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The Role of Vertical Motion in the Heat Budget of the Upper Northeastern Pacific Ocean

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  • 1 Hawaii Institute of Geophysics and Department of Oceanography, University of Hawaii, Honolulu 96822
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Abstract

A study of the heat budget of the upper northeastern Pacific Ocean demonstrates the importance of heat changes due to vertical motion. Bathythermograph observations are used to form time series of monthly average thermal structure at ocean weather station November (30°N, 140°W) and various 5° and 2° quadrangles between California and Hawaii. These time series are first used to explore correlations between heat content in a 250 m thick layer and the depth of the 14°C isotherm. High negative correlations between these quantities suggest that vertical motion at 250 m, indicated by the fluctuations of the 14°C isotherm, must play a significant role in altering the heat content of the upper layer. A heat budget equation is derived that includes the heat changes due to vertical motion. At all test locations, correlations between terms show that a stronger relationship exists between surface heat exchange and heat content change when the heat changes due to vertical motion are included. The mean square difference between surface heat exchange and heat content change is computed with and without heat changes due to vertical motion. The ratio of these differences shows about a 50% improvement when heat changes due to vertical motion are included.

Abstract

A study of the heat budget of the upper northeastern Pacific Ocean demonstrates the importance of heat changes due to vertical motion. Bathythermograph observations are used to form time series of monthly average thermal structure at ocean weather station November (30°N, 140°W) and various 5° and 2° quadrangles between California and Hawaii. These time series are first used to explore correlations between heat content in a 250 m thick layer and the depth of the 14°C isotherm. High negative correlations between these quantities suggest that vertical motion at 250 m, indicated by the fluctuations of the 14°C isotherm, must play a significant role in altering the heat content of the upper layer. A heat budget equation is derived that includes the heat changes due to vertical motion. At all test locations, correlations between terms show that a stronger relationship exists between surface heat exchange and heat content change when the heat changes due to vertical motion are included. The mean square difference between surface heat exchange and heat content change is computed with and without heat changes due to vertical motion. The ratio of these differences shows about a 50% improvement when heat changes due to vertical motion are included.

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