1. Interactions between the Indonesian
Throughflow and circulations in the
Indian and Pacific Oceans
Jay McCreary, Toru Miyama, Ryo Furue
Tommy Jensen, Hyoun-woo Kang,
Bohyun Bang, Tangdong Qu
I highlight the word “interactions” because the ITF both impacts and is impacted by flows in the Indian and Pacific Oceans.
For example, I will argue that the Pacific Ocean is the reason that the ITF exhibits two cores.
Conversely, the ITF is a strong contributor to the near-surface eastward flows in the SIO. It may also be the cause of the Great Barrier Reef Undercurrent (GBRUC).
A short course on:
Modeling IO processes and phenomena
University of Tasmania
Hobart, Tasmania
May 4–7, 2009 1

2. References
(PTNE) McCreary, J.P., T. Miyama, R. Furue, T. Jensen, H.-W. Kang, B. Bang, and T. Qu, 2007: Interactions between the ITF and circulations in the Indian and Pacific Oceans. Prog. Oceanogr., 75(1), 70–114.
Godfrey, J.S., and A.J. Weaver, 1991: Is the LC driven by Pacific heating and winds? Prog. Oceanogr., 27, 225–272.
Hirst, A.C., and J.S. Godfrey, 1993: The role of the ITF in as global ocean GCM. J. Phys. Oceanogr., 23, 1057–1086.
Hirst, A.C., and J.S. Godfrey, 1994: The response to a sudden change in the ITF in a global ocean GCM. J. Phys. Oceanogr., 24, 1895–1910.
Wajsowicz, R., 1995: The response of the Indo-Pacific throughflow to interannual variations in the Pacific wind stress. Part I: Idealized geometry and variations. J. Phys. Oceanogr., 25, 1805–1826.
Godfrey, J.S., The effects of the Indonesian Throughflow on ocean circulation and heat exchange with the atmosphere: a review. J. Geophys. Res., 101, 12217–12237.
The talk is based entirely on discussions in the “paper that never ends” (PTNE). But there is a large amount of literature on the subject, including several review papers.

3. 1) Why is most of the IT surface trapped in the upper 400 m, with indications of a second deep core?
2) Why does the near-surface flow in the IT come from the North Pacific, and the deep core from the South Pacific?
3) What processes account for remote impacts of the IT in the Indian and Pacific Oceans?
4) What processes transform the shallow, warm IT to deep, cool, South Pacific inflow, and vice versa?
5) What, then, is the impact of the IT on subthermocline circulations in the Pacific, particularly on the flow of thermostad water and AAIW?
What drives the IT (Question 0)? The answer is Godfrey’s Island Rule. The reference is: Godfrey, J.S., A Sverdrup model of the depth-integrated flow for the World Ocean allowing for island circulations. Geophys. Astrophys. Fluid Dyn., 45, 89–112.
The processes that account for remote impacts of the ITF in the Indian and Pacific Oceans, of course, are the propagation of Rossby and Kelvin waves.
The processes that transform deep water in the Pacific to shallow ITF water MUST be upwelling (Question 4). Where does that upwelling occur? Conversely, the processes that transform shallow ITF water into the deep waters that enter the Pacific MUST be subduction, convective overturning, or subsurface diffusive mixing (Question 4).
HG did not discuss the issue of why the deep IT core comes from the SP, only why the surface core comes from the NP (Question 2). HG also did not discuss baroclinic transformations in the Pacific (Question 4).
Wajsowicz (1995) investigated ITF dynamics using an idealized OGCM. Among other things, she considered the IT transport with and without sills in the Indonesian seas. Surprisingly to me, the ITF remained surface trapped without the sills and its transport only increased slightly. This insensitivity indicates that the vertical structure of the ITF is, to a large degree, NOT determined by bottom topography.
Wajsowicz (1995) contributed to 1), contrasting surface trapping in solutions to an idealized OGCM with and without Indonesian sills.
Hirst and Godfrey (HG; 1993, 1994) addressed the near-surface flow in 2), and noted the propagation of baroclinic waves and their damping in 3).

4. Model overview Results Summary LCS model, LOM, COCO Dynamics
Basic processes
Indonesian Seas
IT vertical structure and source waters
Indian Ocean
SICC
Pacific Ocean
GBRUC, TJs, AAIW
Summary
Model overview
LCS model, LOM, COCO
We use a hierarchy of models (LCS → LOM → COCO). Also circulations are model dependent, so we consider 3 model types. A key difference among the models is their treatment of vertical mixing, with the LCS having the most simple and most unrealistic mixing.
The discussion of Dynamics and Indonesian Seas is an extension of HG (1993, 1994).
COCO = “CCSR Ocean COmponent” model;” CCSR = “Center for Climate System Research”

5. Model overview:
A hierarchy of models

6. LCS model
Linear, continuously stratified system with diffusion by vertical mixing
Linearized about a state of rest with background density ρb(z)
Solutions are expansions in barotropic and baroclinic modes (N = 25)
Forced by ERA15 and HR winds in Indo-Pacific domain
Solutions found with open and closed IT passages, and their difference illustrates the IT-associated circulation
Integrations for 100 years
The most important difference among the models is their parameterization of vertical mixing.
LOM
4½-layer model with diffusion by transfer between layers where they are thin
Layers 1–4 are surface, thermocline, thermostad waters, and AAIW.
Forced by ERA15 winds in Indo-Pacific domain
Solutions found with open and closed IT passages
Integrations for 100 years
Solutions with open passages, without open passages, and their difference are indicated by Q, Q’, and ΔQ, respectively.
Note the potential confusion between solutions Q, Q’, and ΔQ.
Mostly, I will talk about solutions to the simplest model, the LCS model, essentially a linear GCM. It assumes a background density ρb(z).
LOM is the least diffusive of the models. Its diffusion occurs only in special locations where layer thicknesses become thin.
COCO
Non-eddy-resolving GCM with a horizontal resolution of 1°×1° and 40 levels
Forced by HR winds in Indo-Pacific domain
Solutions found with open and closed IT passages
Integrations for 80 years

7. How does the IT impact circulations in the IO and PO?
Dynamics
Basic processes
How does the IT impact circulations in the IO and PO?
In this part of the talk, I show difference solutions to the LCS model, when the Indonesian passages are suddenly opened.
The next slide shows a movie of what happens when the ITF passages are suddenly opened. The influence spreads around the basin via Kelvin and Rossby waves.

8. Courtesy of Toru Miyama
LCS: Δd, n = 1 mode
The other baroclinic modes respond similarly, but are increasingly weakened by damping, which strengthens with n.
What happens when the passages are opened? A) Kelvin waves spread around Australia, along the equator, and American coasts. B) Rossby waves propagate back into the interior of the Indian and Pacific Oceans.
Radiation of Rossby and Kelvin waves plus damping.
Note that there is an impact in the northern IO. How did that happen? It did so by the radiation of Rossby waves across the basin at the latitude of the IT, equatorward and eastward propagation via coastal and equatorial Kelvin waves, and then reflection of a Rossby-wave packet from the eastern boundary.
Courtesy of Toru Miyama

9. LCS: Δd, n = 0–3 modes n = 0 n = 1 n = 3 n = 2
Barotropic flow confined to the perimeter of the southern IO and western boundaries of Australia and New Guinea.
Rossby and Kelvin waves are undamped for the n = 0 mode, and so pressure (sea level) is flat in the interior of the Indian Ocean north and south of the ITF, and in the Pacific interior.
The baroclinic modes are damped by vertical mixing, the strength of the damping increasing with modenumber n.
Damping of baroclinic Rossby waves by diffusion allows interior flows in both basins, with flows becoming weaker and more coastally confined as damping increases.

10. LCS: Δd, all modes
The IT has a basin-wide impact on circulations in both oceans. It is largest in the southern Indian Ocean and in the tropical Pacific.
Sea level rises in IO and decreases in PO.
There are surface geostrophic currents flowing along lines of constant Δd. Only around the perimeter of the IO and along the west coast of Australia is there a NET TRANSPORT (from the barotropic mode). In the interior of both basins, then, where there are only baroclinic currents, the surface currents are balanced by subsurface currents in the opposite direction.
Note that there is a circulation that extends across the model domain south of Australia, similar to the wind-driven “supergyre.”
There are surface geostrophic currents flowing along lines of constant Δd. Because the baroclinic modes have no net transport, surface currents in the interior ocean are balanced by subsurface currents in the opposite direction.

11. LCS: Δd, all modes, IO
There is a southeastward surface (northwestward subsurface) geostrophic flow across the interior of the South IO. They act to deepen the ITF transport, around the perimeter of the IO.
There is anomalous downwelling (damping) caused by the ITF in the South IO wherever Δd is positive. This process is not physically correct.
There is a circulation near the west coast of Australia similar to the Leeuwin Current system, with surface (subsurface) poleward (equatorward) flow? It is too weak, however, because, for realistic damping , the coastal signal is carried too far offshore by RWs (McCreary and Kundu, 1987).
Note that downwelling is large where Δd is high, so is strongest in the NE corner of the SIO.
The interior currents drain water from the ITF at the surface, and add to it at depth. So, the diffusion in this model is causing the transport of the IT to DEEPEN as it flow around the perimeter of the IO.
Downwelling occurs wherever Δd is positive, which is not physically correct. In the real ocean, downwelling happens via subduction and convective overturning.
Does the model make a Leeuwin Current and Undercurrent? This solution essentially shows the model situation of McCreary and Kundu (1987), who considered the flows generated in an LCS model with damping forced by an imposed ITF. An LC and LUC are produced but they are weak because RWs carry the coastal flows offshore so efficiently that a narrow, strong, coastal jet is not produced.
There is southeastward geostropic flow across the SIO, whereas the observed flow is eastward or northeastward.

12. LCS: IO transport profiles
The baroclinic interior flow acts to deepen the circulation around the perimeter of the southern IO

13. LCS: Δd, all modes, PO
There is a westward and equatorward surface (eastward and poleward) geostrophic flow across PO interior. They act to shallow the ITF transport as it flows northward along the east coast of Australia.
These general structures of circulation, upwelling and downwelling are similar among all the models. But details of the baroclinic currents differ markedly because of different diffusion parameterizations.
Upwelling is largest where Δd is lowest. So, there is still significant upwelling throughout the interior of the PO. Too much!
Not physically correct, since upwelling happens primarily in regions of Ekman suction (coast or open ocean). Some diffusion can occur in the interior ocean due to internal diffusion, but it tends to be weaker than that due to wind-driven upwelling.
Indeed, in our LOM and COCO solutions most upwelling occurs in the tropical Pacific and in the NP Subpolar Gyre.
There is anomalous upwelling caused by the ITF in the Pacific wherever Δd is negative. This process is not physically correct.

14. LCS: PO transport profiles
The interior flow in the South Pacific shallows the northward western boundary currents along the east coasts of Australia and New Guinea, eventually transforming them to the surface-trapped IT profile

15. How does the PO impact the IT?
Indonesian Seas
Vertical structure
How does the PO impact the IT?
1) In this part, I discuss how the currents in the interior of the Pacific Ocean impact the IT, both its vertical structure and its source waters.

16. There is deep flow from the SP (dashed) and surface flow from the NP (solid).
Simplify islands and block pathways to SCS! But we know there is an SCS throughflow, but not how much.

17. Because of subsurface currents in the interior Pacific.
Mean Nb, strong mixing
Eq. Nb, strong mixing
Eq. Nb, weak mixing
Eq. Nb, 4th-order mixing
LCS: ITF profiles
Velocity profiles are sensitive to the strength of vertical diffusion (damping of baroclinic waves) and the background stratification.
When diffusion is sufficiently weak, the ITF is surface trapped because the low-order baroclinic modes tend to cancel the barotropic response at depth.
Comment on the effects of each change in going from green to red curves. Note that only for the weak mixing cases does the flow at depth tend to zero. This suggests that the bottom topography in the Indonesian Seas DOES have some impact on setting the depth of the ITF.
Why does the ITF have two cores? In this model, it is clearly because subsurface eastward currents in the Pacific drain water from the Indonesian Seas.
Note that the ITF current is negative for the green and blue curves, indicating a flow FROM the IO to the PO at those depths.
All of the profiles have a subsurface velocity minimum or reversal. As a result, the ITF has two cores. Why?
Because of subsurface currents in the interior Pacific.

18. LCS: u section, far-western Pacific
u(x,160˚E,z)
Eastward currents north of about 2˚N (Halmahera) and centered near 200 m drain water from western Pacific, thereby weakening the IT at those depths. Draining by the shallower, stronger, eastward current (NECC) is balanced by flow from the NGCC or NEC, and so does not weaken the IT.
Flows that cannot be balanced horizontally are the currents that drain water from the ITF. They are upwelling-driven currents that are not part of the Sverdrup flow.
The currents near 200 m and 2N (intersection of dashed lines) are the primary flows that drain water from the IT. The much stronger, shallower currents tend to balance themselves.
The nature of the subsurface flows that drain IT water are sensitive to diffusion, and so vary from model to model.

19. How does the PO impact the IT?
Indonesian Seas
Source waters
How does the PO impact the IT?
1) In this part, I discuss how the currents in the interior of the Pacific Ocean impact the IT, both its vertical structure and its source waters. 19

20. Almost all of ψ comes from the northern hemisphere. Why?
Streamfunction ψ' is obtained with closed passages. It is the part of ψ that is driven by winds in the interior of the Pacific. Streamfunction Δψ is the part of ψ caused by the ITF. ΔΨ
Ψ', closed
LCS: Hellerman winds
Almost all of ψ comes from the northern hemisphere. Why?
The anticlockwise circulation within the Sulawesi Sea is part of the NP Tropical Gyre. It is present there because the latitude, y0, which divides the NP and SP Tropical Gyres (ψ' = 0), is near 2°N, south of the entrance to the Sulawesi Sea.
Ψ, open
Note the anticlockwise circulation in the Sulawesi Sea in Ψ’. Its eastward branch essentially cancels the westward IT flow of ΔΨ.
The two parts sum almost to cancel the flow in the southern part of the Sulawesi Sea, ensuring that the total transport comes from the north.

21. Now, almost all of ψ comes from the southern hemisphere. Why?ΔΨ
Ψ′, closed
Streamfunction ψ′ no longer has a strong anticlockwise circulation in the Sulawesi Sea. So, it cannot cancel the westward current of Δψ north of Sulawesi. Why not?
LCS: ERA15 winds
Now, almost all of ψ comes from the southern hemisphere. Why?
Latitude y0 is now near 3.7°N, so that part of the SP Tropical Gyre is present in the Sulawesi Sea.
Ψ, open
Now, there is now anticyclonic circulation in the Sulawesi Sea in Ψ’. So, the westward flow in the southern Sulawesi Sea associated with ΔΨ cannot be cancelled. 21

22. ERA15 and QSCAT winds ERA15 QSCAT
The region is absent in the QSCAT winds. It is also absent in the Hellerman winds.
QSCAT
ERA15
There is a region of strong negative curl south of the Philippines. It generates a shallow clockwise circulation in the Sulawesi Sea strong enough to eliminate the anticlockwise flow driven by winds in the interior Pacific.

23. LCS: Hellerman winds v(x,y,0), v(x,y,-300 m), open open
Subsurface flow comes from the southern hemisphere, because transport ψ′ is weak at depth so that it is dominated by Δψ.
The vertical distributions of Ψ’ and ΔΨ are different, the former being confined within and above the thermocline and the latter extending to intermediate depths.
As a result, the surface flow is strongly impacted by Ψ’ and hence comes from the north, and the subsurface flow is dominated by ΔΨ and so comes from the south.
The surface flow all comes from the northern hemisphere, because transport of ψ′ is concentrated near the surface and so dominates Δψ .

24. COCO: HR winds Ψ
The total transport comes entirely from the north because the NGCC retroflects before it can penetrate into the Indonesian Seas, apparently because horizontal viscosity is so large and the inertial overshoot of the MC.
hv1+2, open
Layers defined by σθ = 26.5, 27.0, 27.4, the bottoms of layers 1+2, 3, and 4, respectively.
As in the LCS and LOM solutions, the shallow IT comes from the north and the deep flow comes from the south.
hv4, open

25. South Indian Countercurrent How does the IT impact the IO?
Indian Ocean
South Indian Countercurrent
How does the IT impact the IO?
Recently, researchers have noted the presence of eastward flows across the interior of the IO. These flows are directed opposite to the expected Sverdrup circulation (which does appear below the surface) and the Ekman drift.
The flow tends to separate into two eastward currents: 1) the SICC across the interior of the South IO near 25ºS, and 2) the Eastern Gyral Current (EGC), farther north but still south of the equator.

26. LCS: Δd
There is no SICC jet-like flow, but rather a broad, southeastward flow across the basin, because the downwelling is not localized.
There is no SICC jet-like flow, but rather a broad, southeastward flow across the basin. 26

27. LOM: Δd
(CI = 0.05 cm)
Surface geostrophic (baroclinic) currents extend southeastward across the SIO, with a richer meridional structure than in the LCS solution.
1) Pattern of Δd similar to that of LCS model, but with more “defined” structure, due to upwelling/downwelling areas being localized.
The curved bands in the southern oceans result from a southward (northward) shift of the ACC in the IO (PO). 27

28. LOM: SICC
The circulation is more complex in LOM because vertical diffusion (across-layer transfer) occurs primarily where layer thicknesses become too thin (upwelling) or too thick (subduction).
Δhv1+2
The South Indian Countercurrent extends across the basin along 25°S and flows to the southeast corner of the basin. 28

29. LOM: SICC
There is flow from the IO to the PO driven by eastward subsurface currents (Tsuchiya Jets) in the PO.
Δhv3
The SICC subducts off southwest and south of Australia, returns to the coast of Madagascar, and joins the ACC. Eventually it flows into the Pacific in layer 3.
So, in contrast to the LCS model, much of the downwelling is located southwest and south of Australia, rather than spread throughout the IO. This localization is why the eastward flow forms a narrow jet in LOM, in contrast to the broad flow in the LCS model.
Water can also mix downward into layer 4 along the flanks of the ACC.
Subduction in the southeast IO and south of Australia drives the surface South Indian Countercurrent and a compensating subsurface westward flow along 25°S. 29

30. COCO: Δd
Surface geostrophic (baroclinic) currents extend southeastward across the southern IO, with richer meridional structure than in the LCS solution.
Pattern of Δd is remarkably similar to that of LCS model, but with more “defined” structure, due to upwelling/downwelling areas being localized.
Subduction and convective overturning in the southeast IO drives a surface South Indian Countercurrent along 25°S.

31. COCO: SICC T u, T, open u, T, closed
State clearly that this plot is NOT a difference field.
There is an eastward countercurrent overlying westward flow from 20−25°S. It extends from Madagascar to a region of convective overturning off Southwest Australia. It is much stronger when the Indonesian passages are open.

32. Pacific Ocean Great Barrier Reef Undercurrent
How does the IT impact the South Pacific? 32

33. COCO: Δψ
Barotropic flow field circulates around the southern IO and flows northward along the east Australian coast, with no significant currents in the interior of the Pacific
The barotropic transport around Australia strengthens the northward flow along the east coast of Australia.
What is the impact of this current on the SEC bifurcation latitude? It shifts it southward.

34. COCO: SEC bifurcation latitude
v, obs.
The observed SEC bifurcation shifts poleward with depth from about 16°S to 22°S. The deep northward flow within this latitude range is known as the Great Barrier Reef Undercurrent (GBRUC).
v, open
A similar shift occurs in COCO but not in COCO´, a consequence of the strong northward flow along the Australian coast associated with the IT. This result suggests that the IT is the cause of the GBRUC.
v, closed

35. How does the IT impact the tropical Pacific?
Pacific Ocean
Tsuchiya Jets (layer 3)
How does the IT impact the tropical Pacific?

36. LOM: Tsuchiya Jets hv3, open
With open IT passages, eastward currents in layer 3 extend from the western boundary to off-equatorial upwelling regions in the eastern ocean, the model’s Tsuchiya Jets (TJs). The IT drains enough water from layers 1 and 2 that upwelling extends into layer 3.

37. LOM: Tsuchiya Jets hv3, closed
Based on a similar solution to a 4½-layer model, McCreary et al. (2002) concluded that the IT was necessary for the existence of the TJs, but …
With closed passages, the TJs are essentially eliminated. In this case, layers 1 and 2 are thicker, preventing much of the upwelling from extending to layer 3. In addition, the NGCUC reverses to flow southeastward to about 9˚S, so that southern-hemisphere water never reaches the equator.

38. COCO: Tsuchiya Jets u, T, open u, T, closed 1oC warmer
1) A better interpretation of the McCreary et al. (2002) results, then, is that its limited vertical resolution caused the disappearance of the TJs: Instead of just shifting slightly upward, the TJs had to shift up into layer 2, where they were overwhelmed by the stronger thermocline flows and hence “disappeared.”
1oC warmer
With closed passages, the TJ is somewhat shallower with its core 1°C warmer, since less upper-ocean water is drained from the basin. Its strength is only slightly weakened, suggesting that the TJs are supplied primarily by an overturning cell within the Pacific basin.

39. How does the IT impact the North Pacific?
Pacific Ocean
AAIW (layer 4)
How does the IT impact the North Pacific?

40. LOM: Flow of AAIW into NP
Δhv4
hv4, open
The difference field misrepresents pathways by which water actually flows into the North Pacific. It flows through the tropics by a circuitous route, due to deep, eddy-driven circulations associated with the Hawaii Lee Countercurrent. The window circulation is reversed by the Pacific’s wind-driven, double-gyre (STC and SPG). So, water enters the subpolar ocean along the boundary between the gyres.
Δhv4
With closed passages, no AAIW flows into the northern hemisphere, indicating that the IT is the cause of this flow.
The transport of the NGCUC in layer 4 (AAIW) is 3.5 SV. Of this amount, 2.7 Sv flows directly out of the Pacific into the Indian Ocean. The remaining 0.8 Sv flows into the far North Pacific. Its path through the tropics is not clear. It enters the subpolar ocean through a “baroclinic window” (Pedlosky, 1984), and upwells into the shallower layers there via Ekman suction. 40

41. COCO: Flow of AAIW into NP
hv4, open
The difference field misrepresents pathways by which water actually flows into the North Pacific. It again flows through the tropics by a circuitous route, first flowing eastward near 7°N and then westward in the STG. The window circulation is reversed by the Pacific’s wind-driven, double-gyre (STC and SPG). So, water enters the subpolar ocean along the gyre boundaries or near the eastern boundary.
Δhv4
As for LOM, with closed passages no AAIW flows into the northern hemisphere, indicating that the IT is the cause of this flow.
The NGCUC transport in layer 4 (AAIW) is 2.5 SV. Of this amount, 1.3 Sv flows directly into the Indian Ocean. The remaining 1.2 Sv flows into the North Pacific. It flows northward in a western-boundary current, and circulates about a deep part of the NP Subtropical Gyre. As in Solution ΔLOM, it then enters the subpolar ocean through a “baroclinic window,” eventually upwelling into the shallower layers there. 41

42. Summary

43. In the interiors of the Pacific and Indian Oceans, circulations associated with the IT are generated by the radiation and decay of baroclinic waves. As a consequence, subsurface currents are directed opposite to their surface counterparts. Details of the circulations are sensitive to the nature of diapycnal mixing.
The IT is split into near-surface and deep cores by baroclinic currents generated in the interior Pacific (EUC and TJs). ITF source waters come from the north (south) in the shallow (deep) core, the former due to the near-surface circulation driven by Pacific winds or to inertial overshoot.
The SICC is generated by subduction and/or convection near Southwest Australia. The ITF strengthens the SICC considerably.
The IT enhances northward flow along the east coast of Australia, generating the GBRUC.
The IT provides all (LOM) or some (GCMs) of the thermostad water that flows across the Pacific in the TJs to upwell in the eastern ocean.
The IT is the reason why AAIW flows into the North Pacific, eventually to upwell in the Subpolar Gyre.

45. LOM: Δh1+2
(CI = 10 m)
The thermocline depth (h1 + h2) deepens by more than 100 m off the west coast of Australia.

48. …particularly in the South Pacific from 20S o 5S.Δd
Surface geostrophic (baroclinic) currents extend westward and equatorward across the PO…
…particularly in the South Pacific from 20S o 5S.

49. Sea-surface temperature

50. LOM: Flow of AAIW into NP
Δhv4
With closed passages, no AAIW flows into the northern hemisphere, indicating that the IT is the cause of this flow.
The transport of the NGCUC in layer 4 (AAIW) is 3.5 SV. Of this amount, 2.7 Sv flows directly out of the Pacific into the Indian Ocean. The remaining 0.8 Sv flows into the far North Pacific. Its path through the tropics is not clear. It enters the subpolar ocean through a “baroclinic window” (Pedlosky, 1984), and upwells into the shallower layers there via Ekman suction. 50

51. COCO: Flow of AAIW into NP
Δhv4
As for LOM, with closed passages no AAIW flows into the northern hemisphere, indicating that the IT is the cause of this flow.
The NGCUC transport in layer 4 (AAIW) is 2.5 SV. Of this amount, 1.3 Sv flows directly into the Indian Ocean. The remaining 1.2 Sv flows into the North Pacific. It flows northward in a western-boundary current, and circulates about a deep part of the NP Subtropical Gyre. As in Solution ΔLOM, it then enters the subpolar ocean through a “baroclinic window,” eventually upwelling into the shallower layers there. 51

52. Dynamics Indonesian Seas Pacific Ocean
Because of the ITF, in the IO sea level rises, there are anomalous south-westward surface (northwestward subsurface) baroclinic currents across the interior of the southern IO, and downwelling. Conversely, in the PO sea level lowers, there are anomalous westward and equatorward, surface (eastward and poleward, subsurface) interior currents, and upwelling. Details of the circulations depend on the nature of diapycnal mixing.
Indonesian Seas
The ITF is split into near-surface and deep cores by baroclinic currents generated in the interior Pacific (EUC and TJs). ITF source waters come from the north (south) in the shallow (deep) core, the former due to the near-surface circulation driven by Pacific winds or to inertial overshoot.
Pacific Ocean
In LOM, the IT generates TJs by thinning layers 1 & 2 until upwelling can extend to layer 3; in COCO, the IT shallows the TJs.

53. 1) Pacific circulations associated with the IT are generated by the radiation and decay of baroclinic waves. As a consequence, subsurface currents are directed opposite to their surface counterparts.
2) The structure of the interior flow field depends on the types of diffusion present in the model, namely, vertical mixing (LCS model, GCMs), upwelling and subduction (LOM, GCMs), and convection (GCMs).
3) The IT provides some (GCMs) or all (LOM) of the thermostad water that upwells off Peru and in the Costa Rica dome.
4) The IT is the reason that water in the density range of AAIW flows from the South Pacific to the North Pacific Subpolar Gyre.

54. What sets the strength of the IT?
Godfrey’s Island Rule, and its modifications
2) Why is most of the IT surface trapped in the upper 400 m, with indications of a second deep core?
3) Why does the near-surface flow come from the North Pacific, and the deep flow from the South Pacific?
4) Why does the South-Pacific inflow extend to intermediate depths?
5) What processes account for remote impacts of the IT in the Indian and Pacific Oceans?
Wave propagation, and their damping due to diffusion, upwelling, or convection
6) In particular, what processes transform the warm, shallow IT to deep, cool SP inflow, and vice versa
7) What is the impact of the IT on subthermocline circulations in the Pacific, particularly on the flow of thermostad water and AAIW?