On the mesoscale variability observed in the North Atlantic by satellite altimeters

Abstract

Soviet altimetry data, disclosed recently, are applied to describe mesoscale sea-level variability in the North Atlantic. The method of satellite data processing is presented and possible errors are estimated. Variations of sea surface heights measured by several altimeters in non-repeat orbits during a period of 4 years are used to compute the wave number spectra of mesoscale variability for ascendant and descendant satellite tracks. The instrument noise level (about 0.5-0.6 m/sup 2/) has limited the resulting oceanic spectrum to wavelengths longer than 200-300 km. The radius of correlation for the ascendant tracks is 200 km and differs from the one for descendant tracks, which is 300 km. The ascendant tracks are directed nearly along the main current and corresponding along-track wavenumber spectrum is similar to spectra typical for high-energy ocean areas. It has a broad spectral 'bump' for wave lengths 500-1000 km. The descendant tracks are directed across the current, the spectrum is smooth and similar to spectra in low-energy ocean areas. This difference demonstrates the strongly anisotropic character of mesoscale variability in the region of the Gulf Stream, where the frontal zone plays the role of a specific waveguide for high-energetic trapped quasi-geostrophic waves, propagating along the front. >