Tropicalexpansiondrivenbypolewardadvancingsubtropicalfront
HuYang1,Gerrit Lohmann1,JianLu2,EvanJ.Gowan1,Xiaoxu Shi1,Jiping Liu3,Qiang Wang1
1. AlfredWegenerInstitute,HelmholtzCentreforPolarandMarineResearch,Bremerhaven,Germany2. AtmosphericSciencesandGlobalChangeDivision,PacificNorthwestNationalLaboratory,Richland,Washington,USA
3. DepartmentofAtmosphericandEnvironmentalSciencesUniversityatAlbany,StateUniversityofNewYork,Washington,USA
07.May.2020 1
https://www.joboneforhumanity.org/the_mystery_of_the_expanding_tropics
Tropospheric temperature trends for 1979 to 2005 based on satellite-borne MSU observations. Fu. et al. (2006)
o StormtracksYin,(2005)o JetStreamsArcherandCaldeira,(2008)o WesterlywindsChenetal,(2008)o PrecipitationpatternScheff
andFrierson,(2012)
o CouldNorrisetal,(2016)o Large-scaleoceangyres
Yangetal,(2020)
2
Previousmechanisms
• IncreasingGHG
• DecreasingozoneoverAntarctic
• IncreasingaerosoloverNorthernHemisphere
• Naturalvariations(PDO) Staten et al., 2018
3
MajorGaps• NoobservationalsupportshowingthatGHG,ozone,aerosolcorrelatewiththevariationsoftropicalwidth (Allen&Kovilakam,2017).
• Thesubtropicalclimatezoneshiftedduringpastglacial-interglacialcycles,withoutevidenceofchangesinozoneoraerosol (Gersonde etal.,2005;Toggweiler &Russell,2008;Bard&Rickaby,2009;Benzetal.,2016)
• GHGalone(withoutcontributionfromSST)playsaminorroleinwideningtropics (Grise&Polvani,2014)
4
Yangetal,(2020)
Polewardshiftofthemajoroceangyres
detectedinawarmingclimate
Whetheroceanplayacrucialrolein
expandingtropics?
5
Data andMethod
Ø Observations(ERA5,HadISST,NOAA-OISST)
ØCMIP5multi-model(24)simulations(piControl,1pctCO2).
Ø Sensitivitysimulation(FESOM,ECHAM6)
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ModelName InstitutionACCESS1.0 CentreforAustralianWeatherandClimateResearchACCESS1.3 CentreforAustralianWeatherandClimateResearchCanESM2 CanadianCentreforClimateModellingandAnalysisCNRM-CM5 CentreNationaldeRecherchesMeteorologiques/CentreEuropeendeRechercheet
FormationAvanceesenCalculScientifique(CNRM/CERFACS)CNRM-CM5.2 CentreNationaldeRecherchesMeteorologiques/CentreEuropeendeRechercheet
FormationAvanceesenCalculScientifique(CNRM/CERFACS)CSIROMk3.6.0 CommonwealthScientificandIndustrialResearchOrganisation incollaborationwiththe
QueenslandClimateChangeCentreofExcellenceGFDL-CM3 GeophysicalFluidDynamicsLaboratory
GFDL-ESM2G GeophysicalFluidDynamicsLaboratoryGFDL-ESM2M GeophysicalFluidDynamicsLaboratoryGISS-E2-H NASAGoddardInstituteforSpaceStudiesGISS-E2-R NASAGoddardInstituteforSpaceStudies
HadGEM2-ES MetOfficeHadleyCentreINM-CM4 InstituteforNumericalMathematics
IPSL-CM5A-LR Institut PierreSimonLaplaceIPSL-CM5A-MR Institut PierreSimonLaplaceIPSL-CM5B-LR Institut PierreSimonLaplaceMIROC-ESM JapanAgencyforMarine-EarthScienceandTechnology,AtmosphereandOceanResearch
Institute(TheUniversityofTokyo),andNationalInstituteforEnvironmentalStudies
MIROC5 AtmosphereandOceanResearchInstitute(TheUniversityofTokyo),NationalInstituteforEnvironmentalStudies,andJapanAgencyforMarine-EarthScienceandTechnology
MPI-ESM-LR MaxPlanckInstituteforMeteorologyMPI-ESM-MR MaxPlanckInstituteforMeteorologyMPI-ESM-P MaxPlanckInstituteforMeteorologyMRI-CGCM3 MeteorologicalResearchInstituteNorESM1-M NorwegianClimateCentreNorESM1-ME NorwegianClimateCentre
List of CMIP5 models used in our study
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Edgeoftropics: u-windchangesfromeasterlytowesterly(USF)
Individuallyfromfiveoceanbasins
Waugh et al., 2018 8
Yangetal,(2020)Underreview onGRL.
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MeridionalSSTgradientanomaliesassociated withwidertropics.
Definitionofofmeridionalpositionofsubtropicalfronts 10
ClimatologymeridionalSSTgradients
Greyline:meridional positionofsubtropicalfront,Colouredline:edge oftropics.Positivevaluesindicate poleward shift,viceversa.
11Yangetal,(2020) Underreview onGRL
Yangetal,(2020) Underreview onGRL.Eriksen et al., 2014
Subtropicalconvergencezone(SCZ)Regionswithheavyplasticaccumulation
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Fu. et al. (2006)
Yangetal,(2020) Underreview onGRL.13
Aqua-PlanetFESOM
Yangetal,(2020) Underreview onGRL.
SCZ
SCZ
SCZSCZ
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SSTwarmingpatternunderuniform1degreewarmerSATforcing
Yangetal,(2020) Underreview onGRL.
SCZ
SCZ
15
Warmersubtropicalocean(polewardshiftofsubtropicalfront)driveswidertropics
Yangetal,(2020) Underreview onGRL. 16
Yangetal,(2020) Underreview onGRL.17
Answerstothepreviousquestions
ü Theaerosol,especiallyforblackcarbon,contributetowarming overthemid-latitudes (Allenetal.,2012),whichhasthepotentialtosustainapolewardshiftofatmosphericsubtropicalfront.
ü TheozoneholeovertheAntarcticcools the Antarctic(Randel&Wu,1999; Thompsonetal.,2011;Orretal.,2012)contributingtothemigrationofthemid-latitudetemperaturegradients.
ü Thetropicsarenarrowerduring glacialperiod(Sonetal.,2018),becausehigh-latitudecoldwaterexpandstowardslowerlatitudes(Annan&Hargreaves,2013),causinganequatorwardcontractionofthetemperaturegradients.
(Allenetal.,2012)18
Conclusions
• Bothobservationsandclimatesimulationsindicatethatthewidthofthetropics followsthemeridionalvariationsofsubtropicalfronts.
• Underglobalwarming,thesubtropicalfrontsadvancetowardspoles duetoenhancedwarmingoverthesubtropicalocean.
• Polewardadvancingofthesubtropicalfrontsshifts theedgesofthetropics,westerlies,jetstreamsandstormtrackstowardspoles.
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