Divergent Eddy Heat Fluxes in the Kuroshio Extension at ... · Divergent Eddy Heat Fluxes in the...

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!-,) !,)) !+,) ) +,) ,)) -,) ) +)) #)) &)) ’)) "))) "+)) "#)) "&)) 6789: 245 ! < "##) 4 + = !" ! < "’#+ 4 + = !" ! < +(-’ 4 + = !" ! < !"’,+ 4 + = !" ! < !"’"# 4 + = !" " + ( # , Divergent Eddy Heat Fluxes in the Kuroshio Extension at 143 o ‐149 o E Stuart P. Bishop * , D. Randolph Wa7s, Kathleen A. Donohue Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narraganse@, RI 02882 * [email protected] B1399 I. Introduc@on IV. Spa@al Structure of Divergent Eddy Heat Fluxes V. Ver@cal Structure VI. Temporal Variability VII. Summary III. Eddy Heat Fluxes: Rota@onal vs. Divergent II. Eddy Heat Flux ρ 0 C p u T = ρ 0 C p u bc T + ρ 0 C p u bt T Kuroshio Extension System Study (KESS) u = u bc + u bt CPIES Absolute Geostrophic Currents Mesoscale‐resolving array of 46 current and pressure equipped inverted echo sounders (CPIES). Located east of Japan in region of highest EKE. Provides 3‐D maps of geostrophic velocity and temperature for 16 months (Donohue et al. 2010) 1 . This poster presents eddy heat flux esZmates from the KESS observaZons. Longitude [°E] Latitude [°N] 135 140 145 150 29 30 31 32 33 34 35 36 37 38 39 40 meters !10000 !9000 !8000 !7000 !6000 !5000 !4000 !3000 !2000 !1000 0 16 Month Latitude [°N] Longitude [°E] 250x10 6 W m !1 a) 144 146 148 30 32 34 36 38 Stable Vertically!Integrated Eddy Heat Flux b) 144 146 148 Unstable c) 144 146 148 !0.1 !0.05 0 0.05 0.1 PW Poleward Eddy Heat Transport d) 16 Month Stable Unstable !500 0 500 (x10 6 ) W m !1 Latitude [°N] 500 kW m !2 (a) 400 m Full ρ0Cp uT 144 146 148 30 32 34 36 38 T 2 [ C 2 ] 5 10 15 20 (b) Rotational ρ0Cp u bcT 144 146 148 30 32 34 36 38 (c) Dynamic ρ0Cp u btT 144 146 148 30 32 34 36 38 Longitude [°C] Latitude [°N] 20 kW m !2 (d) 1500 m Full 144 146 148 30 32 34 36 38 T 2 [ C 2 ] 0 0.02 0.04 0.06 0.08 (e) Rotational 144 146 148 30 32 34 36 38 (f) Dynamic 144 146 148 30 32 34 36 38 Longitude [°E] Latitude [°E] 558 (a) 0.5 m s !1 °C 144 146 148 30 32 34 36 38 563 (b) 568 (c) 573 (d) !0.06 0 0.06 dbar Current and Pressure Equipped Inverted Echo Sounders (CPIES) KESS Mo@va@on Overview ψ ψ + u bc u bt u Eddy‐mean flow interacZons: 1. Eddies release mean potenZal energy of baroclinic jet. 2. Eddies act as an eddy force on the mean flow. $ !$ C<*DE) 7*<;<=>) ?°BA %# %" &# O9M<*DE) 789:;<=>) ?°@A 7*<;<=>) ?°BA !&# !"# !’# %# %" &# Q dyn = ρ 0 C p u bt T dz Ver@cally‐Integrated Eddy Heat Flux a) 16 month: asymmetry along mean path ‐ Down‐gradient upstream of trough ‐ Up‐gradient downstream of trough b) “Stable” regime: 1 st 6 months – mostly down‐gradient. c) “Unstable” regime: 10 months – similar to 16 month mean with asymmetry along mean path. Poleward Eddy Heat Transport d) Peaks near 35 o N at ~0.04 PW Parameteriza@on ˆ n u bt T = κ T n kW m ‐2 Cross‐stream eddy heat flux profiles Weakly depth‐dependent reference currents drive divergent fluxes Down‐gradient parameterizaZon good upstream of trough. κ ranges 1000‐3000 m 2 s ‐1 ParameterizaZon doesn’t account for up‐gradient fluxes downstream of trough. ObservaZons ParameterizaZon Ver@cal Structure VerZcally‐coherent cross‐stream fluxes peak 200‐500 m, mid‐ thermocline . Peak fluxes are in excess of ±500 kW m ‐2 . "## $ % "#& $ % "#’ $ % () $ * (" $ * (+ $ * (( $ * (# $ * (, $ * (& $ * (- $ * (’ $ * 1 2 " + ( # , .1") & 0 23 4 !" 5 !,)) !#)) !()) !+)) !")) ) ")) +)) ()) #)) ,)) ˆ n = T T ˆ n ˆ s Time Series at 400 m a) Episodic Zme series b) Days 152‐300 – 1 st 6 months “Stable” regime: Dominated by 10‐15 day low‐amplitude eastward propagaZng baroclinic waves. Heat fluxes are weak and down‐gradient. c) Days 325‐400 – Cold‐Core Ring FormaZon: Strong down‐gradient fluxes directly upstream of where the ring formed. Up‐gradient fluxes within where the ring formed and downstream. d) Days 425‐550 – Cold‐Core Ring/Jet InteracZon: Similar spaZal structure to cold‐core ring formaZon e) Days 550‐580 – Remotely‐generated abyssal eddy/jet interacZon in absence of rings: Strong down‐gradient fluxes 35 o N 145 o E. Weak up‐gradient fluxes downstream. 150 200 250 300 350 400 450 500 550 600 650 !150 !100 !50 0 50 100 150 Year Day (2004) (x10 2 ) kW m !2 (a) 400 m · 1 2 3 4 5 6 7 Latitude [°N] Longitude [°E] 500 kW m !2 (b) 152!300 1 2 3 4 5 6 7 Stable 144 146 148 30 32 34 36 38 (c) 325!400 Ring Formation 144 146 148 (d) 425!550 Ring!Jet Interaction 144 146 148 (f) 550!580 Isolated Deep Eddies 144 146 148 !2.5 !2.0 !1.5 !1.0 !0.5 0 0.5 1.0 1.5 2.0 (x10 3 ) kW m !2 ρ 0 C p ˆ n u bt T Presence of remotely‐generated deep eddies Regime ShiZ The Kuroshio Extension exhibits decadal variability within 1000 km of Japan coast (Qiu and Chen 2005) 4 . Jet axis: Thick black contour 30‐60 day band‐ pass filtered upper geopotenZal height anomaly (CI = 1 cm): Dark gray: posiZve Light gray: negaZve 30‐60 day band‐ pass filtered bo@om pressure anomaly: color contour. Eddy heat flux vectors at 400 m. Figure Legend External Deep Cyclone‐Jet: Interac@on and Heat Flux a) Deep cyclone begins crossing jet. b) Poleward heat flux associated with joint‐development between deep cyclone and upper geopotenZal height anomaly. c) Strong poleward heat flux. Joint development between upper and deep conZnues. Axis of jet steepens into a trough. d) Joint development reaches a maximum as deep cyclone passes almost completely south of jet. The eddy heat flux is the depth‐averaged density, ρ 0 , Zmes the specific heat at constant pressure, C p , Zmes the temporal correlaZon between the geostrophic currents, u, and the temperature field, T: ρ 0 C p u T CPIES Mapped Eddy Heat Flux 1) Divergent eddy heat fluxes in the Kuroshio Extension are driven by weakly depth‐dependent currents. 2) 16 month mean divergent fluxes change alongstream from down‐gradient to up‐gradient at the mean trough. 3) Fluxes are verZcally coherent with extrema exceeding 500 kW m ‐2 between 200‐500 m. 4) The mean spaZal structure arose from episodic mesoscale phenomena: cold‐core ring formaZon, ring‐jet interacZon, and remotely‐generated deep eddy‐jet interacZons. Absolute geostrophic currents are the vector sum between a verZcally aligned current in thermal‐wind balance called the baroclinic current, u bc , and a weakly depth‐dependent reference current called the barotropic current, u bt , measured at 5300 m. u bc T ˆ k ×∇ T 2 Rota@onal Fluxes The baroclinic component is completely rotaZonal (nondivergent) (Marshall and Shu@s 1981) 2 : Upper Ocean at 400 m (a‐c) Total fluxes (a) are ~2000 kW m ‐2 and comparable to the Gulf Stream (Cronin and Wa@s 1996) 3 . RotaZonal fluxes (b) dominate the total fluxes (a), follow temperature variance contours, and mask the divergent fluxes (c) which are < 25% as large. The divergent component (c) crosses the front. Subthermocline Ocean at 1500 m (d‐f) Total fluxes (d) have equal contribuZon from rotaZonal (e) and divergent (f) fluxes. RotaZonal fluxes (e) diminish with depth. Divergent fluxes are driven by the weakly depth‐ dependent reference currents. VIII. References and Acknowledgements 1. Donohue, K. A., D. R. Wa@s, K. Tracey, A. D. Greene, and M. Kennelly, 2010. Mapping circulaZon in the Kurohsio Extension with an array of Current and Pressure recording Inverted Echo Sounders. J. Atmos. Oceanic Technol., 27:507‐527. 2. Marshall, J., and G. Shu@s, 1981. A note on rotaZonal and divergent eddy fluxes. J. Phys. Oceanogr., 11, 1677‐1680. 3. Cronin, M., and D. R. Wa@s, 1996. Eddy‐mean flow interacZons in the Gulf Stream at 68oW. Part I: Eddy EnergeZcs. J. Phys. Oceanogr., 26, 2107‐2131. 4. Qiu, B., and S. Chen, 2005. Variability of the Kuroshio Extension jet, recirculaZon gyre and mesoscale eddies on decadal Zmescales. J. Phys. Oceanogr., 35, 2090‐2103. This work was supported under NSF grants OCE‐0221008 and OCE‐0851246 The Kuroshio Extension differs from the Gulf Stream in that it has a shallower thermocline and it flows over a much deeper subthermocline layer. As a result, meander growth through self development that has been observed in the Gulf Stream is not as effecZve in the Kuroshio extension. Instead, meander growth and decay processes are driven by external mesoscale perturbaZons. The largest down‐ and up‐gradient eddy heat fluxes are driven by remotely‐generated deep eddies and ring interacZons with the Kuroshio Extension. (0.5 m s ‐1 o C = 2055 kW m ‐2 )

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DivergentEddyHeatFluxesintheKuroshioExtensionat143o‐149oEStuartP.Bishop*,D.RandolphWa7s,KathleenA.Donohue

GraduateSchoolofOceanography,UniversityofRhodeIsland,215SouthFerryRoad,Narraganse@,RI02882*[email protected]

B1399

I.Introduc@on

IV.Spa@alStructureofDivergentEddyHeatFluxes V.Ver@calStructure

VI.TemporalVariability VII.Summary

III.EddyHeatFluxes:[email protected]

ρ0Cp ′ u ′ T = ρ0Cp ′ u bc ′ T + ρ0Cp ′ u bt ′ T

KuroshioExtensionSystemStudy(KESS)

u = ubc + ubt

CPIESAbsoluteGeostrophicCurrents

• Mesoscale‐resolvingarrayof46currentandpressureequippedinvertedechosounders(CPIES).• LocatedeastofJapaninregionofhighestEKE.• Provides3‐Dmapsofgeostrophicvelocityandtemperaturefor16months(Donohueetal.2010)1.• ThisposterpresentseddyheatfluxesZmatesfromtheKESSobservaZons.

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a)  16month:asymmetryalongmeanpath‐Down‐gradientupstreamoftrough‐Up‐gradientdownstreamoftrough

b)  “Stable”regime:1st6months–mostlydown‐gradient.

c)  “Unstable”regime:10months–similarto16monthmeanwithasymmetryalongmeanpath.

PolewardEddyHeatTransportd)Peaksnear35oNat~0.04PW

Parameteriza@on

ˆ n ⋅ ′ u bt ′ T = −κ∂T ∂n

kWm‐2

Cross‐streameddyheatfluxprofiles

Weaklydepth‐dependentreferencecurrentsdrivedivergentfluxes

•  Down‐gradientparameterizaZongoodupstreamoftrough.

•  κranges1000‐3000m2s‐1

•  ParameterizaZondoesn’taccountforup‐gradientfluxesdownstreamoftrough.ObservaZons

ParameterizaZon

Ver@calStructure•  VerZcally‐coherentcross‐stream

fluxespeak200‐500m,mid‐thermocline.

•  Peakfluxesareinexcessof±500kWm‐2.

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TimeSeriesat400ma)  EpisodicZmeseriesb)  Days152‐300–1st6months“Stable”regime:‐  Dominatedby10‐15daylow‐amplitude

eastwardpropagaZngbaroclinicwaves.‐  Heatfluxesareweakanddown‐gradient.c)  Days325‐400–Cold‐CoreRingFormaZon:‐  Strongdown‐gradientfluxesdirectlyupstream

ofwheretheringformed.‐  Up‐gradientfluxeswithinwheretheringformed

anddownstream.d)  Days425‐550–Cold‐CoreRing/JetInteracZon:‐  SimilarspaZalstructuretocold‐corering

formaZone)  Days550‐580–Remotely‐generatedabyssal

eddy/jetinteracZoninabsenceofrings:‐  Strongdown‐gradientfluxes35oN145oE.‐  Weakup‐gradientfluxesdownstream.

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RegimeShiZ

TheKuroshioExtensionexhibitsdecadalvariabilitywithin1000kmofJapancoast(QiuandChen2005)4.

•  Jetaxis:Thickblackcontour

•  30‐60dayband‐passfiltereduppergeopotenZalheightanomaly(CI=1cm):

‐  Darkgray:posiZve‐  Lightgray:negaZve•  30‐60dayband‐

passfilteredbo@ompressureanomaly:colorcontour.

•  Eddyheatfluxvectorsat400m.

FigureLegend

ExternalDeepCyclone‐Jet:Interac@onandHeatFlux

a)  Deepcyclonebeginscrossingjet.b)  Polewardheatfluxassociatedwithjoint‐developmentbetweendeepcyclone

anduppergeopotenZalheightanomaly.c)  Strongpolewardheatflux.‐  JointdevelopmentbetweenupperanddeepconZnues.‐  Axisofjetsteepensintoatrough.d)  Jointdevelopmentreachesamaximumasdeepcyclonepassesalmost

completelysouthofjet.

•  Theeddyheatfluxisthedepth‐averageddensity,ρ0,Zmesthespecificheatatconstantpressure,Cp,ZmesthetemporalcorrelaZonbetweenthegeostrophiccurrents,u,andthetemperaturefield,T:

ρ0Cp ′ u ′ T

CPIESMappedEddyHeatFlux

1)  DivergenteddyheatfluxesintheKuroshioExtensionaredrivenbyweaklydepth‐dependentcurrents.

2)  16monthmeandivergentfluxeschangealongstreamfromdown‐gradienttoup‐gradientatthemeantrough.

3)  FluxesareverZcallycoherentwithextremaexceeding500kWm‐2between200‐500m.

4)  ThemeanspaZalstructurearosefromepisodicmesoscalephenomena:cold‐coreringformaZon,ring‐jetinteracZon,andremotely‐generateddeepeddy‐jetinteracZons.

•  AbsolutegeostrophiccurrentsarethevectorsumbetweenaverZcallyalignedcurrentinthermal‐windbalancecalledthebarocliniccurrent,ubc,andaweaklydepth‐dependentreferencecurrentcalledthebarotropiccurrent,ubt,measuredat5300m.

′ u bc ′ T ∝ ˆ k ×∇ ′ T 2

Rota@onalFluxes•  ThebarocliniccomponentiscompletelyrotaZonal

(nondivergent)(MarshallandShu@s1981)2:

UpperOceanat400m(a‐c)•  Totalfluxes(a)are~2000kWm‐2andcomparabletothe

GulfStream(CroninandWa@s1996)3.•  RotaZonalfluxes(b)dominatethetotalfluxes(a),follow

temperaturevariancecontours,andmaskthedivergentfluxes(c)whichare<25%aslarge.

•  Thedivergentcomponent(c)crossesthefront.

SubthermoclineOceanat1500m(d‐f)•  Totalfluxes(d)haveequalcontribuZonfromrotaZonal

(e)anddivergent(f)fluxes.•  RotaZonalfluxes(e)diminishwithdepth.

•  Divergentfluxesaredrivenbytheweaklydepth‐dependentreferencecurrents.

VIII.ReferencesandAcknowledgements1.  Donohue,K.A.,D.R.Wa@s,K.Tracey,A.D.Greene,andM.Kennelly,2010.MappingcirculaZonintheKurohsioExtension

withanarrayofCurrentandPressurerecordingInvertedEchoSounders.J.Atmos.OceanicTechnol.,27:507‐527.2.  Marshall,J.,andG.Shu@s,1981.AnoteonrotaZonalanddivergenteddyfluxes.J.Phys.Oceanogr.,11,1677‐1680.3.  Cronin,M.,andD.R.Wa@s,1996.Eddy‐meanflowinteracZonsintheGulfStreamat68oW.PartI:EddyEnergeZcs.J.

Phys.Oceanogr.,26,2107‐2131.4.  Qiu,B.,andS.Chen,2005.VariabilityoftheKuroshioExtensionjet,recirculaZongyreandmesoscaleeddiesondecadal

Zmescales.J.Phys.Oceanogr.,35,2090‐2103.

ThisworkwassupportedunderNSFgrantsOCE‐0221008andOCE‐0851246

TheKuroshioExtensiondiffersfromtheGulfStreaminthatithasashallowerthermoclineanditflowsoveramuchdeepersubthermoclinelayer.Asaresult,meandergrowththroughselfdevelopmentthathasbeenobservedintheGulfStreamisnotaseffecZveintheKuroshioextension.Instead,meandergrowthanddecayprocessesaredrivenbyexternalmesoscaleperturbaZons.Thelargestdown‐andup‐gradienteddyheatfluxesaredrivenbyremotely‐generateddeepeddiesandringinteracZonswiththeKuroshioExtension.

(0.5ms‐1oC=2055kWm‐2)