Near-Inertial Wave Propagation into the Pycnocline during Ocean Storms: Observations and Model Comparison

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  • 1 College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
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Abstract

Observations of near-inertial oscillations collected during the Ocean Storms Experiment in the northeast Pacific Ocean are compared with results from a linear, numerical model on a β plane, developed by Zervakis and Levine. A slab mixed layer model, forced by the observed wind time series, is used to identify three isolated events of local generation in October, January, and March for detailed analysis. Synoptic storm track maps are used to estimate the initial horizontal wavenumber of the mixed layer currents that are used as initial conditions to the modal. A comparison of the modal with the observed currents reveals some differences and similarities. Overall the January and March events are better represented by the model than the October event. The timescale of the initiation of vertical propagation of energy from the mixed layer occurs almost immediately in October rather than after 8 days in January and March-this difference cannot be explained by the model. The observed vertical and temporal structure indicates that the near-Inertial energy propagated as a “beam” of energy through the pycnocline, especially in October. In the model the wave energy appears to accumulate at the top of the pycnocline. Physical processes that might be responsible for the deficiency of the model are discussed.

Abstract

Observations of near-inertial oscillations collected during the Ocean Storms Experiment in the northeast Pacific Ocean are compared with results from a linear, numerical model on a β plane, developed by Zervakis and Levine. A slab mixed layer model, forced by the observed wind time series, is used to identify three isolated events of local generation in October, January, and March for detailed analysis. Synoptic storm track maps are used to estimate the initial horizontal wavenumber of the mixed layer currents that are used as initial conditions to the modal. A comparison of the modal with the observed currents reveals some differences and similarities. Overall the January and March events are better represented by the model than the October event. The timescale of the initiation of vertical propagation of energy from the mixed layer occurs almost immediately in October rather than after 8 days in January and March-this difference cannot be explained by the model. The observed vertical and temporal structure indicates that the near-Inertial energy propagated as a “beam” of energy through the pycnocline, especially in October. In the model the wave energy appears to accumulate at the top of the pycnocline. Physical processes that might be responsible for the deficiency of the model are discussed.

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