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A persistent (two-year mean), equatorward, Pacific DWBC was found inshore of the Japan Trench near 35°N by Hallock and Teague (1995) as a result of the in situ observational component of the Kuroshio Extension Regional Experiment (KERE). This flow extends from the bottom up to at least 2000 m and exhibits variability on a range of time scales. Other observations indicate considerable eddy/meander activity in the region (Mitchell et et al., 1995; Teague et al., 1994). Above the Japan Trench, deep mean current is generally northward. Modeling studies have indicated strong correlations between mean Kuroshio path with abyssal currents and topography.
In the Atlantic, the DWBC is relatively intense (due to a major source of deep water in polar regions) and has been shown to be quite important in the physics of Gulf Stream separation (Thompson and Schmitz, 1989). The reason for the existence of the Pacific DWBC is still somewhat unclear; observations are generally consistent with predictions of the Stommel and Arons (1960) theory of the thermohaline circulation but NRL model results suggest eddy-driving, through baroclinic instability of the Kuroshio, as the primary mechanism (Hurlburt et al, 1995). These competing hypotheses are not mutually exclusive, however.
In the region of the KERE observations, which is analogous to the Cape Hatteras region for the Gulf Stream, flows strongly interact with topography and each other. There are important differences between these two regions, however; while the continental margin turns eastward north of Cape Hatteras in the Atlantic, it continues generally northward from Japan until encountering the Aleutians. One such interaction is suggested in preliminary analyses of in situ data which show a correlation between a southward excursion of the Kuroshio axis near the coast with an increase in southward transport of the Pacific DWBC along the continental slope. Furthermore, TOPEX altimetry and infrared imagery indicate the possible interaction of a warm ring with the Kuroshio during the observed southward shift of the current. Pickart (1994) and Pickhart et al. (1990) describe characteristics of the Atlantic DWBC near Cape Hatteras. They find that for long (longer than 100 days) periods, meanders of the Gulf Stream force changes in the DWBC.
Using the KERE data sets and other related existing results, we hope to investigate the interrelationship between Kuroshio fluctuations (e.g. meanders, eddy interactions) and those of the the Pacific DWBC and other deep flows in the region where the Kuroshio turns eastward and separates from the coast near 35°N. In particular, we will attempt to determine the source of large-amplitude changes in Kuroshio position, will estimate the effects of these changes on deep transports, and will estimate eddy-stress effects of deep, fluctuating velocities.
Possible hypotheses to be considered are as follows:
References
Hallock, Z. R. and W. J. Teague. 1995. Evidence for a Pacific Deep Western Boundary Current. J. Geophys. Res., 101(C3): 6617-6624.
Hurlburt, H. E., A. J. Wallcraft, W. J. Schmitz, Jr., P. J. Hogan, and E. J. Metzger. 1995. Dynamics of the Kuroshio/Oyashio current system using eddy-resolving models of the North Pacific Ocean. J. Geophys. Res., 101: 941-976.
Mitchell, J. L., W. J. Teague, G. A. Jacobs, and H. E. Hurlburt. 1995. Kuroshio Extension Dynamics from Satellite Altimetry and a Model Simulation. J. Geophys. Res., 101: 1045-1058.
Pickart, R. S. 1994. Interaction of the Gulf Stream and Deep Western Boundary Current where they cross. J. Geophys. Res., 99(C12): 25,155-25,164.
Pickart, R. S. and D. R. Watts. 1990. Deep western boundary current variability at Cape Hatteras. J. Mar. Res, 48: 765-791.
Stommel, H. and A. B. Arons. 1960. On the abyssal circulation of the world ocean. I. Stationary planetary flow patterns on a sphere. Deep-Sea Res., 6: 140-154.
Teague, W. J., A. M. Shiller, and Z. R. Hallock. 1994. Hydrographic Section Across the Kuroshio near 35°N, 143°E. J. Geophys. Res., 99(C4): 7639-7650.
Thompson, J. D. and W. J. Schmitz. 1989. A limited-area model of the Gulf Stream: design and initial experiments. J. Phys. Oceanogr., 19: 179-814.
by Z. R. Hallock, W. J. Teague, G. A. Jacobs, H. E. Hurlburt, and E. R. Fillenbaum
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