Ocean Response. Pacific Decadal Oscillation (PDO) North Pacific Gyre Oscillation (NPGO) SSTa. SSTa. Correlation

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3 Pacific Decadal Oscillation (PDO) North Pacific Gyre Oscillation (NPGO) SSTa Ocean Response 2 Correlation SSTa

4 KOE Meridional Mode Axis of KOE Taguchi et al. 27 ocean 9 Connections to AL/PDO Alexer, 1992; 22 Newman et al., 23 Vimont et al. 25 Framework for Pacific Climate Variability AL Aleutian Low Trenberth Hurrell 1995 atmosphere (winter) Qiu et al., 27 EXTRA-TROPICS PDO Pacific Decadal Oscillation Mantua et al ocean (winter) KOE Zonal Mode Strength of KOE Taguchi et al. 27 ocean CPW Central Pacific EPW non-canonical ENSO (mature) Eastern Pacific Canonical ENSO (mature) TROPICS Di Lorenzo et al. 21 NPO North Pacific Oscillation Walker Bliss, 1932 Rogers, 1981 atmosphere (winter) Ceballos et al., 29 NPGO North Pacific Gyre Oscillation Di Lorenzo et al. 28 ocean (winter) SFM Vimont et al. 23 Anderson et al., 23 CPW Central Tropical Pacific Warming (onset)

5 Pacific Decadal Oscillation (PDO) Mantua et al. (1997) defined PDO as EOF 1st mode of monthly SSTa in North Pacific (2 N-7 N) - originally used to discuss climate impact on Salmon Production FIG. 1. Normalized winter mean (November-March) time histories ofpacificclimateindices. Dottedvertical lines aredrawn tomarkpdopolarityreversal times in 1925,1947, Positive (negative) values ofnppi correspondtoyears witha deepened(weakened) Aleutianlow. ThenegativeSOI isplottedso that it is inphasewithtropical SSTvariabilitycapturedby CTI. Positivevaluebars areblack, negativearegray. FIG. 1. Normalized winter mean (November-March) time lines aredraw n histories Pacific climpole ateindices. Dottedas vertical ZWB. of The Tahiti is defined average SLP to markaly PD Opolarity reversal timeslatitude in 1925,1947, anom from 2 N to 2 S from in-a N PPI correspond to years w ith Positive (negative) values of ternational date line to of South Cendeepened (weakened) Aleutian low.coast Thenegative SOI is plotted so tral A m erica, w hile D arw in pole is defined as that it is inphasewithtropical SSTvariabilitycapturedby SLPbars anom aly over are rem ainder of C TI. average Positivevalue areblack, negative gray. Mantua et al. (1997)

6 Sea Level Pressure anomaly (SLPa) regressed on PDO suggests that, to first order, PDO is a forced response of North Pacific ocean to atmospheric forcing by variability of Aleutian Low (AL). Aleutian Low <=> Westerly Wind <=> Ekman Transport me wn 77. ha so he me wp n L 77. n-a nso as he he Mantua et al. (1997) Fig. Contribution of u PDO T estimated from a simplified SST budget by Chhak et al. (29) This first order explanation is confirmed quantitatively to some extent by using a numerical model & a simplified budget analysis (Chhak et al., 29).

7 FIG. 14. Summary figure of basic processes involved in PDO.

8 currents, ir interannual decadal variations in Rossby wave dynamics (e.g., westward-propagating, midlatitude North Pacific (Nonaka et al. 26; Taguchi satellite-observed sea surface height anomalies; Qiu et al. 27; Nonaka et al. 28; Taguchi et al. 21; Chen 25, 21) while latter behaves as a Sasaki Schneider 211). passive tracer subject to advection by background flows Besides major oceanic datasets, we use an atmo- (e.g., southwestward propagating of spiciness anomalies 15 AUGUST 217 TAGUCHI ET AL spheric reanalysis an oceanic index: Japanese in North Pacific subtropical gyre detected in Argo 55-year (JRA-55; Kobayashivariations et al. 215) for observations; et al. (e.g., 21).westward-propagating, currents,reanalysis ir interannual decadal in Rossby wavesasaki dynamics vertically averaged over Qiu surface sensible Pacific latent(nonaka heat fluxes, 26; Oyashio Finally, Tr T x are midlatitude North et al. Taguchi satellite-observed sea surface height anomalies; 4-m depth to define spiciness Extension (OEI; et al. et 211). The upper et al. 27;index Nonaka et Frankignoul al. 28; Taguchi al. 21; Chen 25, 21) while dynamical latter behaves as a, recomponent of anomalies, OEI represents meridional shift of Oyashio Extenr xflows Sasaki Schneider 211). passive tracer subject to advection by background We choosepropagating depth range of 4 m in our sion (or SAFZ) isoceanic first principal of spectively. Besides major datasets, wecomponent use an atmo(e.g., southwestward of spiciness anomalies of to focus on gyre upperdetected ocean where Oyashio Extension in latitude for definition spheric reanalysis anposition oceanic index: Japanese in North Pacific subtropical in Argo variability affect sea surface temperature zonal sector E, which is detected lat55-year Reanalysis (JRA-55; Kobayashi et al.as215) for rmal observations; Sasakimay et al. 21). overlying itude ofsensible maximum of SST based Tx are vertically averaged over surface meridional latent heat gradient fluxes, Oyashio Finally, Tr atmosphere. on objectively air sea fluxes (OAFlux) Extension index analyzed (OEI; Frankignoul et al. 211). The upper 4-m depth to define dynamical spiciness dataset compiled for period at a component of anomalies,, reoei represents meridional shift of Oyashio Exten3. Spatiotemporal structures of decomposed r x grid et al. 28). sion (Yu (or SAFZ) is first principal component of spectively. We choose depth range of 4 m in our Effects of Rossby waves on Heat Content (-4m) Taguchi et al. (217) shows that T moves westward along Kuroshio Extension - heaving of rmocline related to Rossby waves T moves eastward along subarctic frontal zone - generated by wave-related variability V near western boudary Analysis Oyashiomethod Extension position in latitude for definition of to focus on upper ocean where b. passively mean Uinterannual decadal This by section describes varij O UlatR N A Lrmal O F C L Ivariability MATE 3 may affect sea surface Vtemperature zonal sector E, which is detected advected as 6255 First,of we removemeridional from monthly dataofofsst based Ishii itude maximum gradient analysis OFES hindcast ir linear on objectively analyzed air sea fluxes trends (OAFlux) monthly climatologies to focus on naturalatvariability dataset compiled for period a of data. The residual temperature anomalies are grid (Yu et al. 28). n decomposed into 1) temperature anomalies Tr that b. Analysis are associatedmethod with density anomalies (dynamical com that Ishii are ponent) remove 2) temperature anomalies First, we from monthly data T ofx density with salinity compoanalysis compensating OFES hindcast ir (spiciness linear trends nent). Temperature anomalies are assumed to result stard monthly climatologies to focus on natural variability from of mean field with components of displacements data. The residual temperature anomalies are deviation perpendicular to isopycnals dx parallel to dx r decomposed into 1) temperature anomalies x n Tr that isopycnals: are associated with density anomalies (dynamical com- OLUME 15 AUGUST 217 TAGUCHI ET AL. AUGUST 217 ability ofoverlying dynamical spiciness15components of, atmosphere. r x, respectively, in extratropical North Pacific Ocean represented in Ishii analysis 3. Spatiotemporal structures of decomposed OFES hindcast. TAGUCHI ET AL. variability a. Horizontal structure This section describes interannual decadal varifigures 2a 2b showspiciness interannual decadal varability of dynamical components of, x, respectively, based on iability r r of x, respectively, in extratropical Ishii analysis. Contrary to TS14 s coupled GCM in which North Pacific Ocean represented in Ishii analysis longitude-time spiciness component dominates in variofes hindcast. diagram On decadal time scales, we mustcontribute consider ability, both components to total a. Horizontal structure variability in Ishii analysis. The r variability is not only ocean response to local atmospheric forcings, large in 2asubtropics, particularly along Kuroshio that are Figures 2b show interannual decadal varponent) 2) temperature anomalies T T 5 T 2 T 2=T(x)! (dxr 1 dxx ) 5 Tr x1 Tx, (1) Extension (KE), around 358N, Subtropical density compensating salinityremotely (spiciness compo- forced iability of butwithalso variabilities r x, respectively, based on Hawaiian Lee Countercurrent, Ishii analysis. Contrary to TS14 s coupled GCM in which nent). Temperature anomalies are assumed to result Countercurrent T is monthly where T is monthly mean temperature, west norast of Hawaii, respectively, indicating /or delayed response, spiciness component dominates in varifrom displacements of mean field with components is monthly temperamean climatology of T, T variability reflects variability in that r contribute to total dxr perpendicular to isopycnals dxx parallel to ability, both components which are related dynamical response of ocean ture anomaly. Applying same approach to densityto rmocline with se On currents. variability is averagedof over isopycnals: variability in associated Ishii analysis. The ocean FIGr.content 9. (a) Longitude time spiciness ocean heat content anomaly latitudinally averaged over FIG. 7. (a) Longitude time diagram of dynamical ocean heat anomaly diagram N anomalies, noting that Tx does not impact is large in subpolar region, or h, exceeds region where stard deviationheight of based on Ishii analysis (color shading; K). Superimposed with red (blue) contours are dynamic relative to.175 K designated with cyan contour in Fig. 8, based on x large in subtropics, particularly along Kuroshio Ishii analysis (color shading;show K). (b) in (a),height but for anomaly averaged over region where hindcast contours seaas surface 2 m for.2 (2.2) m s. (b) As in (a), but based on OFES can be furr density field, aroundaround Kuroshio Oyashio confluence exceeds.4panel K based on OFES hindcast. Solid pink lines show phase lines for stard deviation T 2TTr 2=T(x)! (dxwritten 1 dxx )as 5 Tr 1 Tx, (1) particularly T 5 anomaly(ke), for 5. (25.) cm. Note that358n, color scales are different shown atof bottom of each between Extension Subtropical r with phase of cm s for Ishii analysis OFES a typical eastward propagation a phase speed speeds of (a) along (b). Solid black lines show phase line for a typicalzone. westward propagation of ofwith region subarctic frontal The North T ρcountercurrent dynamical component related to heaving respectively. 3.9 cm s. Hawaiian Lee hindcast, Countercurrent, dt dt =T! =r Pacific subarctic frontal zone is respectively, characterizedindicating by sharp T 2is where T istmonthly mean temperature, west norast ofcomponent Hawaii, r 5 5, with. monthly (2) T spiciness ρ compensating with S r χ departed off Japan (1458E) during mid-198s eastward is due to anomalies advection that of arrived North Pacificin around At lag 23 yr ini- westward propagating, negative dr dr latitude of density-compensating temperax propagation W. monthly tempera- gradients mean climatology of T, T is j=rj variability reflects variability in that pink solid lines in Fig. 9). The eastward prop spiciness by background meanincurrent North Pacific have a weak tial r in eastern at western boundary early (TS14). 198s. The with phase r in ture (.1salinity (e.g., deviation Kida et al. contours Considering difference propagation path of se signals is cm s21 for Ishii amplitude K per one stard of ref-215; propagation of in r corresponds well to that of dy r x 2 22 x 21 r r x x 21

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12 MEXT%KAKENHI%INNOVATIVE%STUDY%Ocean%Mixing%Processes%(OMIX):%% Impact%on%Biogeochemistry,%climate%%ecosystem%%(215L219)%VerNcal%mixing% %PhysicalL%ChemicalLBiologicalLIntegrated%ObservaNons%%%oceanLclimateLbiogeochemistryLecosystem% modelling%in%%northwestern%pacific%especially%in%%kuroshio%%oyashio%regions% h"p://omix.aori.u.tokyo.ac.jp Overarching Goals Explore vertical mixing in western North Pacific & impacts on circulation, biogeochemistry, climate ecosystem: Deep Circulation in N.P. quantify upwelling through vertical mixing Processes to sustain ocean ecosystem quantify transport of nutrients to ecosystem Long-period variability forecast of ocean/climate/ fisheries Reproduce bi-decadal related period variability ir mechanisms)

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16 1.12/214GL61737 he difference in SST between NODAL CTL, T, in February. (a) R nodal, nthly R nodal along 39 N. Amplitude lag are shown where R nodal is

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