SpatialfeaturesofrainfrequencychangeYanfenLinetal - PDF document

1 ACPD 10,14495–14511,2010 Spatialfea
ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| Abstract Aspatial-temporalanalysishasbeenconductedusingsatelliteobserveddistributions ofrainfrequency,NO2concentrationandaerosol,withfocusonthespringseason.As revealedbymeasurementsfrom1998–2009overShanghai,China,thesuppressionof rainismainlyattributedtothereductionofrainoccurrenceratherthanchangesinrain 5 intensity.Theoverallfeaturesemergefromtheregion-by-regionanalysesthatthere isaninverserelationshipbetweentherainfrequencyandthepollutionandassociated aerosolsatcontinentalscaleinspring.Theenhancementofpollution-producedCCN inadditiontomineraldustfromlong-termtransportsuppressestherainfrequ

2 ency,as favoredbytopography,wind,andothe
ency,as favoredbytopography,wind,andothermeteorologicalconditions. 10 1 Introduction Human-inducedclimatechangehascausedaredistributionofprecipitation(Zhang etal.,2007).Besidesthegreenhousegases-inducedglobalwarming,anthropogenic aerosolsincreaseconcentrationsofcloudcondensationnuclei(CCN)andice-forming nuclei(IN),whichalterthemainpathofprecipitation-formingmicrophysicalprocesses 15 andtheprecipitationamount(e.g.,CottonandPielke,1995;Lohmannetal.,2005; Rosenfeldetal.,2008).Theresponseofthehydrologicalcycletotheaerosolindi- recteectisdierenttothegreenhouseeect,andthehydrologicalcycleisexpected tobeweakenedduetoaerosoleects(Ramanathanetal.,2001;IPCC,2007).The inuencesofanthropogenicpollutantsonprecipitationareconfoundedbydynamicpro- 20 cessesinvarioustemporalandspatialscales,whichheightentheneedforaccurate informationabouttemporalandspatialvariationsinprecipitation

3 andaerosols(IPCC, 2007;Newetal.,2001;Yan
andaerosols(IPCC, 2007;Newetal.,2001;Yangetal.,2004;Qianetal.,2009).Few,ifany,studieshave reporteddirectlyobservationallinkagebetweentherainfrequencyandthepollution andassociatedaerosolsatcontinentalscale. 25 Heterogeneousspatialdistributionofanthropogenicaerosols,whichresultsfrom 14496 ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| 2009areusedinthisstudy.Asamarkerofairpollution,troposphericnitrogendioxide (NO2)hasbeenmonitoredbyboththeGlobalOzoneMonitoringExperiment(GOME) andSCanningImagingAbsorptionSpectroMeterforAtmosphericCHartographY (SCIAMACHY)satellites.Hence,monthlyNO2verticalcolumnconcentrationfrom combinedGOME(1998–2002)andSCIA

4 MACHY(2003–2009)measurements(Richte
MACHY(2003–2009)measurements(Richter 5 etal.,2002;source: http://www.iup.uni-bremen.de/doas/data products.htm )areused toquantifyairpollutionchangesoverthesameperiodofPRdataset.Precipitation canbeinuencedbyanthropogenicaerosolsassociatedwithpollutionthroughtheir rolesincloudcondensationnucleiandicenuclei.Toassessthechangesofaerosol loadingintheatmospheredirectly,aerosolopticaldepthsfromMODerateresolution 10 ImagingSpectroradiometer(MODIS)onboardtheTerraSatellite(Kingetal.,2003) arealsoused.Inadditiontotheabovethreecombinedsatellitedatasetsthatprovide thespatial-temporalvariationofpollution,aerosols,andprecipitation,thesurfacerain gaugeprecipitationdataareusedtoverifythesatellitemeasurementsandinvestigate therelationshipbetweenprecipitationandairpollutants. 15 3 Results DuetotherelativelyshortlifetimeofNO2andtheverticaldistributionofNOxsources, NO2columnsobservedfromspacearedomi

5 natedbytheNO2concentrationinthe boundary
natedbytheNO2concentrationinthe boundarylayerandatthelocation(Richteretal.,2005).AsshowninFig.1,satellite retrievedNO2columnconcentrationinspringatShanghaiincreasedsubstantiallyfrom 20 1998to2009.ThelineartrendinNO2columnconcentrationis1.91015molec/cm2 peryear.Withrespecttothereferencevalueof6.01015molec/cm2inspring1998, airpollutioninShanghaiwastripledfrom1998to2009.Nitrogendioxideisaneective absorberofvisibleandnear-ultravioletsolarradiation.Atwavelengthsbelow400nm, photodissociationofNO2generatesNOandOatomsthatquicklyattachtomolecular 25 oxygentoformozone.Back-reactionsofNOwithozoneand/orotherradicalsestablish asteadystatebetweenNOandNO2inthetroposphere.ThephotodissociationofNO2 14498 ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc

6 Printer-friendlyVersion InteractiveDisc
Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| toevaluatetheseasonalrainfrequencyat11grids,denedastheratioofraining pixelstototalsamplingpixels.Usingsucharelativeparameteralsominimizesthesys- temicbiasandretrievaluncertaintiesofPRrainrateretrievals.Clearly,thedecrease trendof4.04%peryearinrainfrequency(0.21%peryearinabsoluterainfrequency) isslightlygreaterthatthedecreasetrendof2.49%peryearinrainamount(5.75mm 5 peryearinabsoluterainamount).Itsuggeststhatreductioninprecipitationismainly duetothesuppressionofrainoccurrencewithaslightenhancementofrainintensity. Cloudformationisstronglycontrolledbymeteorologicalconditions,suchastemper- atureandatmosphericconvection.TheincreasedNO2andaerosols(sootparticles inparticular)aecttheradiativeprocessesintheatmospherethroughenhancingab- 10 sorptionofsolarradiationa

7 ndheattheatmosphere,whichleadtochangesin
ndheattheatmosphere,whichleadtochangesintheair temperatureandatmosphericstability(Ramanathanetal.,2005).Iftheatmosphere becomesmorestable,theupwardmotionsaredepressed,andcloudformationisre- duced,resultinginreductionofprecipitation(Zhaoetal.,2006).Furthermore,ifthe moistureintheatmosphereisnotalteredbytheincreaseinpollutionparticlenumber 15 concentration,theclouddropletradiuswilldecrease,resultinginadecreaseinthe precipitationeciency(IPCC,2007;Ramanathanetal.,2001).Theoppositetrends ofprecipitationandairpollutantsimplythepossibilitythattheincreasedparticlesover urbanareassuppressthelocalprecipitation,particularlytherainfrequency. TheinverserelationsofrainfrequencyandprecipitationtotheconcentrationsofNO2 20 andaerosolsatasinglesiteforpastdecadescanbecasual,asprecipitationchanges arestronglyinuencedbychangesoflargescaledynamics.Toexcludethepossi- bleinuenceofmeteorologicalfac

8 torchangesonspecicsites,thespatial-t
torchangesonspecicsites,thespatial-temporal distributionofrainfrequency,NO2concentration,andaerosolloadingareinvestigated. ManystudiessuggestedthattherewerestrongincreasetrendsofNO2insome 25 regionsofChinaandIndiaforthepastdecade(Richteretal.,2005;andvanderAet al.,2006).AsillustratedinFig.2a–c,thoseregionsincludetheNorthChinesePlain, YangtzeRiverDelta,PearlRiverDelta,SichuanBasinandIndiaGangesregionwhere economyhasbeendevelopedsubstantiallyinrecentyears.SinceAsiamonsoonisin 14500 ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| increasedsubstantiallyoverthepastdecade,accompaniedbyanincreaseofthene modeAOD.IntheYangtzeRiverrainfrequ

9 encyreductionband,therearemanymega- citi
encyreductionband,therearemanymega- cities,suchasShanghai,Nanjing,Wuhan,andChangsha.Forthepastdecadethe economicdevelopmentresultedinseverepollutionasindicatedbytheincreasetrends inNO2concentrationandinthenemodeAOD.Thespatialcorrelationbetweenthe 5 increasetrendofNO2concentrations(andthepositivenemodeAODtrend)andthe decreasetrendofrainfrequencysuggeststhatthetwohavesomefundamentallinkage. TheIndia-MyanmarRegionislocatedtothesouthofHengduanMountain.Moisture airmassfromtheIndianOceanwillformorographicprecipitation,whichcontributes tothehighrainfrequencyintheregion.AlthoughthetrendinNO2concentrationwas 10 notsignicantintheregion,theenhancementofthecoarsemodeAOD(andNO2 concentration)intheupwindregionwasclearlyevident.Theobserveddecreasetrend inrainfrequencyalongHengduanMountainreectstheimpactsofenhancedaerosols ontheorographicprecipitation(GivityandRosenfeld,2004;Rosenfeldet

10 al.,2007). Intheupwindregion,thedecrease
al.,2007). Intheupwindregion,thedecreasetrendofrainfrequencycoincidedwellwiththe 15 increasetrendincoarsemodeAOD. TheonlyregionwithanincreaseprecipitationfrequencyislocatedattheNepal- Indiaregion,borderedbytheHimalayamountainrangetothenorth.Asdiscussed previously,bothneandcoarsemodeAODsshowedanegativetrendintheregion. Thusthereisaninverserelationshipbetweentherainfrequencyincreaseandthe 20 aerosolreduction,whichisconsistentwithourhypothesisthataerosolsplayakeyrole ofmodulatingrainfrequency. However,changesinlarge-scaleatmosphericcirculationcouldresultinobserved changesinprecipitation.Thelarge-scalefactorsthatcorrelatewellwithprecipita- tionarethecolumnprecipitablewater(PW)anddivergenceofwatervaportransport 25 (DWVT)intheatmosphere(Parketal.,2007;Qianetal.,2009).WeusedNCEPre- analysisdatatoinvestigatetrendsofthetwofactorsintheselectedregions.Although theresolutionofNCEPreanalysisdata

11 iscoarseat2.52.5,theregion
iscoarseat2.52.5,theregionalfeatures areevident.AsshowninFig.3,thespatialdistributionofthePWinspringshows 14502 ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| therapidurbanizationandmotorization.Wespeculatethat1)theincreasedNO2and aerosols(sootparticlesinparticular)enhancetheabsorptionofsolarradiationand stabilizetheatmosphere,resultinginreductionofcloudformationandrainfrequency; and2)theenhancementofpollution-producedCCNinadditiontomineraldustfrom long-termtransportfurthersuppressestherainfrequency,asfavoredbytopography, 5 wind,andothermeteorologicalconditions.Certainly,morerobuststatisticalstudyand detailedmodelinginvestigatio

12 narewarrantedtofurtherunderstandtheobser
narewarrantedtofurtherunderstandtheobservedrela- tionshipbetweentherainfrequencyandthepollutionandassociatedaerosols. Asthelarge-scaleprecipitationiscontrolledbyevaporation,aerosolsmightinu- enceitbysurfacecooling.Inparticular,aerosolmicrophysicaleectscanactually 10 aectprecipitationcharacteristics.RecentstudiesinNorthAmericaalsoshowedthat therainfrequencywasincreased(Karletal.,1998)whilethetroposphericNO2col- umnwasdecreased(Richteretal.,2005).Itfurthercorroboratesthehypothesisthat thehighconcentrationofanthropogenicemissionofaerosolanditsprecursorgases suppressesrainoccurrence.Furthermore,thesuppressionofprecipitationleadsto 15 anincreaseinmoistureandhygroscopicparticlesintheatmosphere.Theincreased amountofmoistureandhygroscopicparticlesenhancesregionalhazeifthemoistureis relativelylimited,orresultsinintenseprecipitationifwatervaporintheatmosphereex- ceedsathreshold.This

13 hypothesisissupportedbythesurfaceobserva
hypothesisissupportedbythesurfaceobservationsinChina, i.e.,increasinghazedays(Zhuangetal.,2007);andanincreasingtrendofintensive 20 precipitationfrequencyovertheYangtzeRiverBasin(Jiangetal.,2007;Suetal., 2007). Thesendingshighlightthethreattovitalwaterresourcesinpollutedregionsofthe world,asinsomeindustrializedareasofChinaandIndia,notonlylocallybutalsoin thedownwindregions.Theimportanceofthatisunderlinedbytherealizationthatitis 25 nothightemperaturesduetoglobalwarmingbutratherthelackofwaterthatmakes aregionintoanunlivableland.Particularly,anyprecipitationchangeinspringwill signicantlyimpactthestablecropproductionintheregions. 14504 ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|Discu

14 ssionPaper|DiscussionPaper|DiscussionPap
ssionPaper|DiscussionPaper|DiscussionPaper| Rosenfeld,D.,Dai,J.,Yu,X.,Yao,Z.,Xu,X.,Yang,X.,andDu,C.:InverseRelationsBe- tweenAmountsofAirPollutionandOrographicPrecipitation,Science,315(5817),1396– 1398,doi:10.1126/science.1137949,2007. Rosenfeld,D.,Lohmann,U.,Raga,G.B.,O'Dowd,C.D.,Kulmala,M.,Fuzzi,S.,Reissell, A.,andAndreae,M.O.:FloodorDrought:HowDoAerosolsAectPrecipitation,Science, 5 321(1309),1309–1313,doi:10.1126/science.1160606,2008. Singh,R.P.,Prasad,A.K.,Chauhan,S.S.,Singh,S.,andHolben,B.,Long-rangetransportof aerosolsandtheirimpactontheairqualityoftheIndo-Gangeticbasin,36thCOSPARScien- ticAssembly,held16–23July2006,inBeijing,China,MeetingabstractfromtheCDROM, #1343,2006. 10 Su,B.,Jiang,T.,Ren,G.,andChen,Z.:TrendsofExtremePrecipitationovertheYangtzeRiver BasinofChinain1960–2004,Adv.ClimateChangeRes.,3(Suppl.),45–50,2007. Sun,Y.,Zhuang,G.,Wang,Y.,Z

15 hao,X.,Li,J.,Wang,Z.,andAn,Z.:Chemicalco
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16 au,K.M.:TrendAndVariabilityOfChinaPrecip
au,K.M.:TrendAndVariabilityOfChinaPrecipitationInSpringAndSummer: LinkageToSea-SurfaceTemperatures,Int.J.Climatol.,24,1625–1644,2004. Zhai,P.,Zhang,X.,Wan,H.,andPan,X.:TrendsinTotalPrecipitationandFrequencyofDaily PrecipitationExtremesoverChina,J.Climate,18(7),1096–1108,doi:10.1175/JCLI-3318.1, 2005. 30 Zhang,X.,Zwiers,F.W.,Heger,G.C.,Lambert,F.H.,Gillett,N.P.,Solomon,S.,Stott,P. A.,andNozawa,T.:Detectionofhumaninuenceontwentieth-centuryprecipitationtrends, Nature,448,461–466,doi:10.1038/nature06025,2007. 14507 ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| Fig.1.(a)TimeseriesofMODISaerosolopticaldepthandsatellitemeasuredtr

17 oposphericNO2;(b)timeseriesofTRMMPRrainf
oposphericNO2;(b)timeseriesofTRMMPRrainfrequencyandrainamount,andsurfaceraingaugemeasuredprecipitationfrom1998to2009forthe11gridnearShanghai. 14509 ACPD 10,14495–14511,2010 SpatialfeaturesofrainfrequencychangeYanfenLinetal. TitlePage Abstract Introduction Conclusions References Tables Figures J I J I Back Close FullScreen/Esc Printer-friendlyVersion InteractiveDiscussion DiscussionPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| Fig.2.Spatialdistributionsinspringduring1998–2009:(a)meantroposphericNO2columndensity,(b)troposphericNO2columndensityannualtrend,(c)troposphericNO2columnden-sityannualtrendwithsignicantlevelabove95%,(d)MODISmeantotalAerosolOpticalDepth(AOD),(e)MODISnemodeAODannualtrend,(f)MODIScoarsemodeAODannualtrend,(g)meanTRMMPRrainfrequency,(h)TRMMPRrainfrequencyannualtrend,and(i)TRMMPRrainfrequencyannualtrendwithsignicantlevelabove9