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The Bottom Boundary Layer in the Eastern Tropical Pacific

S. P. HayesNOAA Pacific Marine Environmental Laboratory, Seattle, Washington 98105

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Abstract

Vertical and horizontal structure of near-bottom currents at two locations in the eastern tropical Pacific (9°26′N, 151°17′W; 14°38′N, 125°29′W) have been studied. Low-frequency currents at these sites, located in a region of abyssal hills, increased between 500 m and 50 m above bottom and had small horizontal scale. Below 50 m frictional boundary-layer effects which were consistent with a simple, steady-state Ekman-like layer were apparent. Total veering within the boundary layer was, 10° counterclockwise (looking down) at both locations. High-frequency internal wave motions were consistent with a modified Garrelt and Munk internal wave spectrum. Energy correspondence calculations for several high-frequency bands showed some evidence for benthic internal wave generation by means of mean flow topography interaction. At the western site the near-inertial energy-time dependence and near-bottom enhancement both indicated local production in this band. Below 50 m frictional effects were again important. The observations showed veering and attenuation which depended on frequency and polarization in a manner consistent with time-dependent Ekman dynamics.

Abstract

Vertical and horizontal structure of near-bottom currents at two locations in the eastern tropical Pacific (9°26′N, 151°17′W; 14°38′N, 125°29′W) have been studied. Low-frequency currents at these sites, located in a region of abyssal hills, increased between 500 m and 50 m above bottom and had small horizontal scale. Below 50 m frictional boundary-layer effects which were consistent with a simple, steady-state Ekman-like layer were apparent. Total veering within the boundary layer was, 10° counterclockwise (looking down) at both locations. High-frequency internal wave motions were consistent with a modified Garrelt and Munk internal wave spectrum. Energy correspondence calculations for several high-frequency bands showed some evidence for benthic internal wave generation by means of mean flow topography interaction. At the western site the near-inertial energy-time dependence and near-bottom enhancement both indicated local production in this band. Below 50 m frictional effects were again important. The observations showed veering and attenuation which depended on frequency and polarization in a manner consistent with time-dependent Ekman dynamics.

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