Propagation of Gulf Stream Meanders between 74° and 70°W

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  • 1 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts
  • | 2 Graduate School of Oceanography. University of Rhode Island, Narragansett, Rhode Island
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Abstract

Positions of the Gulf Stream path from 74° to 45°W were obtained from satellite infrared images for the period of April 1982–December 1989. The propagation of meanders between 74° and 70°W was studied through spectral analysis in wavenumber-frequency space, empirical orthogonal function analysis in time and frequency domains, and direct measurements of individual meander properties. Progressive meanders are found to have a broad range of periods from days to years, and wavelengths from about 200 to 1100 km. Good agreement is found between the satellite and Inverted Echo Sounder data for short-period (<80 days) progressive propagation. Retrogressive meanders with wavelengths longer than 1100 km are found to coexist with progressive ones at periods longer than 4 months. The empirical dispersion relation is in qualitative agreement with the linear prediction of a recent equivalent-barotropic,β-plane thin-jet model, the comparison also suggests that topographic β may need to be considered in order to account for the magnitudes of observed retrogressive phase speeds. Amplitude dependence of propagation is observed. with the phase speed decreasing as the amplitude increases. Standing meanders are observed at periods when both progressive and retrogressive propagation are present; their wavelengths fall between those of oppositely traveling meanders. These standing meanders are responsible for the standing wave pattern of the path envelope between Cape Hatteras and 69°W It is argued that they are formed by near-stationary meanders of a similar wavelength but different amplitudes propagating in opposite directions as a result of the combined amplitude-dependent and β effect.

Abstract

Positions of the Gulf Stream path from 74° to 45°W were obtained from satellite infrared images for the period of April 1982–December 1989. The propagation of meanders between 74° and 70°W was studied through spectral analysis in wavenumber-frequency space, empirical orthogonal function analysis in time and frequency domains, and direct measurements of individual meander properties. Progressive meanders are found to have a broad range of periods from days to years, and wavelengths from about 200 to 1100 km. Good agreement is found between the satellite and Inverted Echo Sounder data for short-period (<80 days) progressive propagation. Retrogressive meanders with wavelengths longer than 1100 km are found to coexist with progressive ones at periods longer than 4 months. The empirical dispersion relation is in qualitative agreement with the linear prediction of a recent equivalent-barotropic,β-plane thin-jet model, the comparison also suggests that topographic β may need to be considered in order to account for the magnitudes of observed retrogressive phase speeds. Amplitude dependence of propagation is observed. with the phase speed decreasing as the amplitude increases. Standing meanders are observed at periods when both progressive and retrogressive propagation are present; their wavelengths fall between those of oppositely traveling meanders. These standing meanders are responsible for the standing wave pattern of the path envelope between Cape Hatteras and 69°W It is argued that they are formed by near-stationary meanders of a similar wavelength but different amplitudes propagating in opposite directions as a result of the combined amplitude-dependent and β effect.

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