HIGH-FREQUENCY VARIABILITY OF WESTERN BOUNDARY CURRENTS USING ERS-1 3-DAY REPEAT ALTIMETER DATA

ERS 1 three-day repeat altimeter Ocean products have been analyzed fro m September 3 to December 9, 1991. In the high mesoscale energy areas of the world ocean the obtained height variability is comparable to th at derived from 2 years of Geosat altimeter data (17-day repeat), whil e it is slightly lower elsewhere. The data reveal some high-frequency variability of western boundary currents, but not the seasonal Signals ,nor the low-frequency mesoscale signal which dominates elsewhere. Iso correlation maps show that the e-folding time is around 10 to 15 days in Strong currents. The sea height variance, integrated over all wavel engths in the frequency-wavenumber spectrum, corresponds to less than 5% of the total 3-month variance for periods shorter than 20 days, up to 15% of this variance for periods shorter than 34 days, which are re spectively the Nyquist frequencies of the TOPEX/POSEIDON and Geosat da ta. This signal covers a whole range of wavelengths that cannot be obt ained from current meter data. In the Gulf Stream area the total dynam ic height signal is estimated by adding a climatological dynamic topog raphy to the mesoscale variability. Near 60 degrees W, the height vari ations apparently correspond to meanders with periods of 30 to 40 days and latitudinal extension about 200 km. They are consistent with west ward propagation at about 10 cm/s, and their surface transport varies by about 50% on this timescale, which is in agreement with in situ obs ervations.