VariationsinoffshoreadvectionofAmazon-Orinocoplumewatersdiagnosedwithsatellitesalinityand

altimeterdata

Séverine Fournier1,DougVandemark2,LucileGaultier3, TongLee1,Bror Jonsson2,MichelleGierach1

1NASA/CaltechJetPropulsionLaboratory,Pasadena,CA,USA2 UniversityofNewHampshire,Durham,NH,USA

3 OceanDataLab,Brest,France

Motivations&Context

• Riverdischarge often dominates regional SSSvariationsinsummer– Amazonis world’s largest discharge (0.2Sv);flowincrease starts inApril– Orinocodischarge is the4thlargest (0.04Sv)

• Horizontaladvectionofplume-dominated layers extend >1500kmfrom shore• Transportincludes freshwater,heat,biochemical material

Orinoco

Amazon

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Amazon

Orinoco

Hurricanetracks15July-15September

2010-2014

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DEPTH(m

)LONGITUDE

Coincides with TropicalcycloneintensificationJune-November – maximumplumeextension

Summer riveradvection:potentially importantfactors inair-sea coupling– SSS(density)andSSTfronts,buoyancy ofsurfacelayer,verticalstratification– Contributiontodensity-controlled pycnocline (can exceeds 40m)

• prevents exchangebetween thewarmmixedlayerandthecoldocean interior• can affectstemperature inthetropics

NorthernPlumeRegion(NPR)

Motivations&Context

ARGO

Hurricanetracks15July-15September

2010-2014

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Amazon’s NNEextensioncoincides with middleofTropicalcycloneseason15July– 15Septis minimumSSSandmax.plumeextension

Chosenstudybox->NorthernPlumeRegion(NPR)

Motivations&Context

ARGO

SMOSSSS35.5psucontour

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Amazon’s NNEextensioncoincides with middleofTropicalcycloneseason15July– 15Septis minimumSSSandmax.plumeextension

Motivations&Context

ARGO

Recent motivating studiesSSTvariationlinkedtoadvected runoffandpotentialimpactonTCformation(preconditions):

Ffield,2007(NBCringsandsurfaceheattransport)Vizy andCook,2010(atmospherechangeduetoSST-alteredocean;increasedTCs)

Pathwaysofrunoffadvection:Colesetal,2013(modeledusingROMS,drifterdata)

Potentialupperocean-atmosphereinteractionswithtropicalstorms:Reul etal.,2014(TCinteractionwithupperocean,saltywakes)Grodsky etal.,2012Hernandezetal.,2016(modelworkshowingsalinityimpactisweakonOHC->TC)Newinger andToumi,2015(twinmodelexperimentsshowingSSTandSSSuncoupled)

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Objective

Usesatelliteobservationstoimproveourviewofsurfaceoceanvariabilityanditscontrolsonupperoceanvariabilityanditscouplingtoatmospheric

dynamics(convection,rainfall,interactionwithTCs)

SSS,SST,currents,vectorwinds

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CanwenowmonitorthespatialandtemporaldispersaloftheAmazonandOrinocoriverplumestoevaluatetheirimpactonBLthicknessandtemperaturevariations?

Questions

OceanstateQ1:DoSSSandSSTinthisplume-impactedregion(NPR)varysubstantiallysummertosummer?Q2:DoSSSandSSTcovary thisfaroffshore– particularlyzonallywithwarmerSSTshoreward(perVizy andCook2010)?

DiagnosisQ3:CanweusesatelliteSSSandoceancurrent(OSCAR)observationstotracenear-surfaceadvectionofdischargeforweeks-monthsinthisdynamicregion?Q4:Whichphysicalcontrolsdominateinterannual SSS(&SST)variability:- changesinriverrunoff?- changesinNBCring/plumeinteractions?- changesinlocalwinds?

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Data:observations

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TracerMethods• ForwardorbackwardLagrangian advectionbasedonAVISO&OSCARsurfacecurrents,

locallyinterpolated,timestep=0.2days

• Co-registerphysicalOBSERVATIONSwithtracerseachday

ESASMOSSSS:10-day,0.25° (LOCEAN,CECOS)OSTIASST:daily,0.054° (PO.DAAC)OSCARcurrents:5-day,0.33° (PO.DAAC)ASCATwindvector:nearsurface(10m),daily,0.25° (CERSAT)MODISAQUAacdm at443nm:8-dayrunningmean,9km(OceanColor)

ARGOIPRC/APDRCMLD:monthly1°x1° (IPRC/APDRC)Riverdischarge:monthlyatObidos andBolivar(OREHYBAM)Hurricanestormtrackrecord:UNYSISWEATHER

Monthly average inregion ofinterestSMOSSSS35.5psu front– AUGUST2010-2014

Monthly avg inregion ofinterest

Seasonalvariations:• fresheningfromApril-May• increaseinplumecoverage• increaseinacdm• shoalingofMLD• warmingfromwintertosummer

Interannual variations:•2010-2011,incontrastto2013-2014:

• fresherSSS• higherSST• shallowerMLD• increasedplumecoverage

•2010:• consistentlywarmerfromJanuary• higheracdm

August=Monthofpeakadvection+coincidencewithTCseason

Conv.Poten.

StrongestcovarianceofzonalSSTandSSSgradientsnearplumeedgeineachyear

SSTchangewithin (left)versusout(right)oftheplume-impacted NPRfrom April-August

shown vs.areal coverage across NPR

QuestionsOceanstate

Q1:DoSSSandSSTinthisplume-impactedregion(NPR)varysubstantiallysummertosummer?

YES- 2010-2011muchmorefreshwaterandincreasedSST- 2010muchwarmereverywhere

Q2:DoSSSandSSTcovary thisfaroffshore– particularlyzonallywithwarmerSSTshoreward?

YES- weakbutpersistentSST:SSSanticorrelation- strongestcovarianceneareasternplumeedgeinNPR- strongestin2010-2011

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Advectionandcontrols

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AdvectionBACKWARDfrom theNPRParticleslaunchedeverydayintheNPRandadvected backwardtotheOrinocoandAmazonmouths

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AdvectionBACKWARDfrom theNPRParticleslaunchedeverydayintheNPRandadvected backwardtotheOrinocoandAmazonmouths

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AdvectionBACKWARDfrom theTCregionPathway1:Amazon

Pathway2:AmazonviaOrinocoPathway3:Orinoco

BackwardLagrangian advectionfromtheNPRalong3pathways:• DominanceofAmazonversus

Orinocoadvection• Amazonpath1(direct)

dominatesoverpath2• 2014has6-8timesless

particlestracedbackvs.2010-2011

Virtualdrifterslaunchedon15June2011

Virtualdrifterslaunchedon15June2014

FORWARD

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EVALUATIONOFCONTROLSANDOBSERVEDINTERANNUALVARIABILITYFreshwaterinput

Amazondischargeremarkablyconsistentover2010-2014

Runoffvariationsdonotexplaintheinterannual variabilityinthefreshwaterdispersal

AMAZON

ORINOCO

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EVALUATIONOFCONTROLSANDOBSERVEDINTERANNUALVARIABILITYEddy-driventransport

EddyinteractionwithAmazonrunoff:•May-June2011 - cycloniceddyexportsfreshwaterofftheshelfandtotheNE

Lagrangian tracermappingofthenetparticleaccumulation:Particleslaunched(whitebox)betweenthe20thofMayandthe5thofJune,advectionstoppedonthe30th ofJune

•May-June2014 - twineddiesfunneltheflowalongthecoasttransportstaysclosertothecoastin2014vs2011

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EVALUATIONOFCONTROLSANDOBSERVEDINTERANNUALVARIABILITYCross-shorewinds

2014:NEwindsmuchstrongerthanin2010-2011

• windsallowoff-shelfNWadvectionofwaterin2010-2011

• windscontaintheplumeclosertothecoastin2014

ITCZlocation(furthersouthin2014)

• Areal coverage,SSS,&SSTofthedistalriverplumeinthenorthwestern tropicalAtlanticshowsignificant variability east ofleeward islands from 2010-2014

• Controlbyvariationinrunoff is unlikely (but2010Orinocoinfluencemight warrantfurther study)

• Likely advectioncontrolis combination ofMay-June eddy-plumeinteractionsaswell asstrength ofcross-shorewinds

• PersistentzonalSSTgradientsarelinked tofreshwater-controlledsurfacesalinity

• Interannual changesinNPRSST,plume-advection,winds,andSSSmay be tied tolarger-scale dynamics across thetropicalAtlantic(AMM,ITCZ)

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ConclusionsandPerspectives

Recent TCseasons…

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ThankYou

Thank You

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AVISOvsOSCARcurrents :anongoing work

• AVISO:geostrophic componentonly– Daily,0.25deg (SSH+/- 15dbutrecalculate everyday)– Instrumentalerror onSSH(2-3cm)– Error compared torealvelocity because theEkman componentis

missing

• OSCAR:geostrophic +Ekman component– 5-day,0.3deg (degradation ofAVISOSSHtocalculate currents ->

comparabletowhat is gained with theadditionoftheEkmancomponent?)

– Same instrumentalerror– IncertitudeontheEkman componentcomputation(highfrequency wind

(3to6h)andMLDneeded)– Introductionoftracers information(SST)->noindependance with

tracers (personal communicationPODAAC)

OSCAR should evolve todaily,0.25deg ->comparison then possible

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TRACERSUSINGNODIFFUSION

• Diffusionwould be abrownian mouvement,itonly adds noise,nophysics behind it

• Ifworking with concentrations,it would benecessary

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OurNPRregion ofinterest

Interannual variations:

•SWareausuallyfresherandwarmer•correlationfreshSSS/warmSST/highacdm

•SST-SSSinversecorrelation->relationshipbetweenplumewatersandSST

•2010:SST1°Cwarmerthanin2014

OurNPRregion ofinterest

• May2010-2011:in- plumeSSTs>28.5°C• July-Augustplumecoverage:~80%(20%greaterthanfor2012-2014)• Spring-to-summerSSTincreasewithtimeinbothcases

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Observedinterannual changestiedtolarger-scaledynamicsacrossthetropicalAtlanticOcean

Significantinterannual variation:

• ITCZlocation(furthersouthin2014)CoastalwinddirectionneartheshelfCanalternetheatfluxandwindfields(impactonspring-summerplumewatercharacteristics/advection)

• DramaticallydifferingSSToforder1°Cacrossthewholebasin(AtlanticMeridionalMode(AMM)– 2010vs2014)