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The Influence of Propagating Waves on Cross-Stream Excursions

M. Susan LozierOcean Sciences Program, Duke University, Durham, North Carolina

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Timothy J. BoldDepartment of Mechanical Engineering, Duke University, Durham, North Carolina

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Amy S. BowerWoods Hole Oceanographic Institution, Woods Hole, Massachusetts

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Abstract

A kinematic model is developed to examine the relationship between meander propagation and Lagrangian pressure change within a meandering jet. Basically, the model equates changes in pressure along the path of a water parcel with the cross-stream motion of a parcel in a reference frame moving with the meander. The model is tested by combining isopycnal float data from the Gulf Stream with contemporaneous meander phase speed observations from satellite infrared images. Time series of pressure changes along individual float trajectories show a qualitative trend for the amplitude of pressure changes to generally increase in response to large phase speeds. However, the model suggests that the pressure change following a fluid parcel is related to the vector difference between the velocity and phase speed vectors, not just the magnitude of the phase speed. This is confirmed by the data analysis, which shows that Lagrangian pressure changes are more highly correlated with cross-stream flow when both the zonal and meridional components of the meander propagation are included in the kinematic model. Approximately 90% of the variability associated with the floats’ pressure changes can he accounted for by cross-stream flow using this kinematic formulation.

Abstract

A kinematic model is developed to examine the relationship between meander propagation and Lagrangian pressure change within a meandering jet. Basically, the model equates changes in pressure along the path of a water parcel with the cross-stream motion of a parcel in a reference frame moving with the meander. The model is tested by combining isopycnal float data from the Gulf Stream with contemporaneous meander phase speed observations from satellite infrared images. Time series of pressure changes along individual float trajectories show a qualitative trend for the amplitude of pressure changes to generally increase in response to large phase speeds. However, the model suggests that the pressure change following a fluid parcel is related to the vector difference between the velocity and phase speed vectors, not just the magnitude of the phase speed. This is confirmed by the data analysis, which shows that Lagrangian pressure changes are more highly correlated with cross-stream flow when both the zonal and meridional components of the meander propagation are included in the kinematic model. Approximately 90% of the variability associated with the floats’ pressure changes can he accounted for by cross-stream flow using this kinematic formulation.

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