A Quick Report on a Dynamical Downscaling Simulation over China Using the Nested Model
A Quick Report on a Dynamical Downscaling Simulation over China Using
the Nested Model
ATMOSPHERICANDOCEANICSCIENCELETTERS,2010,VOL.3,NO.6,325—329
AQuickReportonaDynamicalDownscalingSimulationoverChinaUsing theNestedModel
YUEn—Tao,,WANGHui.Jun,andSUNJian.Qi
1
.
Nansen—
ZhuInternationalResearchCentre,InstituteofAtmosphericPhysics.ChineseAcademyofSciences.Beijing100029,China
ClimateChangeResearchCenter,ChineseAcademyofSciences,Bei]ing100029,China GraduateUniversityoftheChineseAcademyofSciences,Beijing100049,China Received15October2010;revised8November2010;accepted8November2010;published16November2010
AbstractThisPaperdescribesadynamicaldownscaling
simulationoverChinausingthenestedmode1system.
whichconsistsof坊emoditied舱atherResearchand
ForecastingModel(WRY)nestedwiththeNCARCom—
munityAtmosphereModelrCAM).Resultsshowthat
dynamica1downscalingisofgreatvalueinimprovingthe
mode1simulationofregionalclimaticcharacteristics.
WRFsimulatesregionaldetailedtemperaturefeatures
betterthanCAM.Withthespatialcorrelationcoemcient
betweentheobservationandthesimulationincreasing
from0.54forCAMto0.79forWRF,theimprovementin precipitationsimulationismoreperceptiblewithWRF Furthermore.theWRFsimulationcorrectsthespatialbias oftheprecipitationintheCAMsimulation.
Keywords:dynamicaldownscaling.WRF.CAM
Citation:Yu,E..T.H.一J.Wang,andJ.-Q.Sun,2010:A
quickreportonadynamicaldownscalingsimulationover Chinausingthenestedmode1.Atmos.Oceanic&f.Lett.. 3,325-329.
1IntrOductiOn
Duetocoarseresolution.theperformanceofglobal circulationmodelsfGCMs)is1imitedinsimulatingre—
giona1climatevariability,especiallyforcomplexterrain. Therefore.statistica1anddynamicalmethodshavebeen developedtoimproveregionalclimatesimulations.Dy. namicaldownscaling.animportantdynamicalmethod (Castroeta1.,2005;Murphy,1999),istheapproachin whichregionalclimatemodels(RCMs,areforcedby lateralboundaryconditionsfromGCMorglobaldata reanalysisatregulartimeintervals.BecausetheRCMs usefinersurfaceparametersandmorecomplicated parameterizationschemes,dynamicaldownscalingcan significantlyimprovethesimulationabilityforregiona1 climatesovervariousareasoftheworld(DeSalesand Xue,2006;Dickinsoneta1.,1989;FennessyandShukla. 2000;GiorgiandMearns,1991:Joneseta1.,1995,l997; Misraetal一2003:WalshandMcGregor,l995).OverEast Asia.dynamicaldownscalingalsoshowspredominance comparedtoGCMsimulations(Fu2003:Gaoeta1.. 2002,2008;JuandWan2006;Jueta1.,2007;Parketa1.,
2008;Waneta1.2003).
Althoughmostpreviousdynamicaldownscalingstud. Correspondingauthor:YUEn-Tap,yetsyu@mail.iap.ac.ca iesoverChinautilizeRegCM.weusetheWeatherRe—
searchandForecastingModel(WRF,.TheWRFwasini. tiallydevelopedandtestedforsimulationandforecasting ofweather,ithasrecentlybeenadaptedtosimulatecli. mate.ThisWRFmodelhasbeenusedforshort.termre. gionalclimatevariability(Loeta1.,2008;Qianeta1., 2010,:however,theperformanceoftheWRFasady. namicaldownscalingmethodinlong—termsimulations
overChinaremainstobedetermined.Toaddressthisis. sue,wedevelopedanewnestedclimatemodelandevalu. ateditssimulations.
2Modelsanddata
2.1Atmosphericglobalcirculationmodel
TheGCMmodelusedinthisstudyisthecoupled
CommunityAtmosphereModelversion3(CAM3)一
CommunityLandModelversion3(CLM3)model
(Collinseta1.,2004;Olesoneta1.,2004),whichconsists oftheCAM3andCLM3.ForCAM,weemploythefinite volumedynamicalcorewithahorizonta1resolutionof2. latitudeby2.5.longitudeand26levelsinthevertical direction.CLMhas10unevenlyspacedverticalsoillay—
ers.uptofivesnow1ayers,andonevegetationlayer.The CAMsimulationconsistsofAtmosphericModdInter—
comparisonProject(AMIP)-typeintegrations(Phillips, 1996)forcedbyobservedglobalSSTs.Theintegration periodisfrom1September1977to31December2002 withoutputintervalofsixhours.Theflrstfouryears
(1977—80)areconsideredasthespin.upperiod,andthe outputoftheremainingyearsisusedasthelateralbound—
aryconditionsfortheWRFmode1.
2.2Regionalclimatemodel
Theregiona1climatemode1isWRFversion3.2.and theintegrationdomaincoversallofmainlandChina;the integrationdomainhas120gridsalongtheEast—West
directionand90gridsalongtheNorth—Southdirection,
withthecenterat35.N,105.E(Fig.1).Weused60km gridspacingand31sigmalevelswimthemode1topat50 hPa.TheparameterizationoptionsselectedfortheWRF simulationincludetheWRFSingle.Moment6classmi. crophysicsscheme.RapidRadiationTrant;ferModel (RRTM1long.waveradiationscheme,Dudhiashort-wave radiationscheme,theuntiedNoahland.surfacemodel, andtheYonseiUniversityboundarylayerscheme.Initial 326ATMOSPHERICANDoCEANICSCIENCELETTERS 50.N
40oN
30.N
20N
50.N
Figure1Domainandtopography(meters)formodelsimulationand subregionsfordetailanalysisContourintervalsare400iYl,andvalues
greaterthan1000mareshaded40.N
conditionsandlatera1boundaryconditionsareallfrom CAMoutput.SSTdata.deepsoi1temperatureandgreen fractiondatawereupdatedeverysixhours.Thesimula—
tionperiodisfrom1981to2002,withthefirsttwoyears
(1981-82)asthespin—upperiod,andthefollowingresult
isusedforcomparison.
2.3observatiOnaldata
30.N
20.N
Thetemperaturedatausedformodelvalidationisthe50.N griddeddailytemperaturedataoftheChinaMeteorologi—
calAdministration(cn05)at0.5.×0.5.resolution,The
cn05dataisconstructedfromtheinterpolationof75140.N observingstationsinChinaovertheperiodof196l一2005
(Xueta1..2009).TheprecipitationdataisfromtheXie EastAsiadailygriddedrainfalldataat0.5.×0.5.resolu—
tion;thisprecipitationdataisconstructedoverEastAsia from1978to2003usinggaugeobservationsatover2200 stationscollectedfromseveralindividualsourcesfXieet a1..2007).
3Results
Thevalidationandcomparisonofthetwomodelre—
sultsarebasedontheobservations.Giventhedifferent horizontalresolution,weinterpolatedthemodelfields ontothesamegridsasthecn05dataforcomparison. 3.1Temperature
Figure2showstheannua1meantemperaturefronlob—
servationandmode1simulations.TheobservationsfFig. 2a)indicatehighertemperaturesoverSouthChinaand 1owertemperaturesovertheTibetanPlateauandnorthern China.Ingeneral,thetemperaturegraduallydecreases northwardandwestward.Oneexceptionisinthe11a"m BasinandJunggarBasin.wherethetemperatureisrela—
tivelyhigherduemainlytothehighalbedoofthedeserts
intheseregions.
TheCAMandWRFcanbothcalclturethelarge.scale characterjsticsoftemperatureoverChina(Fig.21.The 30.N
20.N
V0L_3
90.El2O.E
一
9—6—30369l2l5I821
Figure2The20一yearannualmeantemperature(.C)of(a)thecn05 data,(b)theCAMsimulation(Correlation:0.937;RMSE:2992),and fc1thesimulationoftheWRFforcebyCAMoutput(Correlation:0.96; RMSE:2.857)
spatialcorrelationcoefficientsbetweenobservationsand simulationsare0.94forCAMand0.96forWRF.Dueto finerresolution.theWRFcanreproducedetailedlocal featuresofChinesetemperaturedistribution,especiallyin theTibetanPlateau,SichuanBasin,andNortheastChina. Forthesimulatedtemperaturevalues.WRFalsopresents betterperformance,showinglesstemperaturebiasas comparedtotheCAMsimulation.
3.2Precipitation
TheWRFsimulatesprecipitationmuchbetterthan N0.6YUETAL.:DYNAMICALDOWNSCALINGSIMULAr10NOVERCHINA CAM.AsshowninFig.3.WRFcanmoreaccuratelyre—
producetheobservedprecipitationdistributionfeatures; maximumprecipitationmainlyOccursoverSouthChina, andtheprecipitationdecreasesnorthwestward.withthe minimumvalueoverNorthwestChina,particularlyover theTarimBasin(Fig.3a).Conversely,theCAMsimulates
themaximumprecipitationoverCentralChina,which disagreeswiththeobservations.Thespatialcorrelation coe艏cientsbetweentheobservationsandsimulationsare 0.54forCAMand0.79forWRF.Valuecomparison
90oEl20.E
25501002505007501000125015002000
Figure3The20一yearannualmeanprecipitation(mm)of(a)theXie data,fb)theCAMsimulation(Correlation:0.542;RMSE:1.403mm d),and(c)thesimulationoftheWRFforcebyCAMoutput(Correla- tion:0.791:RMSE:O.9831Tund,.
327
showsthatthesimulatedbiasoftheWRFismuchless thanthatoftheCAM(Fig.3.
TheabovecomparisonsshowtheWRFtobesuperior toCAMandthatdynamicaldownscalingisofvaluein regionalclimatesimulation.
Itiswel1knownthatthe
precipitationisquitepoor;
abilityofGCMstosimulate
However,thenested—model
dynamicaldownscalingmethodcanimprovethemodel simulationofprecipitation.Toinvestigatethesimulation ofthetemporalfeatureofprecipitation,thetimeseriesof annualmeanprecipitationaveragedoverallthesub..re.. gionswithinMainlandChinaarecalculated(Fig.4,.In general,theimprovementissignificantoveralmostall sub—regions.AsshowninFig.4,theWRFsimulatedpre—
cipitationvaluesareclosertotheobservationsforalmost everyyea5especiallyinNortheastChina.theeasternarid region,NorthChinaandthe
regions,wheretheRMSEs
Northwestaridandsemiarid
fortheCAM(WRF)were
0.57(0.24),1.43(0.32),1.32(0.46),and0.57r0.161mm d,.respectively.Forothersub—regions.suchasSouth
ChinaandtheTibetanPlateau,theamountofprecipitation simulatedbyWRFisbetweenobservedvaluesandthe CAMvalues;theseresultsindicatethattheWRFcanim—
provethesimulationofprecipitationintheseareas. 4Summary
Inthisstudy,thenewnestedmode1isdevelopedusing theWRFandtheCAM.Comparisonbetweentheobser—
vationsandmodelsimulationsshowsthattheWRFcan improvetheabilityofregionalclimatesimulation.The regionaldetailsoftemperatureproducedbytheWRFare muchbetterthanthoseproducedbytheCAM.Theim—
provementofprecipitationsimulationismoreapparent thantemperature;thespatialcorrelationtoefficientin—
creasesfrom0.54fortheCAMto0.79fortheWRF.and thedisplacementofprecipitationcellscanbecorrectedin theWRFsimulation.OverdifferentsubregionsofChina, theWRFalsoshowsimprovementovertheCAM.
Inanattempttoinvestigatethedynamicaldownscaling abilityoftheWRFnestedwiththeCAM.thispaperad—
dressedseveralissues.TheWRFcanreducetheRMSEof precipitationoverChina.butitshows1ittleabilityin simulatingtheinter—annua1variationofprecipitationiust asCAMdoes.Thisweaknessisbecausetheinter—annual
variationsimulatedbytheWRFisdrivenbytheboundary conditionsthatareexclusivelyfromtheCAMmode1.An
importantremainingissueistoillustratehowwellthe nestedmodelsystemcanrepresentthesummermonsoon systemofChina.Furtheranalysisofthesimulationofthe summermonsoonsystemshouldbeconductedinthefu—
ture.
Acknowledgements.ThisresearchwassupportedbytheSpecial FundforPublicWelfareIndustry(meteorology)(GrantNo. GYHY200906018),theNationa1BasicResearchProgramofChina (973Program)fGrantNo.2009CB421406).andtheNationalNatu—
ralScienceFoundationofChinafGrantNos.40875048and 40821092).
328
NortheastC'hina
ATM0SPHERICANDoCEANICSCIENCELETTERS
NorthChina
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1984l988l992l9962000
TibetanPlateau
3.O
2.5
2.O
15
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O5
O
42
39
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33
30
2.7
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Easternaridregion
CentfalChina
Northwestaridandsemi-aridregion
l984l988l992l9962000
19841988l992l9962000
Observation—O—CAM-?一CAM.WRF
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