Analysis of Legeckis eddies in the near-equatorial Pacific

A study of Legeckis eddies in the equatorial Pacific during seasonal period s of high zonal shear between the Southern Equatorial Current and the North ern Equatorial Counter Current is undertaken. We use both Geosat and TOPEX altimetry data, in combination with advanced very high resolution radiomete r (AVHRR) temperature fields and numerical results generated by the Paralle l Ocean Climate Model (POCM). Geosat data analyzed using the Marquardt-Leve nberg Fourier series algorithm [Dayyani et al., 1996], exhibit eddy feature s in good qualitative agreement with both Linear stability theory of the zo nal barotropic flow and with other independent field and satellite observat ions. A comparison of sea surface height (SSH) and sea surface temperature (SST) anomaly fields suggests that the phase relation between them may be e xplained in a first approximation by simple cat's-eye kinematics [Musman, 1 989]. This is explored further using the POCM, TOPEX, and AVHRR data. The P OCM time series of SST and SSH anomalies obtained during a time of quasi-st eady eddy propagation clearly show that the phase phi between their respect ive minima varies continuously with latitude, ranging from near zero at lat itudes well below the separatrix of the cat's eye to values approaching pi radians at latitudes near the critical layer of the cat's eye. The unsteady wave systems observed in both the Geosat and TOPEX SSH anomaly data show t he birth and death of individual eddies, with a fairly clear trend that bir ths occur 1 degrees N of the zonal wave train while deaths occur only in th e latitude of the mature wave train.