Circulation within the Ocean Storms Area Located in the Northeast Pacific Ocean Determined by Inverse Methods

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  • 1 Department of Oceanography, University of British Columbia, Vancouver, British Columbia, Canada
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Abstract

An inverse model was applied to hydrographic data obtained from a cruise in the autumn of 1987 in a small area (300 × 250 km) in the northeast Pacific Ocean. The inverse model used geostrophy and a linear β-plane vorticity equation as dynamical constraints. The conservation of mass and the steady-state advection–diffusion equations for temperature and salinity were used to form a set of equations from which the reference level velocities and mixing terms were determined. Additional constraints were included in the model by forcing the horizontal velocity from the model to be consistent with bouy data from the near surface.

The vertical mixing coefficients determined by the model increased from zero at 150 m to 14 cm2 s−1 at 1500 m. The horizontal diffusivity displayed a minimum at 500 m of 1000 m2 s−1 and increased to 5300 m2 s−1 at 150 m. A middepth maximum of 6000 m2 s−1 was observed at 900 m before decreasing to zero at 1500 m. The calculated vertical velocities were weak functions of depth changing by less than 3.0 × 10−6 m s−1 between 150 m and 1500 m, showing the horizontal velocities to he nearly nondivergent.

The geostrophic flow field determined from the inverse model was generally smooth, exhibiting well-defined flow features. The horizontal flow did not indicate a depth of no motion in the study area. The comparison of a 7-day average of current meter observations with inverse velocities showed that the two velocity measurements were consistent at 500 m. The difference between the two velocities increased as one moved upward from 500 m and downward to 1000 m. The increases in the velocity differences agreed with the calculated horizontal diffusivities, which implied enhanced eddy activity in the upper ocean and at middepths.

Abstract

An inverse model was applied to hydrographic data obtained from a cruise in the autumn of 1987 in a small area (300 × 250 km) in the northeast Pacific Ocean. The inverse model used geostrophy and a linear β-plane vorticity equation as dynamical constraints. The conservation of mass and the steady-state advection–diffusion equations for temperature and salinity were used to form a set of equations from which the reference level velocities and mixing terms were determined. Additional constraints were included in the model by forcing the horizontal velocity from the model to be consistent with bouy data from the near surface.

The vertical mixing coefficients determined by the model increased from zero at 150 m to 14 cm2 s−1 at 1500 m. The horizontal diffusivity displayed a minimum at 500 m of 1000 m2 s−1 and increased to 5300 m2 s−1 at 150 m. A middepth maximum of 6000 m2 s−1 was observed at 900 m before decreasing to zero at 1500 m. The calculated vertical velocities were weak functions of depth changing by less than 3.0 × 10−6 m s−1 between 150 m and 1500 m, showing the horizontal velocities to he nearly nondivergent.

The geostrophic flow field determined from the inverse model was generally smooth, exhibiting well-defined flow features. The horizontal flow did not indicate a depth of no motion in the study area. The comparison of a 7-day average of current meter observations with inverse velocities showed that the two velocity measurements were consistent at 500 m. The difference between the two velocities increased as one moved upward from 500 m and downward to 1000 m. The increases in the velocity differences agreed with the calculated horizontal diffusivities, which implied enhanced eddy activity in the upper ocean and at middepths.

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