1 Dynamics of the Tsuchiya Jets Ryo Furue ( 古恵 亮, IPRC, U of Hawaii)‏ In collaboration with Jay McCreary, Zuojun Yu & Dailin Wang

2 Introduction

3 Observed Tsuchiya Jets Johnson et al. (2002)‏Thermostad Eq. 8S 8N 400m 0m 165 o E (west)‏ 155 o W (center)‏ 110 o W (east)‏ u T TJs Eq. 8S 8N Eq. 8S 8N TJs shift poleward and to higher temperatures as they flow eastward

4 Fate of sTJ The fate of the southern TJ is not clear. Recirculates to flow westward in EIC (Rowe et al. 2000)? Upwells at the coast of Peru? The “primary” sTJ recirculates and “secondary” sTJ upwells at Peru (Ishida et al. 2005)?

5 nTJ and the Costa Rica Dome Kessler (2002, 2006)‏ nTJ transport ≈ 6 Sv CRD upwelling ≈ 3 Sv nTJ is a beta plume driven by CRD upwelling?

6 Theories Conservation of angular momentum (Marin et al. 2000, 2003; Hua et al. 2003). Eddy forcing (Jochum & Malanotte- Rizzoli 2004). McPhaden-type linear dynamics (McPhaden 1984; McCreary 1981). Inertial jet (Johnson & Moore 1997). Arrested front (McCreary et al. 2002).

7 Arrested fronts McCreary et al.’s (2002) 2 ½-layer model: Layer 2 contains the TJ; Streamfunction h  characteristics: u g and v g are geostrophic components of Sverdrup flow; v g bends characteristics meridionally; Arrested front occurs where characteristics overlap.

8 Northern TJ as arrested front (McCreary et al. 2002)‏ vgvg Recirculation around a patch of upwelling driven by wind curl forms a near-equatorial front due to the bending of characteristics. Eq. 30N 100° 0°0°0°0° AnalyticalNumerical

9 Objective To determine if “arrested-front” TJs exist in an OGCM. Arrested-front solutions are reproduced. Plus some new features.

10 Ocean model

11 Model & Configuration COCO 3.4 (Hasumi at CCSR, U Tokyo)‏ 2 o × 1 o × 36 levels  no eddies. Box ocean: 100 o × [40 o S–40 o N] × 4000 m Constant salinity. Eq. 40N 40S wEwE 100 o Northern TJ

12 Forcing Inflow of cool water (14 o C–6 o C) thru the s.b. (7.5 Sv)‏ Outflow of warm water thru the w.b. at 2 o N–6 o N. SST: relaxed to T*(y) = 15 o C–25 o C. Basin-wide  x, representing trades.  y  coastal upwelling in the south Pac.  e, “Costa Rica Dome” wind patch. Must upwell!

13 Mixing P.-P. vertical diffusion with  b = 0. Isopycnal diffusion (10 7 cm 2 /s); K H = 0.  diffusive only when |dz/dx| > critical. Laplacian horizontal viscosity (10 8 cm 2 /s) with 20×10 8 cm 2 /s in the WBL. Third-order upstream advection scheme  weakly diffusive. To minimize diffusion…

14 Northern TJ

15 No wind The inflow water flows along the southern and western boundaries and directly exists through the outflow port.

16 CRD patch only 14 o C–6 o C CRD

17 CRD patch only 14 o C–6 o C CRD  y CRD

18 Standard solution

19 Sublayers (lower)‏ 10 o C–9 o C 11 o C–10 o C

20 Sublayers (upper)‏ 12 o C–11 o C 14 o C–12 o C

21 Summary of the nTJ solutions The summary is almost the same as that of sTJ. A nTJ and thick thermostad are reproduced. The hierarchy of solutions agrees with 2½ -layer ones. The nTJ becomes warmer to the east because it is supplied by water that diverges from the lower part of the EUC. But, there is one more interesting thing….

22 Beta plume and eddy form stress

23 Vertical structure of the subsurface recirculation gyres Why is the nTJ so deep? What drives the other, cyclonic recirculation gyre?  Eddies (slow instability waves in the CRD region with a period ~1 yr). An extended beta plume:  V = fw e U x + V y =  w e + curl  form stress 

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25 Beta plume driven by w e Subsurface circulation U s from OGCM and from diag. model Subsurface recirculation gyre is a beta plume driven by w e.

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27 Alternative formalisms of eddy flux Eddy form stress ( F* ): vertical transfer of horizontal momentum. Bolus transport ( U* ). Isopycnal PV flux. Under geostrophy, these formalisms are largely equivalent (Greatbatch 1998). curl F* ≈ f div U*, f u* = – hq u 

28 Alternative formalisms (cont’d)‏ In our  e –only solution, curl F* ≈ f div U* holds, and a similar diagnostic model driven by the OGCM’s div U* reproduces the subsurface recirculation. U* & div U*

29 Subsurface circulation regimes Strong forcing regime (Haidvogel & Rhines 1983; Berloff 2005)‏ Under direct forcing; Upgradient (northward) PV flux; Southward bolus flux; Eastward acceleration in the middle. eddy PV flux

30 Circulation regimes (cont’d)‏ Weak forcing regime (Rhines & Holland 1979; Berloff 2005)‏ Under indirect forcing; Downgradient (souththward) PV flux; Northward bolus flux; Westward acceleration in the middle. eddy PV flux

31 Eddy PV flux ~  U* Baroclinic instability (mean PV gradient inversion)‏

32 Conclusions A non-eddy-permitting OGCM reproduces TJs with properties similar to those for arrested fronts. The deep part of EUC leaves the equator to be the top part of the TJs.  eastward warming of the TJs. Eddy form stress drives a deep, cyclonic and anticyclonic gyres.

33 Conclusions (cont’d)‏ Diffusion of any sort acts to erode the thermostad and, hence, to weaken the TJs.