Estimating the Surface Transport of Meandering Oceanic Jet Streams from Satellite Altimetry: Surface Transport Estimates for the Gulf Stream and Kuroshio Extension

Abstract

A method has been developed to detect the location, width maximum velocity, and suffice transport of a meandering oceanic jet stream from satellite altimetry. Ale method is based on a nonlinear least squares scheme, in which Gaussian-shaped velocity profiles are fitted to explain the observed current variability in the meandering region. The method has been applied to 25 Geosat tracks in the Kuroshio Extension and Gulf Stream for the first you of the Geosat Exact Repeat Mission. A reasonably smooth circulation pattern has emerged for the surface transport for both currents (at opposed to the widely varying direct transport estimates). After leaving the coast, both currents have surface strength of the order of 90 ? 103 m2 a?1(equivalent to a 90 cm height jump, i.e., the sea surface height difference across the jet). They continue to gain strength downstream until a maximum of the order of 130 ? 10 3 m2> a?1 is reached (near 150°E for the Kuroshio and 63°W for the Gulf Stream). The Gulf Stream then decays in strength slowly. At 55°W, the surface transport is estimated to be 128 ? 103 m2 s?, which compares well with Richardson's estimate of 122 ? 103 m2 a?1 derived from surface drifter observations. The Kuroshio Extension decays at a much faster pace. The surface transport has delayed to 68 ? 103 m2 s?1 near 165°E, which em be referenced to Joyce and Schmitz's estimate of 57 Sv (Sv ≡ 106 m3 s?1) in total transport. The mean position of the jet for the one-year record tends to lie close to where the sea level variability is maximum along each track. And it compares wed with the long-term average derived from IR imagery for the Gulf Stream. However, the standard deviation for the one-year record 2VM less wed with IR imagery west of 64°W in the Gulf stream possibly because the record is not long enough. Preliminary examination of the one-year-long record seems to suggest the existence of a seasonal cycle in the intensity of both the surface transport and the eddy field around the Kuroshio Extension, which is the weakest in the winter and gets progressively stronger towards the fall. A similar seasonal cycle seems to exist for the Gulf Stream surface transport averaged between 64° and 73°W.