNTA ARENAS
,
45O
I
,
I
'
I
,
I
'
I
,
I
,
I
'
I
'
I
,
I
'
I
,
I
'
8947
I
--
420 _
390 _
360 --
330 _
300 _
270 _
240 _
210
'
1978
1980
1982
1984
1986
YEAR
1988
1990
I
1992
Figure 2. Ozoneclimatologyfor PuntaArenas,Chile obtainedfrom Meteor3/TOMS (version6) data.The
Octoberaverages
areshown.A simplelinearfit for trendanalysisgives-1.2% peryear.
yearly minima(asterisks);
at PuntaArenastheseyearly minima Brewer SpectrophotometerObservations
may occurin September,October,or November.Figure 1 also
shows the October minima (triangles). Roughly, the yearly
In additionto UVB radiation,we obtainedsystematicozone
minimum from 1978 to 1988 was near 250 DU, but from 1988
columnamountsusing a Brewer spectrophotometer
in Punta
onward,the minimum is decreasingat a considerablyfasterrate;
the 1992 minimum was 164 DU, and it was 196 DU the year
Arenas. For the 3 years of observations,ozone column values
were extremelylow on severaloccasions.For this study, low-
before. The Brewer data show a minimum ozone column for 1994
ozone events were defined as those below 2 standard deviations of
of 145 DU in October(for which the climatologicalaverageis
334 DU). This appearsto have beenthe lowestozonecolumn
observationever for Punta Arenas.During the last 4 years the
yearlyminimaall occurredin October.
Figure2 showsaverageozonecolumnamountsfor the month
of October,as a function of time in years, using the monthly
October means of the above mentionedozone climatology for
PuntaArenas.The rateof ozonedecrease
givesa linearfit trendof
-1.2% per year, 5 times the global averagetrend. It is clear
therefore that Punta Arenas is considerablyaffected by the
Antarcticozonehole phenomenon.
From observations
of satelliteimagesof total ozonein the area
of interestit is clearthatthe transporttime constantfor changeis
of the order of only a few days, whereasthe chemicaltime
constantfor ozoneis muchlarger[Anderson
et al., 1991;Molina
et al., 1987].The ozoneholeitselfis definedin thisstudyby the
the climatologicalmean; thesevalues are listed in Table 1. We
observedozone hole conditionson five occasions,using the
criteria that the observer is inside the ozone hole when the ozone
column decreases below 220 DU.
Table
1 with
These events are shown in
an asterisk. The ozone decreases in terms of
percentage,
shownin Table 1, are calculatedby usingasreference
the RHC defined earlier (monthly averages are shown in
parentheses
in column3 of Table 1).
The five ozone hole events (shown in Table 1 with an
asterisk*)observedat PuntaArenasduring1992, 1993, and 1994
are further describedin Table 2; all days with column ozone
values less than 220 DU are shown. The event number of the
secondcolumnis the samenumberusedin Table 1. Again, the
percentreductionis determinedby using the RHC as reference.
Threeof the ozonehole eventslastedonly 1 day;that is, although
the ozone may have been low on the days before and after the
geographic
areainsideof whichthe ozonecolumnhaslessthan event, it was higher than 220 DU. These were all ozone hole
220 DU. This is normallya roundedlarge area over the south eventsthat occurredin either Septemberor November. During
pole.Theexactshapeis notalwayscircular;it maystretchoutin Octoberthe ozone hole eYentsat Punta Arenas were longer: 3
an ellipticalshape,for example[Hermanet al., 1995a,b]. When days in October 1992 and 7 days in October 1994. The largest
this featuretakes an oval shape,it may sweepover the Punta ozone reduction was observedon October 17, 1994, when a 60%
Arenasarea.Examinationof manyof theseoccasions
showsthat reduction(morethanhalf the layer)occurred.
the ozoneholeoccursoverthe city whenthe Antarcticozonehole
Daily average ozone column observationsmade with the
reachesout in an elongatedshape;duringtheseoccasions
the tip Brewer spectrophotometer
are shownin Figures3-5. The shaded
of theozoneholemaystayoverPuntaArenasfor a few days,after rectanglein eachpanel,introducedas a backgroundin the figures,
whichthe elongatedshapeof the hole stretches
back,becoming is the averageplus or minus 1 standarddeviationfrom the ozone
circularagain,or the oval shapecontinues
but rotatesbeyond climatology described earlier (the RHC). Figure 3 is for
PuntaArenas, eitherto the west or to the east.
September,Figure4 is for Octoberand Figure 5 is for November.
8948
KIRCHHOFF
ET AL.: OZONE
HOLE OVER PUNTA
ARENAS
Table 1. Low-OzoneEventsObservedat PuntaArenasDuring 1992,1993,and 1994
Date of Minimum
Ozone
Event
Ozone Low,
DU
Ozone
Decrease,
Duration,
(%)
Days
3
1
2
3
4
5
6
Sept.05, 1992
Sept.24, 1992
Sept.10, 1993
Sept.27, 1993
Sept.08, 1994
Sept.15, 1994
241.2 (330)
245.0 (330)
264.1 (330)
205.9 (330)*
263.0 (330)
237.8 (330)
26.9
25.7
20.0
37.6
20.3
27.9
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Oct. 05, 1992
Oct. 04, 1993
Oct. 15, 1993
Oct. 22, 1993
Oct. 26, 1993
Oct. 02, 1994
Oct. 10, 1994
Oct. 17, 1994
Nov. 01, 1993
Nov. 12, 1993
Nov. 28, 1993
Nov. 04, 1994
Nov. 10, 1994
Nov. 18, 1994
Dec. 08, 1992
190.3 (334)*
235.1 (334)
238.6 (334)
236.1 (334)
230.9 (334)
261.9 (334)
235.3 (334)
145.8 (334)*
251.0 (334)
219.3 (334)*
266.0 (334)
244.1 (334)
204.6 (334)*
238.4 (334)
266.4 (334)
43.0
29.6
28.6
29.3
30.8
21.6
29.5
56.3
24.8
34.3
20.3
26.9
38.7
28.6
20.2
2
1
4
1
2
4
2
2
3
3
1
4
7
4
7
2
3
8
6
3
*Events further described in Table 2.
In addition,the figuresshowa line at 220 DU, for reference;
this Figure4. Two largehole eventsare seenfor 1992 and 1994, when
is the threshold value we have chosen to define the ozone hole
the ozonewent below 220 DU. A largehole eventwas seenon
condition,as mentionedbefore.Figures3 to 5 showthat thereis October5, 1992, when the daily averagewas 190.3 DU. The
considerable
ozonevariabilityin a monthlytime interval.This is lowerlimit wasreachedat a downwardrateof 31.25 DU per day,
mainly causedby transportof ozoneirregularitiesover the Punta startingaroundOctober1. PuntaArenaswas clearlyinsidethe
Arenas instrument,as mentionedalready.The vertical error bars
in Figures3 and 4 showthe typicalsizeof the standarddeviation
of the daily mean,asobservedby theBrewerspectrophotometer.
Figure3 showsthat low ozonevaluesare seenin Septemberof
all years,but there is only one occasion,in September1993, on
ozone hole area on October 4, 5 and 6, as shown in Table 2. After
this date the elongatedozone hole pattern shifted eastward,
beyondthe city limits of Punta Arenas, and the ozone levels
started to increase.
During October 1993 the lower limit of 220 DU was never
reached,but in 1994 again the ozone hole was presentfrom
which the ozone becomeslarger than the climatologicalmeans October 14 to 19. The lowestvalue seenduring this period was
usedfor comparison,but clearly,for mostof the time the ozone 145.8 DU, on October 17. This lower limit ozone column value
valuesare below average.Similar resultsare seenfor October,in represents
only 43% of the climatologicalmean(RHC), and was
which the threshold of 220 DU is reached. There are occasions on
Table 2. DaysWith OzoneHole Conditions(03 Lessthan220 DU) at PuntaArenas;
During 1992, 1993, and 1994
Ozone
Sequence
Event
Dates Of
#
Event
Ozone,
DU
Decrease,
%
1
04
Sept.27, 1993
205.9
37.6
2
07
07
07
14
14
14
14
14
14
14
16
19
Oct. 04, 1992
Oct. 05, 1992
Oct. 06, 1992
Oct. 13, 1994
Oct. 14, 1994
Oct. 15, 1994
Oct. 16, 1994
Oct. 17, 1994
Oct. 18, 1994
Oct. 19, 1994
Nov. 12, 1993
Nov. 10, 1994
202.8
190.3
203.5
250.7
216.1
195.6
192.2
145.8
193.9
197.2
219.3
204.6
39.3
43.0
39.1
24.9
35.3
41.4
42.4
56.3
41.9
40.9
34.3
38.7
3
4
5
KIRCHHOFF
ET AL.' OZONE HOLE OVER PUNTA ARENAS
was held during October 1995 in Punta Arenas. This special
campaignwill be describedelsewhere.
Figure 6 shows ozone concentrations(in partial pressureof
ozone,nanobars)as a functionof height.Two ozoneprofiles are
400 -
--•
360-
I•
-
m
320-
•'•
_
"7
shown, one for an ozone hole condition and the other for
• • 3•
ß14.8
DU
280-
O
240 -
•0
_
comparison.
The comparison
profileis a "typical"ozoneprofile at
the latitudesof interest.Obtainedin a seasonalperiod when the
ozoneholehadcompletelydissipated(January21, 1991), it shows
peak ozone concentration
near 40-50 hPa, which corresponds
to
19-21 km. The tropopause
transitionis near 8-10 km. In contrast,
DU
400 .
---
360-
I•
thesecond
profileshown
in Figure6 wasobtained
in themiddie
-
•
320-
•J•
_
"7
280-
O
240 -
220 DU
400 -
•',
360-
•
320-
•
280 -
8949
330 +14.8
•/•Y////•///•
DU
•//////////•/////////////////////////F///•F/•///////////•
0
240 -
220 DU
200
'
I
0
'
5
I
'
10
I
'
I
'
15
20
SEPTEMBER
I
'
25
I
'
of the ozonehole period of 1992, on September25. As can be
seen,this profile representsa severeozonehole conditionfor the
Ferrazstation.The hatchedareabetweenboth profilesis equalto
the ozone lossbetweenthe normal and the perturbedcondition.
Ozonelossesoccurredin the lower stratosphere
at all heights,but
the largestpercentageof loss occursat 15-17 km, where ozone
destructionis almostcomplete.Higher up, near the peak of the
ozonelayer, the depletionis closeto 50%, and mostof the ozone
lossin terms of the layer contentcomesfrom this height region,
that is, 18-25 km. It is interestingto note that the ozonehole did
not reach as far as Punta Arenasthis day. However, more recent
soundingeventsat Ferraz, at PuntaArenas,and at Siowa station
confirm the general descriptionof the vertical distribution of
ozoneduringhole condition,asdescribedin Figure 6.
30
Figure3. Brewerspectrophotometer
September
dailyaverages
for
1992, 1993, and 1994 for PuntaArenas.The hatchedrectangle
represents
the climatological
averageplusandminusthe standard
deviation,shownfor reference.Vertical barsare typical standard
deviationsfor the daily means.The 220 DU thresholdline is
shownfor reference.A hole conditionwas observedon September
27, 1993 (daily averagewaslowerthan220 DU).
•,
360-
•'•/////////7'////////,•////////////7//•/•///••////////////////•//•1
e-,,
320-
•//////////////////////•//////////////////////////////•/•/////////,•////////////////////,•
•
280--
½
240-
•0
200
I
,
160---
reachedat a rate of 21.1 DU per day, startingOctober8, as shown
in Figure4.
The ozone hole condition
over Punta Arenas can be seen as far
into summeras November, as shown in Figure 5. In contrastto
1992, which had ozone values very close to the climatological
mean, both 1993 and 1994 had at leastone occasionof very low
ozone: 219.3 DU for November 12, 1993, and 204.6 DU for
November 10, 1994. In addition,duringthe whole month, values
in 1993 and 1994 stayedconsiderablybelow the climatological
I
400 --
I
334 +-28 DU
360---
320-280---
240-_
200 -
220 DU
160-_
I
400 -
I
I
334 -+ 28 DI,
_
mean.
The ozone hole condition
was not observed
in the data for
December. However, there is a clear decreasein ozone values in
Decemberin comparison
with the climatologicalaverages.
Ozonesonde
Measurements'
Vertical
Distribution
360-
/
_
280 -240--
of Ozone
/
320 --
-
200 --
220 DU
160-_
Measurements
distribution
were
made
of the ozone column do not show the vertical
of ozone concentrations.
to
obtain
the
Ozonesonde
vertical
measurements
distribution
of
ozone
concentrationduring normal and perturbed conditions. The
soundingswere made acrossthe Magallanes channel at King
GeorgeIsland,the BrazilianAntarcticStationComandanteFerraz
(62.1øS,58.4øW). Severalsondeswere launchedduring summer
1991, and the whole winter/spring1992 period. The data have
been describedby Kirchhoffand Marinho [1992] with emphasis
on the troposphere
and by Kirchhoffet al., [1996a] with emphasis
on the stratosphere.
Another specialozone soundingcampaign
15
OCTOBER
20
25
3o
Figure 4. Brewer spectrophotometer
Octoberdaily averagesfor
1992, 1993, and 1994, for PuntaArenas.The hatchedrectangle
represents
the climatologicalaverageplus and minus 1 standard
deviation,shownfor reference.Vertical barsare typical standard
deviationsfor the daily means.The 220 DU thresholdline is
shown for reference. A hole condition was observed around
October5, 1992; and October17, 1994 (daily averagewas lower
than 220 DU).
8950
KIRCHHOFF
ET AL.: OZONE HOLE OVER PUNTA ARENAS
- (•
334
+15
DU
360•
330-
, I , I , I [ I , I , I , I , I •
25
390 -
3
SEPTEMBE
300-
20--
270
240 -
4
22o
9u
39O
360
33O
I
I
I
I
I
334 • 15 DL
3oo
270
240•-
I
39O
I
I
I
9u
I
I
-
3e,
344 •15 DU
4
5--
FERRAZ
1992
5
300-
6
7
270
240
0--
DU
210
'
I
'
15
I
2O
'
I
25
"
0
I
20
40
60
80
100
OZONE
3O
120
140
160
180
(rib)
NOVEMBER
Figure 6. Vertical distributionof ozone near Punta Arenas for
Figure 5. Brewerspectrophotometer
Novemberdaily averages
for normal and perturbed(ozone hole) conditions,obtainedfrom
1992, 1993, and 1994, for Punta Arenas. The hatchedrectangle ozonesoundings.
The normal layer, shown for reference,was
represents
the climatologicalaverageplusandminusthe standard obtainedon January21, 1991. The perturbedozoneprofile was
deviation, shown for reference.The 220 DU threshold line is obtainedon September25, 1992.
shown for reference. A hole condition was observed on November
12, 1993, and November 10, 1994 (daily averagewas lower than
220 DU).
,
25
I
,
I
,
I
,
I
,
I
,,I
i
I
,
I
•
-3
The ozone profile with the strongestozone loss, closest(in
timing) to the ozonehole eventsobservedin PuntaArenasduring
1992, is shownin Figure7. This is for October3, 1992, 1 day
OCTOBER
O3
-4
1992
-5
before the ozone hole condition observed at Punta Arenas,
October4, 5, and 6, 1992. The strongsurfacewinds commonon
the islandsof the AntarcticPeninsula,resultin very long ranges
betweenthe balloonand the groundantenna.In somecasesthey
causethe lossof signalbeforeballoonburst.This makessomeof
the profiles incomplete,as in this case for October 3, 1992.
Ranges of 100-150 km distancehave been obtained when the
balloon is at heights of 18-20 km. On October 3 the Brewer
spectrophotometer
at Punta Arenasmeasuredan averageof 267
DU, well below the climatologicalaveragebut still abovethe 220
DU hole threshold.Again, in Figure7 the controllayer usedfor
comparisonis that for January21, 1991. The October3 sounding,
althoughincomplete,clearly showsthat againthe percentageof
m10•E
_
-3
_
_
-4
5--
--
ozone destruction was most severe near 15-16 km, where the
--
ozone concentration virtually vanished (from a normal
concentration
of about80 nbar). Up to about19 km, just below
the ozonepeak, the ozoneconcentrationis reducedby more than
60%, whichis probablymaintainedupward.As mentioned,ozone
soundingsmade in Punta Arenas during October 1995 have also
20
40
60
80
OZONE
100120140160180
(nb)
shown this behavior of severe ozone destructionnear 15 km, as
Figure 7. Vertical distributionof ozone near Punta Arenas for
observed,for example,in the soundingsof October11,12, and 13,
1995 (not shown). In summary, during ozone hole conditions,
vertical soundingsshowthat there is severeozonereductionin the
lower stratosphere.On many occasionsthe ozone concentration
normal and perturbed(ozone hole) conditions,obtainedfrom
ozonesoundings.
The normal layer, shown for reference,was
obtainedon January21, 1991. The perturbedozoneprofile was
obtained on October 3, 1992.
KIRCHHOFF
1 E+0
ET AL.' OZONE HOLE OVER PUNTA ARENAS
-
8951
- 1 E+3
_
_
1E+2
1E+1
•-- 1E+0
_
_
--1E-1
_
_
_
_
_
i
1 E-5
1E-2
IIIlllllllllllllllllllllllllllllll
29O
295
300
305
310
315
320
3:25
WAVELENGTH(rim)
Figure 8. SpectralUVB intensitymeasurements
as a functionof wavelength.Two spectraare shown,one on
October 4, 1992, for low (triangles) and one on October 12, 1992, for normal (diamonds) ozone column
amounts.Also shown(circles)is the ratio betweenthe two spectra,showingmaximumenhancements
at 295297 nm.
nearly vanishesat heightsof 15-17 km. Near the peak of the
ozonelayerthe ozonelossmay decreaseto 40-60%.
UVB
high columnozone, is a strongfunctionof wavelength,with a
peakbetween295 nm and297 nm (the verticaldot-dashed
line at
295 nm is shownfor referenceonly). This peak may be an
unexpected
result,an artifactresultingfromstraylightphenomena
at the very low wavelength,where the instrumentalcorrections
Measurements
As we mentionedbefore,the Brewerspectrophotometer
makes
UVB measurementsbetween290 and 325 nm. Figure 8 shows become marginal. The instrumental behavior in this shortUVB spectraobtainedat PuntaArenas,that is, the UVB spectral wavelength
regionis presentlyunderfurtherinvestigation.
In any
intensity
in W/m2/nm
asa function
of wavelength,
from290to
casethe maximumvalueof the ratio,near296 nm, is quitelarge,
325 nm. Theseare true intensitymeasurements;
that is, they have
not yet beenweightedby spectralbiologicalsensitivityfunctions.
The spectralUVB intensitiesshownin Figure 8 are for 2 days in
1992: October 4, when ozone was reduced (triangles), and
referenceonly). The ratio decreasesfor longer wavelengths,
becomingnearlyunity at 325 nm, whereozoneis no longeran
nearly 22 (the horizontal dot-dashedline is shown at 22 for
importantabsorberof UV radiation.
October 12, when the ozone at Punta Arenas was normal
(diamonds).Figure 8 also shows a curve for the ratio of both
The UV spectraobtainedfrom the Brewerwereweightedby
the InternationalIlluminationCommission
(CIE) [1987] action
spectrafor erythema,which give a general indication of the
spectra,provingthat the spectralintensityvariation,from low to
4•0
•JIIJIIIIIIIIIIIIIIIJIIIJIIIIIIIi3500
400
.
- -.•
• 3000
r'•7r'• I•11:
360
2500
.O. 320
2000
O 280-•
1500
r-
N
o
240
lOOO
.
200
160
0
4
8
12
16
OCTOBER
20
24
28
32
1992
Figure 9. Brewer spectrophotometerozone column amounts for October 1992 at Punta Arenas and
simultaneous
UVB radiationintegrated/weighted
daily integrals,showingexpectedstronganticorrelation,
for
daysof low ozone.
8952
KIRCHHOFF ET AL.: OZONE HOLE OVER PUNTA ARENAS
400
-
•350
NATAL
300-
•250200
4AND
6OCT.
1992
150
-
lOO
200
220
240
260
280
300
JULIAN
320
340
360
380
DAY
Figure 10. Comparison
of daily maximaUVB integrated/weighted
intensities
for PuntaArenas(53.0øS,
70.9øW),Chile,andfor Natal (6.0øS,35.0øW),Brazil.
biological importanceof the UV radiation. The weighted theseincreases
may represent
muchmorethanwe canevaluateon
irradiances
were then integratedover wavelength,and over each thebasisof ourcomparison
with only low-latitudevalues.This is
day, givingthe integratedUVB intensities.
an interesting
question
thatmustbe investigated
further.
Increasesof UVB radiationduringlow-ozoneevents(that is,
the expectedanticorrelations)
are shown for October 1992 in Conclusions
Figure 9. Here the UVB radiationis weightedby the erythema
actionspectrum[CIE, 1987]. Shownarethe ozonecolumnvalues,
We investigated
ozonehole conditionsfor the city of Punta
already described,and the UVB radiation (CIE-weighted) Arenas,Chile.From a NASA ozonedatabase,
from 1978to 1992,
integrated
for eachday(J/m2).As expected,
thereis a clear
we determined that the downward ozone trend at Punta Arenas is
negativecorrelation,with high UVB doseson occasionsof low
twiceaslargeastheglobalaverage
whentheyearlyaverages
are
ozone. The casefor October4 is evident, when the UVB radiation usedand 5 timesas largewhenthe Octoberaverages
are used.
dosesincreasedover their backgroundvaluesfrom about1000 to This finding clearly showsa stronginfluenceof the Antarctic
3000J/m
2, anincrease
ofa factor
of 3;thisisstilla largefactor ozone hole conditionon the city of Punta Arenas. Local
but much lessthan the spectralmaximumof 22, shownin the measurements
were obtainedwith a Brewerspectrophotometer
previousfigure. For October4 and 6 the UVB intensitiesalmost
equal the summermaxima at Punta Arenas. For October20 the
integratedUVB increaseis alsolarge,abouta factorof 2.
To determinehow the PuntaArenasradiationcompareswith
normal low,latitude observations,where the largest UVB
radiationsare expected,the PuntaArenasdaily UVB maximaare
comparedwith UVB valuesmeasuredat the low-latitudestation
Natal (6øS,35øW),Brazil; only databetweenthe middleand end
of Octoberare availablefor Natal, as shownin Figure 10. The
observations
of
Natal
were
also obtained
with
a Brewer
from 1992 to 1994; we examinedthe ozone hole conditionand
foundthatthethreshold
of 220 DU waspassed
onfive occasions.
The longest-duration
hole conditionover PuntaArenasoccurred
in October1994 (7 days),whenthe ozonecolumndecreased
to
145 DU, a dramatic reductionto less than half the ozone column
thickness.The UVB radiationduring ozone hole conditions
increased
l>ya factorof 22 at the wavelength
of 295-297nm.
Whenintegrated
between
290and325nm,andweighted
by the
CIE erythemaactionspectrum,the UVB radiationfor the 1992
hole event,for example,increased
on October4 and 6 to values
spectrophotometer,
the sametype of instrumentas was used at observed
normallyin the summer.
However,theseexceptional
Punta Arenas. The comparisonclearly showsthat the radiation ozonehole, large UVB increasesobservedat PuntaArenasare
spectraobservedunderspecialozonehole circumstances
at Punta still below the normallimits of low-latitudemeasurements,
as
Arenas,Chile, are still lower (by roughlya factor of 3; around shownin comparison
with observations
at Natal.
0.18at PuntaArenas
andaround
0.35W/m2, CIE weighted,
at
Natal) than normal UVB radiation levels observedfor the Natal
station.
It is interestingto speculateaboutthe UVB increases
that were
observed:what do they actuallymeanbiologically?Clearly,for
"normal"conditionsit wouldappearthat absolutevalueshavenot
yet reachedalarminglevels,for example,thosemuchhigherthan
normalequatorialreadings.On the otherhand,localliving beings
may have adaptedto normally low Antarctic UVB levels, and
Acknowledgments.
It is a pleasureto acknowledgevaluable
supportof Victor Valderrama,RolandoAguilar,andthe staffof
the Universityof Magallanes
andof INPE (INPE is partof the
MCT, the Ministryof Scienceand Technology).The work at
PuntaArenasby the Grupode EstudiosAtmosfericos
is a natural
extension
of activitiesinitiatedby the INPE OzoneGroupat the
BrazilianAntarcticstationComandante
Ferraz,on King George
Island,near the Antarctic Peninsula.We are gratefulto the
KIRCHHOFF
ET AL.' OZONE HOLE OVER PUNTA ARENAS
BrazilianPROANTAR program,of CNPq (the BrazilianNational
ResearchCouncil), for financial support.Logistic supportwas
providedby the Brazilian Air Force and the Brazilian Navy.
Researchgrantsfrom CNPq, FAPESP (Fundagio de Amparo h
Pesquisado Estadode Silo Paulo), and FINEP (Financiadorade
Estudose Projetos)areacknowledged.
8953
Komhyr, W.D., Electrochemicalconcentrationcell for gas
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Krueger, A.J., L.M. Penn, C.J. Scott, and D.E. Larko, Nimbus 7
total ozone mapping spectrometer(TOMS) Antarctic ozone
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(ReceivedApril 20, 1996;revisedOctober28, 1996;
acceptedOctober28, 1996)