Pacific Ocean western boundary currents and the interlinked equatorial Pacific circulation system were among the first currents of these types to be explored by pioneering oceanographers. The widely accepted but poorly quantified importance of these currents-in processes such as the El Niño/Southern Oscillation, the Pacific Decadal Oscillation and the Indonesian Throughflow-has triggered renewed interest. Ongoing efforts are seeking to understand the heat and mass balances of the equatorial Pacific, and possible changes associated with greenhouse-gas-induced climate change. Only a concerted international effort will close the observational, theoretical and technical gaps currently limiting a robust answer to these elusive questions.

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Intraseasonal oscillations in sea level, sea surface temperature, and upper ocean flow field have recently been observed in various locations surrounding the Indonesian seas. While the observed oscillations at these locations have similar wave periods ranging from 30 to 85 days, their forcing mechanisms can involve different dynamic processes. In order to clarify the dynamic processes essential for the observed intraseasonal signals, the authors adopted in this study a fine-resolution 1½-layer reduced-gravity model and carried out a series of model experiments by varying coastline geometry and surface wind forcing. From these carefully designed experiments, they show that the intense 50-day oscillations observed at the entrance of Celebes Sea are a result of Rossby wave resonance in which the frequency of cyclonic eddy shedding by the retroflecting Mindanao Current matches that of the gravest Rossby mode of the semi-enclosed Celebes Sea basin. These 50-day oscillations of the Celebes Sea have a large impact on the throughflow in the Makassar Strait and Banda Sea, but do not contribute significantly to the throughflow changes in the Lombok, Ombai, and Timor Straits.The observed intraseasonal signals along the Sumatra/Java coasts in the eastern Indian Ocean are dominated by oscillations with wave periods of 50 and 85 days. The origin of these wave signals can be traced back to the central equatorial Indian Ocean where the surface zonal wind fluctuates intraseasonally with the same wave periods. The remotely induced coastal Kelvin waves along the Sumatra/Java coasts strongly influence the Lombok Strait, but exert no direct influence upon the Ombai and Timor Straits farther to the east; the gap of the Lombok Strait is found to conduit the Kelvin wave signals effectively into the Makassar Strait and the Banda Sea. The intraseasonal signals observed in the Timor Passage have a dominant wave period of 30-35 days. The model simulation further suggests the presence of a second spectral peak around 85 days. Both of these intraseasonal signals are attributable to the local, along-archipelago wind near the Timor Passage.

Subthermocline circulation in the tropical North Pacific Ocean (2°N–30°N) is investigated using profiling float temperature‐salinity data from the International Argo and the Origins of the Kuroshio and Mindanao Current (OKMC) projects. Three well‐defined eastward jets are detected beneath the wind‐driven, westward flowing North Equatorial Current. Dubbed the North Equatorial Undercurrent (NEUC) jets, these subthermocline jets have a typical core velocity of 2–5 cms−1 and are spatially coherent from the western boundary to about 120°W across the North Pacific basin. Centered around 9°N, 13°N, and 18°N in the western basin, the NEUC jet cores tend to migrate northward by ∼4° in the eastern basin. Vertically, the cores of the southern, central, and northern NEUC jets reside on the 26.9, 27.2, and 27.3 σθsurfaces, respectively, and they tend to shoal to lighter density surfaces, by about 0.2 σθ, as the jets progress eastward.

[1] Mooring observations were conducted from October 1999 to July 2002 near the east coast of Mindanao Island, the Philippines, (6°50 0 N, 126°43 0 E) to observe current variability at the axis of the Mindanao Current (MC). The MC was a strong current with a subsurface velocity maximum exceeding 1.3 m s À1 at approximately 100 m depth. The MC flows shallower than 700 m, and there was no evidence of a steady northward current (the Mindanao Undercurrent) at the study location. Compared with the large average velocity, MC variability was low (standard deviation <0.2 m s À1 for all directions). All the observed interannual, seasonal, and intraseasonal variations in the MC were of comparable amplitude. The MC was strong during boreal summers and during the onset of the 2002 -03 El Niño. The core velocity of the MC at approximately 100 m was correlated with the sea level difference between Cebu, Philippines and Malakal, Palau. Citation: Kashino, Y.,