Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
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
2
Amazon
Orinoco
Hurricanetracks15July-15September
2010-2014
3
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
4
Amazon’s NNEextensioncoincides with middleofTropicalcycloneseason15July– 15Septis minimumSSSandmax.plumeextension
Chosenstudybox->NorthernPlumeRegion(NPR)
Motivations&Context
ARGO
SMOSSSS35.5psucontour
5
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)
6
Objective
Usesatelliteobservationstoimproveourviewofsurfaceoceanvariabilityanditscontrolsonupperoceanvariabilityanditscouplingtoatmospheric
dynamics(convection,rainfall,interactionwithTCs)
SSS,SST,currents,vectorwinds
7
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?
8
Data:observations
9
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
15
Advectionandcontrols
17
AdvectionBACKWARDfrom theNPRParticleslaunchedeverydayintheNPRandadvected backwardtotheOrinocoandAmazonmouths
18
AdvectionBACKWARDfrom theNPRParticleslaunchedeverydayintheNPRandadvected backwardtotheOrinocoandAmazonmouths
19
AdvectionBACKWARDfrom theTCregionPathway1:Amazon
Pathway2:AmazonviaOrinocoPathway3:Orinoco
BackwardLagrangian advectionfromtheNPRalong3pathways:• DominanceofAmazonversus
Orinocoadvection• Amazonpath1(direct)
dominatesoverpath2• 2014has6-8timesless
particlestracedbackvs.2010-2011
Virtualdrifterslaunchedon15June2011
Virtualdrifterslaunchedon15June2014
FORWARD
20
EVALUATIONOFCONTROLSANDOBSERVEDINTERANNUALVARIABILITYFreshwaterinput
Amazondischargeremarkablyconsistentover2010-2014
Runoffvariationsdonotexplaintheinterannual variabilityinthefreshwaterdispersal
AMAZON
ORINOCO
21
EVALUATIONOFCONTROLSANDOBSERVEDINTERANNUALVARIABILITYEddy-driventransport
EddyinteractionwithAmazonrunoff:•May-June2011 - cycloniceddyexportsfreshwaterofftheshelfandtotheNE
Lagrangian tracermappingofthenetparticleaccumulation:Particleslaunched(whitebox)betweenthe20thofMayandthe5thofJune,advectionstoppedonthe30th ofJune
•May-June2014 - twineddiesfunneltheflowalongthecoasttransportstaysclosertothecoastin2014vs2011
22
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)
23
ConclusionsandPerspectives
Recent TCseasons…
24
ThankYou
Thank You
25
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
26
27
TRACERSUSINGNODIFFUSION
• Diffusionwould be abrownian mouvement,itonly adds noise,nophysics behind it
• Ifworking with concentrations,it would benecessary
28
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
31
Observedinterannual changestiedtolarger-scaledynamicsacrossthetropicalAtlanticOcean
Significantinterannual variation:
• ITCZlocation(furthersouthin2014)CoastalwinddirectionneartheshelfCanalternetheatfluxandwindfields(impactonspring-summerplumewatercharacteristics/advection)
• DramaticallydifferingSSToforder1°Cacrossthewholebasin(AtlanticMeridionalMode(AMM)– 2010vs2014)