Responsetorefereecommentson:StudyingtheimpactofbiomassburningaerosolradiativeandclimateeffectsontheAmazonrainforestproductivitywithanEarthSystemModel.Ref:acp-2018-924Firstly,wewouldliketothankthereviewersfortheirtimeandtheirconstructivecommentsonthemanuscript.Wearegladthatthereviewersfindthepaperwell-writtenandofinteresttothescientificcommunity.Belowpleasefindourresponses(inblue)toallreviewercomments(inblack).WehopethattheupdatedversionofourmanuscriptisnowsuitableforpublicationinAtmospheric,ChemistryandPhysics.Allthebest,FlorentMalavelleonbehalfofallco-authors.

AnonymousReferee#1

Receivedandpublished:9November2018

ThisstudyusesacoupledmodellingframeworkbasedontheHadGEM2-ESEarthSystemmodeltoquantifytheeffectofAmazonregionbiomassburningaerosolontheterrestrialcarboncyclethroughchangesindirectanddiffusesurfaceradiationandfeedbackfromclimateadjustments.AssessingtheabilityofEarthSystemmodelstofullysimulatesucheffectsisveryimportantandthisstudyisatimelyandwelcomeadditiontoexistingworkinthisarea-especiallyasothercoupledmodelstudiesinvestigatingdiffusefertilisationeffectsarebasedonadifferentmodel.Themanuscripthasaverygoodstructureandisgenerallywellwritten.

IhaveafewcommentsandrecommendationsthatIwouldliketoseeaddressedbeforepublication.

Specificcomments:

1.ItisnotclearwhytheauthorschosetousetheCLASSICaerosolschemetorepresentaerosolsintheirmodel,insteadofthemodalaerosolmicrophysicsscheme(GLOMAP-mode)whichhasalreadybeenimplemented,testedandwidelyusedinHadGEMmodels.AsshowninBellouinetal.(2013),GLOMAP-modeprovidesabetteragreementwithaerosolobservationsandre-analysisproductsthantheCLASSICscheme.Thesamestudyalsofoundsubstantialdifferencesinaerosoldirectradiativeforcingestimatesbetweenthetwoschemes,i.e.-0.49Wm-2forGLOMAP-modevs.-0.18Wm-2forCLASSIC;suchdifferencesarelikelytohaveanimportantimpactondiffusefertilisationeffectestimates.Ifitisunfeasibletorepeatsimulationsalsousingthemodalscheme,couldtheauthorscommentonthepotentialuncertaintyassociatedwiththeuseoftheCLASSICschemeandmaybeevenestimatethisuncertainty?

WeusedHadGEM2-ESbecause:i)wewantedtobeconsistentwithPacificoetal.(2015)andii)wewantedaconfigurationforourEarthSystemModelthatisrobust,wellcharacterisedandscientificallycomparablewithpastpublishedstudies.Thiswasn’tpossiblewithHadGEM3whenouranalysisstartedasHadGEM3wasstillinitsinfancy(onemightargueitisstillasUKESMwillbethemaincontributionfromtheUKtoCMIP6).HadGEM2-ESstillrepresentsthestate-of-the-art.GLOMAP-modewasimplementedwithinUKCAinHadGEM3,itisthereforenotavailableinHadGEM2-ES.ThatiswhyweusedtheCLASSICaerosolschemeinthepresentstudy.Back-portingthispartofthecodeisunlikelytobefeasibleinatimelymannerandwouldbeaverytime-consumingtaskandisnotconsideredworthwhile.

Radiativeforcing(RF)maynotbetheidealmetricfordiscussingproandconsofGLOMAP-ModevsCLASSIChere.Firsttheseareglobalaverages.Secondly,aerosolRFisRFduetotheanthropogenicfractionoftheaerosol.Thirdly,RFiscalculatedasadifferencebetweenpresent-day(PD)andpre-

industrial(PI).AsactuallyhighlightedbyBellouinetal.(2013)“theimportanceofthe1850baselinehighlightshowmodelskillinpredictingpresent-dayaerosoldoesnotguaranteereliableforcingestimates”.

Thatbeingsaid,thisaspectofchoosingaspecificaerosolrepresentation(CLASSICvsGLOMAP-Mode)shouldnotaffectourresultssignificantly.Asarguedintheresponsetothenextcomment,tothefirstorder(assumingtherepresentationofvegetationprocessesisappropriate),investigationoftheimpactofBBAonvegetationonlyreallyrequiresaccuratesimulationofAOTs(i.e.thequantitythatcontrolsthedirectaerosolradiativeeffect).CLASSICistotallycapableofprovidingaccurateAOTs(asdepictedonFig2inthemainmanuscript)overtheregionstudiedandtheradiativetransferrepresentationhasn’tchangedsubstantiallybetweenHadGEM2andHadGEM3.

AnadditionpointregardingtheuseofCLASSICvsGLOMAPmode.Bellouinetal.(2013)usedadevelopmentalversionofHadGEM3.Theuseofdevelopmentalschemes,whileunderstandable,leadstosomedifferentresultsandconclusions.Indeed,amorerecentpublicationwhichfocussesonbiomassburningbyJohnsonetal.(2016)providesamoreup-to-dateassessmentofthedifferencesbetweenCLASSICandGLOMAP-modewithaspecificfocusonbiomassburningaerosols.ThereviewershouldalsokeepinmindthatthedifferencesinradiativeforcingthataredocumentedinBellouinetal(2013)arepresent-day–pre-industrial;wearefocussedonscalingpresentdayemissions,whichisratherdifferent.Indeed,Johnsonetal(2016)showthattheimpactoftheschemesforbiomassburningaerosolintheirbaseformisactuallyratherlittleovertheAmazonianregion.ThisisevidentinFigure2and3ofJohnsonetal(2016)whichareincludedbelowforthereviewer’sconvenienceforannualmeanandforSeptember(peakofBBseasonrespectively):

Fig2fromJohnsonetal.(2016).Annualmean.

Fig3fromJohnsonetal.(2016).Septembermean.

ItisdifficulttoseesignificantdifferencesintheAOD,andevenmoredifficulttosaywhichis‘better’whencomparedagainste.g.MODISobservationsoverSouthAmerica(Fig3fromJohnsonetal.2016).

Fig3fromJohnsonetal.(2016).ComparisonofCLASSICandGLOMAP-modetotalaerosolcomparedagainst

C5andC6datafromMODIS(Johnsonetal.,2016)

Johnsonetal.(2016)alsoevaluatedifferenceine.g.,thesinglescatteringalbedoetcbetweenCLASSICandGLOMAP-Mode.Owingtoupdatesinabsorptionpropertiesandformulationintheschemes,differencesarerelativelymarginal.GenerallyCLASSICisabletorepresentaerosoldirecteffectswithfidelitybecause,althoughitisasinglemomentscheme(prognosticmassonly),aerosolmicrophysicalpropertiesandhencetheopticalparametersarebasedonaircraft-basedobservationsofbiomassburningaerosol.However,weagreewiththereviewerthattheindirectradiativeeffectsfromsinglemomentschemescanberadicallydifferentfromthosefromdualmomentschemeslikeGLOMAP-mode(asincreasesinaerosolmassdonotnecessarilyincreasetheaerosolnumberandhenceCCN,Malavelleetal.2017).

• Bellouin,N., et al., Impact of themodal aerosol schemeGLOMAP-mode on aerosol forcing in theHadleyCentreGlobalEnvironmentalModel,Atmos.Chem.Phys.,13,3027–3044,(2013).

• Johnson,B.T.,Haywood,J.M.,Langridge,J.M.,Darbyshire,E.,Morgan,W.T.,Szpek,K.,Brooke,J.K.,Marenco,F.,Coe,H.,Artaxo,P.,Longo,K.M.,Mulcahy,J.P.,Mann,G.W.,Dalvi,M.,andBellouin,N.:EvaluationofbiomassburningaerosolsintheHadGEM3climatemodelwithobservationsfromtheSAMBBA field campaign, Atmos. Chem. Phys., 16, 14657-14685, https://doi.org/10.5194/acp-16-14657-2016,(2016).

• Malavelle, F. F. et al., Strong constraints on aerosol–cloud interactions from volcanic eruptions,Nature,546,(2017).

2.ImighthavemisreadSection2.2,butaccordingtothefirstparagraph,year2000fireemissionshavebeenusedinallsimulations.RecordlowfireshavebeenrecordedthroughouttheAmazonregionduringyear2000,seee.g.Table7invanderWerfetal.(2010):137TgCyr-1ofSouthernHemisphereSouthAmericanfireemissions,i.e.∼50%ofthe271TgCyr-11997-2009mean.Pleaseclarifyexactlywhatfireemissionshavebeenusedinyoursimulations(alsostatingtheregionalamountsoffireemission).Ifitisonlyyear2000,thanadetaileddiscussionisneededoninterannualvariabilityandtheextenttowhichthelowfiresfromyear2000arerepresentativeforpresentday.

TheBBAemissionsusedherearenottheemissionsfortheexactyear2000butadecadalmeancentredon2000.ThisismentionedatP8,Lines15-16:

“AerosolandtheirprecursoremissionsaretakenfromtheCMIP5inventories(Lamarqueetal.,2010).Weusethedecadalmeanemissionscentredaroundtheyear2000representativeofpresent-dayemissions”

ThebiomassburningemissionsusedduringCMIP5arebasedontheGFEDv2inventory(vanderWerfetal.,2006)forthe1997–2006period.AsdetailedinLamarqueetal.(2010):“Giventhesubstantialinterannualvariabilityofbiomassburningonaglobalandregionalscale(e.g.,Duncanetal.,2003;Schultzetal.,2008),itisproblematictouseasnapshotdatasetfromanindividualyearforthedevelopmentofadatasetthatisconsideredtoberepresentativeforadecade.[…]forthe2000estimatewhichiscalculatedfromthe1997–2006average.”

WehavemodifiedP8,Lines20-23tomakethisclearer:

“AerosolandtheirprecursoremissionsarethedatasetusedduringCMIP5(Lamarqueetal.,2010).[…]Giventhesubstantialinterannualvariabilityofbiomassburningonaglobalandregionalscale,apresent-dayclimatology(i.e.averageyear)iscalculatedastheGFEDv21997-2006average(Lamarqueetal.,2010).

NotethatthereasonforvaryingaerosolemissionswastoaccountforthevariabilityinBBAsourcesandintensity.ThesevariationsarereadilyvisiblefromtheMODISAOTretrievalswhenlookingattheindividualyearsbetween2001and2016(Fig.2binthemainmanuscript).TheemissionmultiplicationfactorswerethereforeconsideredsuchasHadGEM2couldrepresentasimilarrangeofAOTs.AOTisthequantityusedbytheradiativetransferandisresponsibleoftheaerosoldirectradiativeeffectswhicheventuallyaffectvegetation.WethereforefavouredconstrainingBBAviathe‘optics’inHadGEM2ratherthanviaemissionsasdiscrepanciesinmodelledparticulatematterandmodelledAOTareacommonfeatureofaerosolmodels(includingGLOMAP-Mode,e.g.Reddingtonetal.2016,2018).

• Reddington,C.L., Spracklen,D.V.,Artaxo,P.,Ridley,D.A.,Rizzo,L.V.,andArana,A.:Analysisofparticulateemissions fromtropicalbiomassburningusingaglobalaerosolmodeland long-termsurfaceobservations,Atmos.Chem.Phys.,16,11083-11106,https://doi.org/10.5194/acp-16-11083-2016,2016.

• Reddington,C.L.,Morgan,W.T.,Darbyshire,E.,Brito,J.,Coe,H.,Artaxo,P.,Marsham,J.,andSpracklen,D. V.: Biomass burning aerosol over the Amazon: analysis of aircraft, surface and satelliteobservationsusingaglobalaerosolmodel,Atmos.Chem.Phys.Discuss.,https://doi.org/10.5194/acp-2018-849,inreview,2018.

3a.Towhatextentistheorderofswitchingoffthe3mechanismsimportant(Table3showingtheexperimentaldesign)?Whatisthemagnitudeofthe3effectsifyouestimatetheminadifferentway:forexampleonpage14,retrievingdelta_NPP_climbycontrastingNPPˆBBAx1_clim.aer,Tot.aer,FD.aerwithNPPˆBBAx0_clim.aer,Tot.aer,FD.aer?

Thisisagoodquestion.Itwillbeaddressedinthenextcommentasouranswercoversbothcomments3aand3b.

3b.Regardingyourassumptiononpage12,line25,namely“neglectingtheinterdependencybetweenthethreeterms”,towhatextentisthistrue?Canyouconfirmwithyoursimulationsthattheoveralleffectisthesumofthe3individualeffects?

Thisisaverygoodquestiontoo.Weanswerthisasfollows:

Wewillstartbyansweringthesuggestionofusingtheterm[NPPˆBBAx1_clim.aer,TotPAR.aer,Fd.aer-NPPˆBBAx0_clim.aer,TotPAR.aer,Fd.aer]asanalternativewaytoretrieved_NPP_clim(comment3a).ThistermactuallycorrespondstotheneteffectofBBAonthevegetation(i.e.firsttermontheLHSineq.4),soitincludesboththeeffectofthefastclimateadjustmentsandeffectofchangesinradiationduetotheBBA.

Theequation3fromthemainmanuscriptisreproducedbelow:

𝛿𝑁𝑃𝑃 ≅𝜕𝑁𝑃𝑃𝜕𝑓'

𝛿𝑓' +𝜕𝑁𝑃𝑃

𝜕𝑇𝑜𝑡𝑃𝐴𝑅 𝛿𝑇𝑜𝑡𝑃𝐴𝑅 +𝜕𝑁𝑃𝑃𝜕𝐶𝑙𝑖𝑚 𝛿𝐶𝑙𝑖𝑚

Notethatweusedthesymbol≅insteadofastrictequalityaswehaveneglectedthehigherordertermshere.Thisisnowwrittenthiswayinthemanuscript.

ThisequationcanbeinterpretedinanEffectiveRadiativeForcing(ERF)framework.ThenetchangeinNPP(thetermonLHS)istheresultofthecontributionofi)theaerosoldirectradiativeeffect(i.e.thechangeinradiationseenbythevegetationrepresentedbythetwofirsttermsontheRHS)andii)thefastclimateadjustmentsduetotheaerosolforcing(i.e.the3rdtermontheRHS).Inacondensedform,eq.3canberewrittenasfollow:

𝛿𝑁𝑃𝑃 ≅𝜕𝑁𝑃𝑃

𝜕Radiation𝛿𝑅𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 +𝜕𝑁𝑃𝑃𝜕𝐶𝑙𝑖𝑚 𝛿𝐶𝑙𝑖𝑚

WhereRadiationcontainstheeffectofchangesinTotPARandthediffusefraction(fd).Thetwocontributions(δRadiationandδClim)canbeassessedindependentlyalthoughthechangesoftheclimatecanslightlyaffectthevaluesoffdandTotPAR(e.g.viachangesincloudiness,moreonthislater).

Thefirstterm(δRadiation)iscalculatedateachmodeltime-step(i.e.forafixedclimate)whereasthesecondterm(δClim)iscalculatedfromapairofsimulationswheretheeffectofaerosolsontheradiationseenbythevegetationarenotconsidered(i.e.𝑇𝑜𝑡𝑃𝐴𝑅 = 𝑐𝑙𝑒𝑎𝑛, 𝐹𝑑 = 𝑐𝑙𝑒𝑎𝑛).

Thecontributionofthefastclimateadjustmentstotheaerosolforcing(δClim)isevaluatedusingeq.7.Analternativewritingforeq.7innumericalformthatisconsistentwitheq.5andeq.6isasfollows:

∆𝑁𝑃𝑃CCCCCCDEFGHHIJK = L𝑁𝑃𝑃CCCCCCMEFG.OPQ,RST.DEPOU,V'.DEPOUHHIJK −𝑁𝑃𝑃CCCCCCMEFG.XYZ[\,RST.DEPOU,V'.DEPOUHHIJK ]−L𝑁𝑃𝑃CCCCCCMEFG.OPQ,RST.DEPOU,V'.DEPOUHHIJ^ −𝑁𝑃𝑃CCCCCCMEFG.XYZ[\,RST.DEPOU,V'.DEPOUHHIJ^ ]

Asclim.cleancorrespondstotheclimatethathasnotexperiencedanyaerosolradiativeforcing,theterms𝑁𝑃𝑃CCCCCCMEFG.XYZ[\,RST.DEPOU,V'.DEPOUHHIJK and𝑁𝑃𝑃CCCCCCMEFG.XYZ[\,RST.DEPOU,V'.DEPOUHHIJ^ areeffectivelyequal.ThereforetheclimateeffectofBBAonvegetationcanbesimplifiedtoretrieveeq.7:

∆𝑁𝑃𝑃CCCCCCDEFGHHIJK = _𝑁𝑃𝑃CCCCCCMEFG.OPQ,RST.DEPOU,V'.DEPOUHHIJK ` −_𝑁𝑃𝑃CCCCCCMEFG.OPQ,RST.DEPOU,V'.DEPOUHHIJ^ ̀

WebelievethisisthecleanestestimateoftheimpactofclimateadjustmentsduetotheBBAforcingonthevegetationproductivity.

NowremainsthecalculationofthecontributionfromδRadiation.InthemanuscriptweassumedafirstorderexpansionsowecanevaluateindependentlythecontributionsfromfdandTotPAR,namely:

𝜕𝑁𝑃𝑃𝜕𝑅𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 𝛿𝑅𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 ≅

𝜕𝑁𝑃𝑃𝜕𝑓'

𝛿𝑓' +𝜕𝑁𝑃𝑃

𝜕𝑇𝑜𝑡𝑃𝐴𝑅 𝛿𝑇𝑜𝑡𝑃𝐴𝑅 = 𝐹 + 𝑇

WhereFrepresentstheeffectoffdandTtheeffectofTotPAR.InordertogetthemostaccurateestimationofFandT,theorderofswitchingon/offthe2mechanismsisindeedimportant.WecalculatetheeffectofthereductioninTotPARfirst.Thenwecalculatetheeffectoftheincreaseinfd.DoingtheotherwayaroundwouldgivetoomuchweighttotheDFEasahighfdwithahighTotPARwouldincreasethevegetationproductivityunrealistically(i.e.anincreaseinfdisalwaysconcomitantwithadecreaseinTotPAR).

Inequation3(seebeginningofthislengthyresponse),weneglectedthedependencybetweenfdandTotPARandClim.Theexactvalueofthecontributionof𝛿𝑅𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛couldthereforebewrittenas:

𝜕𝑁𝑃𝑃𝜕𝑅𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 𝛿𝑅𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 =

𝜕𝑁𝑃𝑃𝜕𝑓'

𝛿𝑓' +𝜕𝑁𝑃𝑃

𝜕𝑇𝑜𝑡𝑃𝐴𝑅 𝛿𝑇𝑜𝑡𝑃𝐴𝑅 + 𝑅 = 𝑇𝑅𝑈𝐸_𝑑𝑅𝐴𝐷

WhereRcorrespondstothehigherordercrossedtermsbetweenfdandTotPARandClim.

Inthemanuscript,weprovidedestimatesofFandT.Ifthisfirstorderlinearizationisasuitableapproximation,thenthesumofFandTshouldbeclosetoTRUE_dRAD(i.e.Rissmall).

WithourdiagnosticsweareabletocalculatebothTRUE_dRAD(i.e.bysummingtheeffectoffdandTotPARbeforetemporalandspatialaveraging)andthesumofF+T(i.e.summingthetemporallyandspatiallyaveragedFandT).ThesecalculationshavebeendonefortheNPPoverthedomainofanalysisdefinedinthemanuscript.TheresultsareforthemonthofAugustbuttheseholdfortheothermonths.Resultsareshowninthetablebelow:

d_NPP(wrtBBAX0)inTgC/month F T F+T TRUE_dRAD R

BBAX0.5 13.7 -9.6 4.1 5.0 0.9BBAX1 22.4 -17.9 4.5 5.1 0.6BBAX2 33.5 -35.0 -1.5 -2.5 -1.0BBAX4 41.0 -66.8 -25.8 -34.6 -8.8

TheagreementbetweenF+TandTRUE_dRADisreasonablewhichsupportsthatafirstorderlinearisationisanappropriateapproximation.Itbecomescriticisableforthehighaerosolsimulation(BBAX4)however.Mathematically,itmeansthatthelinearisationstartstobeinaccurateasthedeviationfromthereferencepointbecomeslarge.Physicallyitcanbeexplainedbythesetwomechanisms:

- AsanincreaseinfdisalwaysconcomitantwithadecreaseinTotPAR,thetwovariablesarenottrulyindependent.

- Ifthechangeinclimateisimportant,thereisthepossibilitythatitaffectsfdandToTPAR(e.g.throughchangeincloudinessviaaerosolsemi-directeffects).

Insummary,whenAOTsgetveryhigh,theerrorbetweenF+TandTRUE_dRADislikelytoincrease.

IfthetwocontributionsfromδRadiationandδClimweretrulyindependent,thenaddingthemtogethershouldgiveusthesameamountofchangeinNPPaswhencalculatingthechangesfromeq.4.Toverifythis,wecalculatedthebudgetsinthesimilarwayasthetableabove:

d_NPP(wrtBBAX0)inTgC/month TRUE_dRAD δClim

(eq.7)TRUE_dRAD+δClim

NETd_NPP(eq.4)

Differences(i.e.~R)

BBAX0.5 5.0 20.6 25.6 24.8 -0.8BBAX1 5.1 21.9 27.0 26.4 -0.6BBAX2 -2.5 40.0 37.5 38.6 0.9BBAX4 -34.6 61.1 26.5 35.3 8.8

UnderstandingtheeffectofδclimonδRadiation(e.g.viachangeincloudiness)wouldcertainlybeaninterestingacademicproblembutitwouldbewaybeyondthescopeofthispaperandnotfeasiblewiththesetofsimulationswehaveconducted.Besidesthisseemstobeofsecondorder(asδClim>>TRUE_dRADunlessAOTislarge).

Thebottomlineisthatourconclusionsremainunchanged;wecanseparatethecontributionofthethreetermssafely.Overall,thevariationinradiationarecontributingmuchlesstothechangesinNPPthantheclimateadjustmentsresultingfromtheeffectofBBA.

4.Page4,lines12-13&lines30-31andparagraphstartingonp22,l27:whywastheozonedamageeffectnotincludedinyoursimulations?Asyoumentiononpage5line2,thePacificoetal.(2015)studyusedasimilarmodellingframework(samemodel),soonewouldexpectthatincludingtheeffectshouldberelativelystraight-forward?

Indeed,itwouldbeeasytoaddtheozoneeffectinthecurrentstudy.Thetwostudies(Pacificoetal,andthisone)wereconductedinparallelforthesameprojectthereforethesewereaddressingtwoscientificquestionsseparatelyinordertoconstructagoodunderstandingoftherespectivemechanisms.Besides,ozoneandaerosolseffectswillhaveadifferentspatialfootprint(duetothechemistryofOzone),whichwarrantsstudyingthemindependentlybefore.WearenowanalysingnewESMsimulationsattheglobalscalewhichcombineboththeDFEandtheOzonedamage.Weplantosubmittheseresultsforpublicationinaseparatemanuscript.

Technicalcorrections:

-p1,l23-28:pleaseclearlystatethetimeperiod(year)theestimatedvaluescorrespondto.

Added:“Resultsshowthattheoverallnetimpactofpresent-day,definedasyear2000climate,biomassburningaerosolsistoincreasenetprimaryproductivity(NPP)by…”

Notethatasexplainedinthemethodsection,weuseclimatologicalforcing(includingtheBBAemissions)sowedonotspecificallysimulateagivenyearbutaperiodrepresentativeofthemeanstateoftheEarthclimate.

-p3,l21:“didnotaccounted”->“didnotaccount”.

Modified.-p7,l11-12:pleaserevisesentence–an“and”isprobablymissing.Indeed,sentencealtered:“Transportedspeciesexperienceboundarylayerandconvectivemixing,andareremovedbydryandwetdeposition”

-p8,l24:whatisthereasonbehindapplyingthe“multiplicationfactor”onlyforSouthAmericansources?

Tworeasons:

i) WewantedtobeconsistentwiththePacificoetal.,2015asexplainedabove.ii) WealsomultipliedBBAemissionsgloballyinseparatesimulations.Indoingso,wenoticedthat

thecontributionfromSouthernAfricanfiresovertheAmazonwasnon-negligible.Inaddition,astrongincreaseinglobalBBAemissions(e.g.X2andX4)introducesadditionaleffectsontheglobalclimatesuchasexpansionoftheHadleycells(duetotheabsorbingnatureoftheseaerosols).

-p11,eq(1):pleaseexplicitlystatewhatyoumeanby“dL”.-p11,l26:“analyse”->“analysis”.

dLwasremovedfromtheequation,thatwasinconsistentwritingoftheexponentialdecayprofile.NotationfortheleaflevelNitrogenwasslightlyalteredforimprovedclarity:

𝑁ePOf(L) = 𝑁e^𝑒jkle

-p12,l24-25:Ithinkdeltasaremissing,whenyouwanttodefine“deltaf_d”,“deltaTotPAR”and“deltaclim”.

Inthewaythesentencewasoriginallywritten,youarerightandthedeltasshouldappear.However,theaimwastodefinethenomenclaturethatisusedintheremainderofthemanuscript(e.g.fdfordiffusefraction).Assuchweslightlymodifiedthesentence:

“Asimpletheoreticalframeworkcanbeusedtodiscriminateafastcarbonflux,e.g.NPP,asafunctionofthe‘diffusefraction’,fd,the‘totalPAR’,TotPARandthe‘climatefeedback’,clim,suchasNPP(fd,TotPAR,clim).”

-p15,l12-14:sayingthattherevisedconfigurationprovidesabetterestimateofglobalGPPisprobablytoostrongastatementconsideringtheactualvalues.Also,sinceyourstudyisrestrictedtotheAmazonregion,itwouldbegoodtosaysomethingabouthowthesimulatedGPP/NPPvaluesoverthisregioncomparetoFLUXCOM,Shaoetal(2013)andMODIS.Figure1a-dsuggestsanover-predictionofthemodel(despiteanunder-predictionofglobalGPP)?

Thisisafairpoint.IfweweretoassumethatthebestestimatesitssomewhereinbetweenFLUXCOM(+129PgC/yr)andforShaoetal.(2013,+118PgC/yr),thentheupdatedGPPestimateinHadGEM2(i.e.

+115PgC/yr)sitsslightlycloserthantheestimatefromtheoriginalmodelconfiguration(+140PgC/yr).Indeed,wecanarguethattheunderestimationofGPPintheupdatedHadGEM2configurationiscomparable(inmagnitude)totheoverestimationofGPPintheoriginalHadGEM2configuration.Wehintedtowards‘better’becausetheratioofNPPoverGPPintheupdatedversionofHadGEM2ismoreconsistentwithobservationally-basedratioestimates(e.g.Luyssaertetal.,2007)whereastheoriginalHadGEM2configurationhadtoolowNPP/GPPratios.Giventhelargeuncertaintiesinalltheseestimates,‘better’isprobablyabitofastretchsowehavemodifiedthetextaccordingly.InadditionwequantifiedtheGPPmorespecificallyfortheAmazonregionassuggested.

“TheunderestimationoftheGPPintheupdatedHadGEM2-ESconfigurationiscomparableinmagnitudetotheoverestimationoftheGPPintheHadGEM2-ESconfiguration.However,theratioofNPPoverGPP(notshown)intheupdatedversionofHadGEM2ismoreconsistentwithobservationally-basedratioestimates(e.g.Luyssaertetal.,2007).DespitetheinherentuncertaintiesinthetworeferenceestimatesoftheglobalGPP(i.e.between+118and129TgC/yr),itsuggeststhattheupdatedversionofHadGEM2-ESisabletoprovideamoreconsistentglobalGPPestimate.OverthecentralAmazondomainwhichisrepresentedbytheregionencapsulatedintheredboxonFig.2a.,HadGEM2-ESaveragedGPPinAugust(respectivelySeptember)is2750±250gC/m2/yr(respectively2600±200gC/m2/yrforSeptember)comparedto2250±125gC/m2/yr(respectively2500±180gC/m2/sforSeptember)forFLUXCOM.[…]DespiteobviousoverestimationbyHadGEM2-ESoftheNPPonannualmeanoverSouthAmericawhencomparedtoMOD17A2(Fig.1band1d)thefluxesarewellcapturedduringthepeakofthefireseasonoverthecentralAmazon.TheaverageGPPfromHadGEM2-ESinAugust(respectivelySeptember)is1080±140gC/m2/yr(respectively975±100gC/m2/yrforSeptember)comparedto990±550gC/m2/yr(respectively1025±590gC/m2/sforSeptember)forMOD17A2.“

-p15,l27-30:alreadydescribedwithinthefigurecaption,sononeedtoalsodescribewithinthetextwhateachlinerepresents.

Redundantfiguredescriptionremovedfrommaintext.

-p19,l21:abitconfusing,asintheFig.8captionyoudescribethelineas“grey”ratherthan“black”.Again,besttodescribefigureinthecaptionandonlydiscussininthetext.

Redundantfiguredescriptionremovedfrommaintext.Wechangedthecolournameto‘darkgrey’inthelegendoffig.8.

-p20,l17:youmighthavereversedABS_OPandDIFF_OP(less/morescattering).

Wellspotted.Ithasbeencorrected.

-p20,l23-27:pleasegiveexactvalueshere,asit’snotclearwhatyoumeanby“significantchange”soit’sbesttohaveactualvalueshere.

Wehaveaddedadiscussionwithmorequantifiedsubstance:

“However,wedonotobserveasignificantchangeinthemodelledBBAimpactonvegetationproductivityforthevaryingBBAscattering/absorbingassumptions(Fig.9b).Inthestandardsimulations,thenetchangeinNPPduetoBBAis+28.4to38.6TgC/monthinAugust.FortheDIFF_OPsimulation(respectivelyABS_OP)thenetchangeinNPPis+32.1to36.2TgC/month(respectively+17.9to18.2TgC/month).ForSeptember(notshown),weactuallyfoundthattheABS_OPsimulationhadthelargestincreaseinNPPwhichisnotconsistentwithourassumption.Insummary,theeffectofBBAopticalpropertiesonNPPchangesarewithinthenoiseandconsiderednegligible.ThiscanbeexplainedinthelightoftheresultsdiscussedinSect.3.3,whereweshowedthattheDFEfrompresent-dayBBAissmall(~+5TgC/monthinAugustinBBAX1)forthismodelinthisregionoftheworld.Therefore,alteringtheratioofdiffusefractionreachingthegroundviatheaerosolopticalproperties,thatismodulatingthemagnitudeoftheDFE,doesnothaveameasurableeffectonvegetationproductivity.”

-p20,l24andp21,l1:“do”->“does”.

corrected

-p23,l18:“quantity”->“quantify”.

corrected

-p37,Fig1caption:lookslikea“(reference)”fortheEDMIprojectismissing.

I’veremovedthat‘(reference)’fromthelegend.EMDIdataareaccessibleonline.Thelinktothedatasetisprovidedinthemainmanuscript(P14,line13)andinthedataavailabilitysection.

-p44,Fig8captionreferstosomemissingdashedlines.

Figurecorrected.AlsochangedtheaxislabelsonFig.8forimprovedclarity.Notethatfigure8bisplottedagainstthetotalAOT.ThisisnowmentionedmoreclearlyinthetextP20,lines0-5.

References:

Bellouin,N.,etal.(2013),ImpactofthemodalaerosolschemeGLOMAP-modeonaerosolforcingintheHadleyCentreGlobalEnvironmentalModel,Atmos.Chem.Phys.,13,3027–3044.

vanderWerf,G.R.,etal.(2010),Globalfireemissionsandthecontributionofde-forestation,savanna,forest,agricultural,andpeatfires(1997–2009),Atmos.Chem.Phys.,10,11707–11735.

AnonymousReferee#2

Receivedandpublished:19November2018

ThisstudyexplorestheimpactsofbiomassburningaerosolsonforestproductioninAmazon,takingintoaccountbothdiffusefertilizationeffectsandtheclimaticfeedbackoffireaerosols.Resultsshowthatthebenefitofincreaseddiffuseradiationisnearlyoffsetbythereducedtotalradiation,whileclimaticeffectsoffireaerosolsmakethedominantandpositivecontributionstotheregionalcarbonuptake.Thisisaninterestingandcomprehensivestudy,providingnewperspectivesforbiosphere-pollutioninteractions.Theauthorsperformedconsiderableamountofsensitivityexperimentstoisolateindividualfactorsandtoquantifyassociateduncertainties.HereIhaveonlysomeminorcomments.

Page2,Line23:NotsureSpracklenetal.(2012)providesresultsoffires.AbetterreferenceisRanderson,J.T.,etal.,Theimpactofborealforestfireonclimatewarming,Science,314(5802),1130-1132,2016.

Goodpoint,Sprackenetal.2012wasaboutanalysingthewatercontentofairmassesthatexperiencedvegetatedareaalongtransport.WewerethinkingofmorerecentworkfromD.Spracken’sgrouphoweverthisisnotthemostsuitablereferencetosupportthepointmadeinthissentence.WeusedZempetal.(2017)insteadofRandersonetal(2016)asthefocusismoreontropicalforests.

• Zemp,D.C.etal.:Self-amplifiedAmazonforestlossduetovegetation–atmospherefeedbacks.Nat.Commun.8,14681doi:10.1038/ncomms14681(2017).

Page2,Line32:“tociteafew”whatdoesthismean?

Rephrased:

“AssessingtheoverallimpactofAmazonianforestfiresonecosystemsischallengingasitencompassesacombinationofdirectlosses,andindirectimpactsfromthefireby-productswhichcandependonintricateinteractionsamongseveralearthsystemcomponents,including:thebiosphere,atmosphericcomposition,radiationandenergybudget,cloudsandthewatercycle(Bonan2008).”

Page3,Line21:“didnotaccounted”shouldbe“account”

Corrected.

Page4,Line1:“onlytwostudies”.Notcorrect.Forexample,Yueetal.(2017b)alsousedafullycoupledESMtoquantifyaerosolclimaticandradiativeeffectsonecosystem.It’sbettertosay“limitedstudies”.

Agreethat’sbetterwording.Asaconsequence,thenextsentencehasbeenmodifiedtotakeintoaccountYuanetal.(2007b)findings:

“OnlyalimitednumberofstudieshaveconsideredtheDFEwithinafullycoupledearthsystemframework(e.g.StradaandUnger,2016;Ungeretal.,2017,Yueetal.,2017busingtheNASAGISSModelE2–YIBs)toinvestigatetheroleofaerosolsandhazeonvegetation.AlthoughthesestudieshaveinvestigatedtheroleofdiffuseradiationonGPPandisopreneemissions(StradaandUnger,2016;Ungeretal.,2017),understandingoftheindirectimpactofclimateeffectsfromaerosolsonvegetationproductivityremainsveryuncertain.ThiswasaddressedoverChinabyYueetal.(2007b)whodemonstratedthataerosolinducedhydroclimaticfeedbackscanpromoteecosystemNPP.”

Page6,Line11:“Thephotosynthesismodelisbasedupontheobservedprocesses”,whatkindofprocesses?Moredetails.

Addedtheprocessesinthesentence.NotethatfulldescriptionoftheseareprovidedbyCollatzetal.(1991,1992)whichisreferencedattheendofthisparagraph:

“Thephotosynthesismodelisbasedupontheobservedprocessesofgasandenergyexchangeattheleafscale,whicharethenscaleduptorepresentthecanopy.Ittakesintoaccountvariationsindirectanddiffuseradiationonsunlitandshadedcanopyphotosynthesisateachcanopylayer.Inthisway,photosynthesisofsunlitandshadedleavesiscalculatedseparatelyundertheassumptionthatshadedleavesreceiveonlydiffuselightandsunlitleavesreceivebothdiffuseanddirectradiation(Daietal.,2004;Clarketal.,2011).Leaf-levelphotosynthesisiscalculatedusingthebiochemistryofC3andC4photosynthesisfromCollatzetal.(1991)andCollatzetal.(1992).”

Page6,Line28:“thetropicalFrenchGuyanasite”.Itmightbeinadequatetocalibratemodelparametersusingdatafromasinglesite.

Wetotallyagree.Unfortunately,goodqualityobservationsthatincludemeasurementoftotalanddiffuselightinadditiontocarbonfluxesintheAmazonarerare.Notethatthisexercise(modellingoftheFrenchGuyanasite)isnotforvalidationpurposesbutforexploringJULESsensitivitytoparametersusingrealisticforcing.EvaluationofGPP/NPPisprovidedbycomparingHadGEM2againstMODISandFLUXCOMintheresultsection.

Page8,Line3:“30-years”shouldbe“30-year”

Modified30-yearsto30yearstobeconsistentwithotherpartofthetext.Page17,Line5:“Fig5d”shouldbe“Fig4d”,thenextlineshouldbe“Figs4a,b,c”.

Wellspotted.AlsocorrectedonPage16,Line32.Page21,Line28:“fertilisation”,it’sbettertouse“fertilization”tobeconsistentwithpreviousinstances.

Goodpointaboutconsistency.ACPacceptsallstandardvarietiesofEnglishinordertoretaintheauthor’svoice.However,thevarietyshouldbeconsistentwithineacharticle.BecausewehaveusedBritishEnglishintherestofthemanuscript,wehavereplacedoccurrencesofFertilizationwithFertilisation.

Figure2:JASshouldbeJuly-August-SeptemberCorrected.

Figure7:IsthatpossibletocalculatethesensitivityofdNPPtoBBA,andtocomparethevaluesamongdifferentmonths?Theseresultscantellustheimpactsofvariantenvironmental/climaticconditionsonfireaerosol-inducedNPPperturbations.

I’mnotsurethatweunderstandwhatissuggested.DoyousuggestcalculatingNPPsusceptibilitytoBBA(e.g.dln(NPP)/dln(BBA_emissions))?

NotethatthevastmajorityofBBAemissionsovertheAmazonoccurduringthedryseason(peakinginAugustandSeptember)soitisverylikelythatwewouldnotbeabletoderiveaclearsignaloutsidethatperiod.