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Vertical Structure of the Baroclinic Tides in the Central North Pacific Subtropical Gyre

Stephen M. ChiswellJoint Institute for Marine and Atmospheric Research, University of Hawaii, Honolulu, Hawaii

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Abstract

Cruises are made monthly to the World Ocean Circulation Experiment deep-water station, about 100 km north of Oahu, Hawaii. During these cruises, the principal causes of variability in dynamic height are the internal tides having a range about 30% of the annual range in dynamic height.

The internal tides have peak-to-peak vertical displacements of up to 30 dbar but show little vertical coherence. At the diurnal frequencies modal fits typically require 6–8 baroclinic modes to account for 90% of the variance, suggesting that the diurnal tide should not be described in terms of dynamic modes. The semidiurnal tide has about two to three times the amplitude of the diurnal tide and shows more vertical phase coherence, but still requires three or four modes to describe it. Generally, the dominant mode is the second or third mode.

Abstract

Cruises are made monthly to the World Ocean Circulation Experiment deep-water station, about 100 km north of Oahu, Hawaii. During these cruises, the principal causes of variability in dynamic height are the internal tides having a range about 30% of the annual range in dynamic height.

The internal tides have peak-to-peak vertical displacements of up to 30 dbar but show little vertical coherence. At the diurnal frequencies modal fits typically require 6–8 baroclinic modes to account for 90% of the variance, suggesting that the diurnal tide should not be described in terms of dynamic modes. The semidiurnal tide has about two to three times the amplitude of the diurnal tide and shows more vertical phase coherence, but still requires three or four modes to describe it. Generally, the dominant mode is the second or third mode.

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