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A Simulation of the Abyssal Circulation in the North Pacific Ocean. Part I: Flow Field and Comparison with Observations

Hiroshi IshizakiOceanographic Research Department, Meteorological Research Institute, Tsukuba, Japan

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Abstract

A simulation was made of the abyssal circulation in the North Pacific Ocean. The model covers the whole Pacific, has realistic coastal geometry and bottom topography, and is driven by the annual mean surface wind stress and the annual mean differential heating at the surface and the southern boundary. About 6.5 Sv (Sv ≡ 106 m3 s−1) of bottom water crosses the equator from the South to the North Pacific below 3500 m and rises there, with 2.8 Sv of the 6.5 Sv returning to the South Pacific in the layer between 1750 and 3250 m. The abyssal water below 1750 m is divided into three layers: the upper deep layer (1750–3250 m), the lower deep layer (3250–4250 m), and the bottom layer (below 4250 m), based on the large-scale horizontal circulation pattern. In the bottom layer, the western boundary current flows to the north without any stagnation point, and the interior flow is essentially zonal and eastward, especially over the gentle slope of the western flank of the East Pacific Rise. In the upper and lower deep layers, on the other hand, a single anticyclonic gyre is dominant over the whole North Pacific excluding the Philippine Sea. In particular, the horizontal circulation pattern in the upper deep layer can be regarded as a reversed pattern of the Stommel-Arons circulation, driven by the outflux from the North to the South Pacific in the layer and consequent vertical shrinking of the water column.

The present results are compared with recent observations including deep-water property distributions, trans-Pacific hydrographic data analyses, and deep current meter records. There is a general similarity between the simulation and observations, with some discrepancies, particularly in the equatorial regions.

Abstract

A simulation was made of the abyssal circulation in the North Pacific Ocean. The model covers the whole Pacific, has realistic coastal geometry and bottom topography, and is driven by the annual mean surface wind stress and the annual mean differential heating at the surface and the southern boundary. About 6.5 Sv (Sv ≡ 106 m3 s−1) of bottom water crosses the equator from the South to the North Pacific below 3500 m and rises there, with 2.8 Sv of the 6.5 Sv returning to the South Pacific in the layer between 1750 and 3250 m. The abyssal water below 1750 m is divided into three layers: the upper deep layer (1750–3250 m), the lower deep layer (3250–4250 m), and the bottom layer (below 4250 m), based on the large-scale horizontal circulation pattern. In the bottom layer, the western boundary current flows to the north without any stagnation point, and the interior flow is essentially zonal and eastward, especially over the gentle slope of the western flank of the East Pacific Rise. In the upper and lower deep layers, on the other hand, a single anticyclonic gyre is dominant over the whole North Pacific excluding the Philippine Sea. In particular, the horizontal circulation pattern in the upper deep layer can be regarded as a reversed pattern of the Stommel-Arons circulation, driven by the outflux from the North to the South Pacific in the layer and consequent vertical shrinking of the water column.

The present results are compared with recent observations including deep-water property distributions, trans-Pacific hydrographic data analyses, and deep current meter records. There is a general similarity between the simulation and observations, with some discrepancies, particularly in the equatorial regions.

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