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3TheEffectofRepresentingBrominefromVSLSonthe4
SimulationandEvolutionofAntarcticOzone567
LukeD.Oman1,AnneR.Douglass1,RossJ.Salawitch2,8TimothyP.Canty2,JeraldR.Ziemke1,3,andMichaelManyin1,49
1011
1NASAGoddardSpaceFlightCenter,Greenbelt,MD,USA122UniversityofMaryland,CollegePark,MD,USA133MorganStateUniversity,Baltimore,MD,USA14
4ScienceSystemsandApplications,Inc.,Lanham,MD,USA15161718
SubmittedtoGeophysicalResearchLetters19202122232425Keypoints:26271.Including5pptofBrfromVSLSreducesbiaseswithobservedozoneandBrO28292.Resolvesadiscrepancywithanobservationalderivedparametricmodel30313.CausesadecadelaterrecoveryofAntarcticozoneto1980levels32333435CorrespondingAuthor:36LukeD.Oman37NASAGoddardSpaceFlightCenter38AtmosphericChemistryandDynamicsLaboratory39Code61440Greenbelt,MD2077141E‐mail:[email protected] 43
https://ntrs.nasa.gov/search.jsp?R=20170002555 2020-04-04T11:18:28+00:00Z
2
Abstract44
WeusetheGoddardEarthObservingSystemChemistry‐ClimateModel45
(GEOSCCM),acontributortoboththe2010and2014WMOOzoneAssessment46
Reports,toshowthatinclusionof5partspertrillion(ppt)ofstratosphericbromine47
(Bry)fromveryshort‐livedsubstances(VSLS)isresponsibleforaboutadecade48
delayinozoneholerecovery.Theseresultspartiallyexplainthesignificantlylater49
recoveryofAntarcticozonenotedinthe2014report,asbrominefromVSLSwasnot50
includedinthe2010Assessment.Weshowmultiplelinesofevidencethat51
simulationsthataccountforVSLSBryareinbetteragreementwithbothtotal52
columnBrOandtheseasonalevolutionofAntarcticozonereportedbytheOzone53
MonitoringInstrument(OMI)onNASA’sAurasatellite.Inaddition,thenearzero54
ozonelevelsobservedinthedeepAntarcticlowerstratosphericpolarvortexare55
onlyreproducedinasimulationthatincludesthisBrysourcefromVSLS.56
1.Introduction57
Simulationsofthefutureevolutionoftheozonelayershowthatthetime58
frameofozonerecoverydependsonthehalogenandgreenhousegas(GHG)59
emissionsscenariosandforecastchangesinthetemperatureandcirculationofthe60
stratosphere,eachwithvaryingimportancedependentonlatitudeandseason61
[Eyringetal.,2013a;Omanetal.,2014;WorldMeteorologicalOrganization(WMO),62
2014].Bromineplaysanintegralpartindeterminingtheatmosphericabundanceof63
ozoneanditseffectivenesspermoleculeatdestroyingozoneisapproximately45‐6564
timesgreaterthanchlorine[Danieletal.,1999;Sinnhuberetal.,2009].Inaddition,65
thebromineimpactonozonedepletionislargerwithhigherchlorine[McElroyetal.,66
3
1986]aswellaswithenhancedsulfateaerosolloading,likefollowinglargevolcanic67
eruptions[Salawitchetal.,2005].68
Brominefromveryshort‐livedsubstances(VSLS),mainlybromoform69
(CHBr3)anddibromomethane(CH2Br2)hasalsobeenshowntobeanimportant70
partofthetotalatmosphericburdenofbromineandozonelayerchemistry[Koet71
al.,1997;Sturgesetal.,2000;Salawitchetal.,2005].Theysetal.[2007]estimated72
thatVSLSsupply6to8partspertrillion(ppt)ofstratosphericBrybasedon73
retrievalofstratosphericandtroposphericcolumnBrOatReunion‐Island(20.9°S).74
Salawitchetal.[2010],focusingontheArctic,foundthat5to10pptofstratospheric75
brominefromVSLSisneededtoachieveconsistencywithaircraftandsatellite76
measurementsofBrO.Liangetal.[2014]quantifiedthechemicalandphysical77
transformationsofVSLSafterreleaseintothemarineboundarylayerusingthe78
GoddardEarthObservingSystemChemistry‐ClimateModel(GEOSCCM)and79
concludedVSLSsupplyabout8pptofbrominetothebaseofthetropical80
tropopauselayer.MeasurementsofupperstratosphericBrOfromtheMicrowave81
LimbSounder(MLS),balloon‐borneDOAS(DifferentialOpticalAbsorption82
Spectroscopy),andtheScanningImagingAbsorptionSpectrometerforAtmospheric83
Chartography(SCIAMACHY)yieldestimatesforVSLSsupplyofstratosphericBryof84
5±4.5ppt[Millanetal.,2012],5.2±2.5ppt[Dorfetal.,2008],and7±6ppt85
[Parrellaetal.,2013],respectively.86
Afewstudiesexaminedtheimpactofthisadditionalbromineon87
stratosphericozoneconcentrations.Frieleretal.[2006]showedinclusionof88
brominefromVSLSledtobetteragreementbetweenobservedandmodeledlossof89
4
Arcticozoneforaparticularwinter.Fengetal.[2007],focusingonmidlatitude90
ozone,founda10DUdecreasebyincluding5pptofbrominefromVSLS.Yangetal.91
[2014]madearoughestimateof6‐8yearslaterrecoveryoftheAntarcticozonehole92
dueto5pptofbrominefromVSLSbasedontime‐sliceexperimentswithvarious93
chlorineandbrominelevels.SinnhuberandMeul[2015]foundcloseragreementina94
simulationwiththechemistryclimatemodel(CCM)EMACtoobservedtrendsof95
globalcolumnozonewhenincludingbrominefromVSLS.96
AnoutstandingissuehasbeenthedifferenceinAntarcticozonerecovery97
projectionsobtainedusingCCMsandprojectionsderivedfromobservations.98
Newmanetal.[2006]usedanobservationallyderivedparametricmodelofozone99
holeareatopredictrecoveryofAntarcticozoneto1980levelsaround2068under100
theAbhalogenscenario[WMO,2003].CCMsusedintheWMO2010Assessment101
[WMO,2011]returnedAntarcticcolumnozoneto1980levelsby2051onaverage,102
muchearlierthanforecastbytheparametricmodel.Thescientificsummary103
suggestedthatfailureoftheparametricmodeltoaccountforanupperstratospheric104
ozoneincrease,whichwouldbecausedbyGHG‐inducedchangesincirculationand105
temperature,couldexplainthisdifference[WMO,2011],.However,Eyringetal.106
[2010]foundonlyasmalldifferenceinOctoberAntarcticozonevaluesfor107
simulationsusingvariousGHGscenarios.108
SignificantlylaterrecoveryofOctoberAntarcticozonewasnotedinChapter109
3ofthe2014WMOOzoneAssessment[WMO,2014]byeachofthefourmodels110
(CMAM,GEOSCCM,UMSLIMCAT,WACCM)thatcontributedsimulationsforthis111
mostrecentAssessment,comparedtoresultsfromalargernumberofmodelsthat112
5
contributedtothe2010Assessment[WMO,2011].However,theywereunableto113
explainthecauseofthelaterrecovery,giventhemodelsimulationsavailableatthe114
time.Themulti‐modelmeanoftheselatestsimulationsindicatedthatreturnof115
AntarcticO3to1980levelswouldnotoccuruntilafter2080.Smalldifferencesinthe116
baseozonedepletingsubstance(ODS)scenariorelativetothatusedintheprior117
Assessment[VeldersandDaniel,2014]causedasmall3‐4%increaseinvortexClyin118
thelaterhalfofthe21stcenturyfortheupdatedsimulations[OmanandDouglass,119
2014]anddonotexplainthelaterrecovery.However,allofthenewsimulations120
representedtheimpactofVSLSonstratosphericBryintheformofaconstant,extra121
5pptofbromine(note:VSLSbromineisindependentofODSspecifications,since122
theVSLSarebiogenicandnotanthropogenic).TheimpactofVSLS‐basedBryon123
ozonerecoverywasnotsimulatedinthe2010Assessment.124
HereweusetheGEOSCCM,whichcontributedtoboththe2010and2014125
WMOAssessments,toquantifytheeffectofanadditional5pptofstratospheric126
brominefromVSLSonboththerecoveryoftheozonelayeroverthe21stcentury127
andthecurrentseasonalevolutionoftheAntarcticozonehole.Weuse5pptfor128
VSLSbrominebecausethisisthebestestimategivenbyWMO[2014].Weshowthat129
inclusionofbrominefromVSLSpartlyexplainswhythe2014Assessmentreported130
asignificantdelayintherecoveryoftheAntarcticozonelayer.Section2describes131
themodelandforcingscenariosaswellasthemeasurementsusedtoevaluatethe132
effectofthisadditionalbromine.Resultsofthesesimulationsandconclusions133
follow.134
135
6
2. Model,ForcingScenarios,andObservations136
TheGEOSCCMcoupledtothestratosphericchemistrymodule,StratChem137
[Pawsonetal.,2008;OmanandDouglass,2014],wasusedtoquantifytheimpactof138
includingVSLSbromineontheozonelayer,focusingontheeffectsoverAntarctica.139
Themodelwasrunat2°2.5°(lat.long.)horizontalresolutionwith72vertical140
layersfromthesurfaceupto80km,withphotochemicalinputdatafromJPL2010141
[Sanderetal.,2011].EvaluationofGEOSCCMusingprocess‐orienteddiagnostics142
wasconductedinbothCCMVal‐1[Eryingetal.,2006]andCCMVal‐2[SPARCCCMVal143
2010].GEOSCCMperformedwellinbothchemicalandtransportrelatedprocesses144
[SPARCCCMVal2010;Strahanetal.,2011;Douglassetal.,2012]andsome145
additionalimprovementswerereportedinOmanandDouglass[2014].146
BothGEOSCCMsimulationsdescribedhereusedGHGconcentrationsfromthe147
RepresentativeConcentrationPathway(RCP)6.0,whichproduces6.0W/m2148
anthropogenicradiativeforcingofclimateby2100[Meinshausenetal.,2011;Moss149
etal.,2010].BothusedtheA12014scenarioforODS[VeldersandDaniel,2014],the150
sameasusedinthe2014WMOAssessment[WMO,2014].Thefirstofthese,the151
controlsimulation(A12014_0Br),doesnotincludeanyBryfromVSLS,asassumed152
forthe2010WMO[WMO,2011]andearlierAssessments.Thesecondsimulation153
(A12014_5Br)includesanextra5pptofCH3BrtorepresentVSLS,asrecommended154
bytheChemistryClimateModelingInitiative(CCMI)[Eyringetal.,2013b].155
Seasurfacetemperatureandseaiceconcentrationswereprescribedfroma156
simulationusingtheCommunityEarthSystemModelversion1(CESM1)conducted157
from1960‐2099[Gentetal.,2011],forcedwiththesameRCP6.0GHGscenario.158
7
ObservationsfromtheOzoneMonitoringInstrument(OMI)andMicrowaveLimb159
Sounder(MLS)ontheNASAAurasatelliteareusedtoevaluatethesimulationof160
ozoneandbrominemonoxide(BrO)fromJan.2005toDec.2015.OMIlevel‐3161
griddeddailytotalcolumnozonevaluesaredeterminedusingtheOMTO3version162
8.5retrievalalgorithm(Bhartia,2007).Inaddition,verticaldailyozone163
measurementsfromMLSlevel‐2version4.2[Liveseyetal.,2015]wereusedinthe164
evaluation.Descriptionandaccesstothesesatellitedatarecordsisat165
http://disc.sci.gsfc.nasa.gov/Aura.166
ForthecomparisonofmodeledandmeasuredBrO,modeloutputissampled167
atthelocationsforwhichOMImeasurementsareavailable.Duetothedielcycleof168
BrO,modeloutputwassamplingat2p.m.localsolartime,closetothetimeofOMI169
overpass.Version3retrievalsoftotalcolumnBrOfromOMIwereusedfor170
comparisonwiththeGEOSCCMoutput;dataanddescriptionareat171
http://disc.sci.gsfc.nasa.gov/Aura/data‐holdings/OMI/ombro_v003.shtml.172
Destriped,level‐2totalcolumnobservations(OMBRO.003)and1σuncertainties173
(basedonspectralfitting)werefilteredusingflags“xtrackqualityflag”toaccountfor174
theOMIrowanomalyand“maindataqualityflag”toremoveinvaliddata.The175
filtereddatawerethengriddedtomatchthelatitudesandlongitudesofthe176
GEOSCCMsimulations.Daily,griddedsatelliteobservationsoftotalcolumnBrOand177
theassociateduncertaintywerecosineweightedandaveragedbetween60to90°S.178
Similarly,GEOSCCMoutputat2p.m.wasweightedandaveraged,butonlyforthose179
modelgridpointswherecorrespondingobservationswereavailable.Finally,time180
seriesofseasonalaverages(JJA)weregeneratedformodeledtotalcolumnBrO,as181
8
wellasforsatelliteobservationanduncertaintyoftotalcolumnBrO.182
183
3.Results/Discussion184
Here,weshowthatinclusionof5pptofCH3Brtorepresentthebrominefrom185
VSLSimpactsboththepresentseasonalevolutionoftheAntarcticozonelayerand186
itsrecoveryoverthe21stcentury.Thesimulatedpresentdayseasonalcycleof187
ozoneoverAntarcticacomparesbetterwithOMItotalcolumnozonemeasurements188
whentheVSLScontributionisincluded.Figure1showsthedailyaveragetotal189
columnozone(DU)amountsfrom60‐90°SfortheA12014_5Br(bluecurve)and190
A12014_0Br(redcurve)simulationsandfromOMIobservations(blackcurve),with191
bothobservationsandsimulationsaveragedover2005‐2015.Theadditional192
brominedecreasesozonebetween6‐20DU,withthelargestdeclineoccurringin193
September.Thefasteronsetoftheozoneholeformationandtheminimumozone194
amounts,around1Octoberareinbetteragreementwithobservationthanfound195
usingthesimulationwithoutVSLSbromine.GEOSCCMdoeshaveasomewhat196
delayedbreakupofthepolarvortex,whichisseenintheslowerozoneincrease197
duringNovemberandDecember.198
ItiswellknownthatozonedeepintheAntarcticpolarvortexbetween14‐18199
kmdropstonearzerolevels,typicallyinthelastweekofSeptemberandthefirst200
weekofOctober[Hofmannetal.,1997].Figure2showsthedailyozonepartial201
pressure(millipascals)at80°SforthesimulationsA12014_5BrandA12014_0Br,202
andMLSozonefrom1Septemberto30October,allaveragedover2005‐2009.The203
simulationincludingVSLSbromineismuchclosertotheverylowabundanceof204
9
ozoneobservedfromMLSandtheSouthPoleozonesonderecordinthelower205
stratosphere,withthenearzerovaluesroutinelyreachedduringthemid‐late1990s206
andearly2000s.ThesenearzerovaluesarenotseentheA12014_0Brsimulation.207
Theozoneprofiledifference(%)betweenthesetwosimulationsandMLS208
observationsover60to82°S,forafewselectdayssurroundingtheozoneminimum,209
isshowninFigureS1.Thiscomparisonalsoshowsimprovedagreementbetween210
pressuresof200to10hPawhentheVSLSsourceof5pptofbromineisincluded.211
OctoberaverageAntarctictotalcolumnozoneisthecommonlyusedmeasure212
ofozonedepletionandrecoveryinWMOOzoneAssessmentsandtheSPARC213
CCMVal‐2Report(SPARCCCMVal,2010).Figure3showstheOctoberaveragetotal214
columnozone(DU)over60‐90°Sfrom1960‐2099forourtwosimulations.The215
A12014_5BrsimulationshowsalmostadecadelaterrecoveryofAntarcticpolar216
ozoneto1980levels.Asexpected,thelargestozonedifferencesbetweenthesetwo217
simulationsoccurwhenchlorineloadinglevelsarewithin50%ofthemaximum.218
GEOSCCMOctobertotalcolumnozonereturnsto1980levelsbyapproximately219
2062intheA12014_0Brsimulationandaround2071intheA12014_5Brsimulation.220
Thesesimulationsrepresentapairofruns,thedifferencebetweenthesetwo221
simulationscouldbeamplifiedofdampedbynaturalinternalvariability.However,222
therecoverydateisalsodelayedbyoveradecadeforthefourmodelsthatincluded223
VSLSbromineforthe2014assessmentbutnotfor2010.Therefore,weexpectthat224
thesignificantdifferencebetweenourpairofsimulationswouldpersistover225
multipleensemblemembers.Thislaterrecoverydateisnowsimilartotheestimate226
fromaparametricmodel[Newmanetal.,2006]usingavailabledataatthetimeand227
10
resolvesadiscrepancybetweenitandrecoveryestimatesfrompreviousWMO228
Assessments[2011].229
ComparisonsoftotalcolumnBrOretrievedfromtheOMIinstrumentwith230
simulatedBrOcolumnssupportsinclusionofacontributionofVSLS,similarto231
resultsobtainedbySalawitchetal.[2010]andLiangetal.[2014].FigureS2shows232
totalcolumnBrOfromOMIaveragedoverthemonthsofJunetoAugust,for60to233
90°S,fortheyears2005to2015comparedtoGEOSCCMsimulationsforthesame234
months,latituderange,andyear.Inclusionoftheextra5pptofbrominereduces,235
butdoesnotcompletelyeliminate,asystematiclowbiasbetweensimulatedand236
observedcolumnBrO.EnhancedtroposphericBrOfromsurfacereleaseisnot237
includedinourGEOSCCMsimulations,whichcouldaccountforthelowbiasin238
modeledBrO.Roscoeetal.[2014]showsurfacereleaseofbrominetypically239
contributesbetween1and31013molcm2oftroposphericBrO,distributed240
throughoutthefreetroposphere,atHalleyBay(75.6°S).Anotherpossibilityforthe241
underestimateofcolumnBrOcouldbemodelmisrepresentationoftheBrO/Bryin242
thetroposphere.Ontheotherhand,theactualcontributionfromVSLSto243
stratosphericBrycouldbelargerthan5ppt.TheresultspresentedinFigureS2are244
consistentwithestimatesofatleast5pptofbrominebeingsuppliedbyVSLS245
[Salawitchetal.,2005;Dorfetal.,2008;Theysetal.,2007;Salawitchetal.,2010;246
Parrellaetal.,2013,Liangetal.,2014].247
TimeseriesofBrO,BrCl,andOClOat50hPafromthetwoGEOSCCM248
simulations,averagedover60‐90°SduringAug.‐OctareshowninFigureS3.Neither249
BrO,BrCl,norOClOreturntotheirrespective1980levelsbytheendofthe250
11
simulations.ThetimeseriesofOClObehavesinasimilarmannertoBrOandBrCl251
becausetheabundanceofOClOinthepolarvortexismuchmoresensitivetoBrO252
thanClO[Salawitchetal.,1988].Thedifferencebetweenthetwosimulationsgrows253
largerwithtime,reflectingamuchlargerroleforozonelossduetotheBrO+ClO254
cycleinA12014_5BrthantheA12014_0Brsimulationduringthelatterpartofthis255
century.Together,Figures3,S2,andS3showthatincludingallthesourcesof256
stratosphericbrominecausesaboutadecadedelayintherecoveryoftheAntarctic257
ozonehole.258
IncludingsupplyofstratosphericbrominefromVSLSreducesozonecolumns259
nearlyeverywhereinthemodel,withthesmallestchangesinthetropicsandthe260
largestdecreasesoverthehighlatitudesduringspring(Figure4).Theeffectofthis261
extrabromineislargestduringthetimeperiodofpeakchlorine(1990–2019).For262
thisthree‐decadeperiod,inclusionofBryfromVSLSdecreasestotalcolumnozone263
by16‐22DUoverAntarcticaduringSeptember.IntheNorthernHemispherehigh264
latitudes,ozoneisreducedby10‐20DUduringMarch.Thetropicaltotalcolumn265
ozonedecreaseistypicallylessthan2DU.Thisthree‐decadetimeperiodalso266
includestheeruptionofMt.PinatuboinJune1991,shortlyafterwhichozoneloss267
duetobrominewaslargerintheA1204_5Brsimulation.However,theenhanced268
ozonelossfollowingtheeruptionofMtPinatubofollowstheaerosollifetimeinthe269
stratosphereof1‐3yearsanddoesnotsignificantlyimpactthe30‐yearaverage270
response.271
272
4.Conclusions273
12
Inclusionof5pptofstratosphericbrominetorepresentVSLSinGEOSCCM274
resultsinbetteragreementwithOMImeasurementoftotalcolumnBrOandcauses275
severalimportantchangesinthesimulationoftheseasonalevolutionandrecovery276
overthe21stcenturyofAntarcticozone.AhighbiasinsimulatedSHpolartotal277
columnozonewithrespecttoOMIobservationscollectedover2005to2015is278
significantlyreduced.IncludingVSLSbrominecausestheminimumseasonalozone279
columntooccuraboutaweekearlier,incloseragreementwithOMIobservations.280
TheverylowtonearzeroozoneconcentrationsobservedinthedeepAntarctic281
lowerstratosphericpolarvortexduringlateSeptemberintoearlyOctoberduring282
themid‐late1990sandintotheearly2000sareonlysimulatedwhentheVSLS283
brominesourceisincluded.284
AccordingtoourGEOSCCMsimulations,recoveryofAntarcticozoneis285
delayedbyaboutadecadeuponincludingtheVSLScontributiontostratospheric286
bromine.OctoberAntarcticozonecolumnsareprojectedtoreturnto1980levels287
around2071,incloseagreementwitharecoveryyearof2068basedonan288
empirical,parametricmodel[Newmanetal.,2006].The2010WMOAssessment289
[WMO,2011]attributedanearlierrecoveryyearof~2051,providedbysimulations290
from17CCMs,tometeorologicalanddynamicaleffectsofGHGsonAntarcticozone291
thatwerenotconsideredintheparametricmodel.However,mostoftheCCM292
simulationsusedinWMO[2011]neglectedVSLSbromineandWMO[2014]showed293
themeteorologicalanddynamicaleffectsofGHGsonAntarcticozonerecoverywas294
small.Theseresultsshowthataconstantadditionof5pptofbrominecausealmost295
adecadelaterrecoveryofAntarcticozoneandsuggestthatanyfuturegrowthor296
13
newemissionsofbrominecontainingcompounds,aslowasacoupleppt,could297
significantlyimpacttheprojectedozonerecoverydate.Ourstudyalsosuggests298
modelsestimatesofpolarozonerecoveryforthenextAssessmentshouldincludea299
realistictreatmentoftheVSLScontributiontostratosphericbromine.Ifbromine300
fromVSLSareneglected,recoverydateswillbebiasedearlybyperhapsasmuchas301
adecade.302
303
Acknowledgements304
We thank the NASA ACMAP, Aura, and MAP program for supporting this305
research. We would like to thank two anonymous reviewers for their helpful306
commentsandsuggestiontoimprovethismanuscript.Wealsothankthoseinvolved307
in model development at GSFC, and high‐performance computing resources308
providedbyNASA’sAdvancedSupercomputing(NAS)DivisionandtheNASACenter309
forClimateSimulation(NCCS).Alldataandmodeloutputusedinthesefigureswill310
beavailablewiththe linktothispublicationat theGEOSCCMwebsite(http://acd‐311
ext.gsfc.nasa.gov/Projects/GEOSCCM/), additional information is available by312
contactingthecorrespondingauthor([email protected]).313
314
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Figures455456457458
459460Figure1.Thedailyaveragetotalcolumnozone(DU)between60‐90Sfor2005‐4612015.ThebluecurveshowstheA12014_5Brsimulation,theredcurveisthe462A12014_0Brsimulation,andtheblackcurveistheOMIobservation.Adashedblack463lineshows1October.464465
21
466467Figure2.Dailyozonepartialpressure(millipascals)at80°Sfora)A12014_5Br,b)468A12014_0Br,andc)MLSmeasurementsfrom1Septemberto30Octoberaveraged469over2005‐2009.Thecontourintervalis0.25between0and1and0.5between1470and3and1above3.471472
22
473474475Figure3.TheOctoberaveragetotalcolumnozone(DU)between60‐90Sfrom1960476to2099.Thebluecurvesshowtheindividualyearvalues(thin)andlowpass477filteredvalues(thick)forthesimulationwithanextra5pptofbromine.Thered478curvesshowtheindividualyearvalues(thin)andlowpassfilteredvalues(thick)for479thesimulationwithoutarepresentationofbrominefromVSLS.Theverticaldashed480redandblacklinesrepresentthereturnto1980levelsusingthesmoothedcurves481withouttheextraBrandthesimulationwiththeextraBr.482 483
23
484Figure4.Thelatitudebymonthtotalcolumnozone(DU)fortheA12014_5Br(top485panel)andA12014_0Br(middlepanel)simulationsaverageover1990‐2019.The486bottompanelshowsthedifferenceintotalcolumnozone(DU)betweenthetwo487simulations.488489