Abstract:
Despiteitspotentialimportanceintheglobalclimatesystem,mixingpropertiesoftheNorthPacificlow-latitudewesternboundarycurrentsystem(LLWBC)remainedunsampleduntilveryrecently.Wereporthereonthefirstmeasurementsofturbulencemicrostructureassociatedwiththesecurrents,madeinthewesternboundaryregionofthetropicalNorthPacificeastofthePhilippines.TheresultssuggestthatthermoclinemixingintheNorthPacificLLWBCisgenerallyweakwiththediapycnaldiffusivityκρ～O(10?6)m2s?1.Thisisconsistentwithpredictionsfrominternalwave-waveinteractiontheorythatmixingduetointernalwavebreakingissignificantlyreducedatlowlatitudes.Enhancedmixingisfoundtobeassociatedwithapermanentcycloniceddy,theMindanaoEddy,butmainlyatitssouthandnorthflanks.There,κρiselevatedbyanorderofmagnitudeduetoeddy-inducedgeostrophicshear.Mixingintheeddycoreisatthebackgroundlevelwithnoindicationofenhancement.
Highlights:
ThermoclinemixingintheNorthPacificlow-latitudewesternboundarycurrentsystemisoverallveryweak
ThermoclinemixingatthesouthandnorthflanksoftheMindanaoEddywaselevatedbyanorderofmagnitudeduetoeddy-inducedshear
Theoft-usedfine-scaleparameterizationofturbulenceseemstogenerallyoverestimatethermoclinemixingintheNorthPacificLLWBC
Figure.(a)Comparisonbetweenmicrostructuremeasurementsandfine-scaleparameterizationforthethermoclineaverageddiapycnaldiffusivity(????therm)atalltheobservationsites.Agreementwithinfactorsof2and10isdesignatedbythegraybands.The95%bootstrappedconfidenceintervalsfortheestimatesfrommicrostructuremeasurementsarerepresentedbybars.(b)Original(graysmallsymbols)andbin-averagedsamples(largeopensymbols)ofthediapycnaldiffusivity(????)versusthegradientRichardsonnumber(Ri)foralltheestimatesinthethermocline.Theboldlineshowstheanalyticalapproximationdiscussedinthetextwiththe95%confidenceintervalsindicatedbygrayshading.
Citation:ZhiyuLiu*,QiangLian,FangtaoZhang,LeiWang,MingmingLi,XiaolinBai,JianingWang,FanWang.WeakThermoclineMixingintheNorthPacificLow-LatitudeWesternBoundaryCurrentSystem.GeophysicalResearchLetters,,DOI:10./GL.
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