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A Comparison of Geostrophic Velocities and Profiling ADCP Measurements in the Iberian Basin

H-H. HinrichsenInstitut für Meereskunde, Kiel, Germany

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A. LehmannInstitut für Meereskunde, Kiel, Germany

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Abstract

During a hydrographic survey within the Iberian Basin and the Gulf of Cadiz, a combined CTD-ADCP profiling system is used to resolve the mesoscale mass distribution and flow fields of the Mediterranean Water tongue. Generally, the geostrophic flow pattern and the shear field of the ADCP velocities are in good agreement, except in near-coastal regions where strong ageostrophic velocity components can be expected. The error of the absolute velocity strongly depends on the uncertainty of the global positioning system and the duration of a CTD-ADCP cast, whereas the accuracy of the shear velocities does not exceed the inherent instrumental error of 1 cm s−1. Similar estimates of the geostrophic currents yield a strong dependence on the geographical latitude and the distance between two CTD locations used for the application of the dynamic method. Effects of internal tide phenomena on geostrophy are considered by vertical displacements of isopycnals.

Abstract

During a hydrographic survey within the Iberian Basin and the Gulf of Cadiz, a combined CTD-ADCP profiling system is used to resolve the mesoscale mass distribution and flow fields of the Mediterranean Water tongue. Generally, the geostrophic flow pattern and the shear field of the ADCP velocities are in good agreement, except in near-coastal regions where strong ageostrophic velocity components can be expected. The error of the absolute velocity strongly depends on the uncertainty of the global positioning system and the duration of a CTD-ADCP cast, whereas the accuracy of the shear velocities does not exceed the inherent instrumental error of 1 cm s−1. Similar estimates of the geostrophic currents yield a strong dependence on the geographical latitude and the distance between two CTD locations used for the application of the dynamic method. Effects of internal tide phenomena on geostrophy are considered by vertical displacements of isopycnals.

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