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Abstract. Sea surface height anomaly data from satellite are continuously available for the entire Gulf of Mexico. Surface current velocities derived from these remotely sensed data are compared with surface velocities from drifting buoys. The comparison shows that satellite altimetry does an excellent job resolving gulf eddies over the shelf rise (depths between ---200 and 2000 m) if the proper length scale is used. Correlations between altimeter-and drifter-derived velocities are statistically significant (r > 0.5) when the surface slope is computed over 125 km, indicating that remotely sensed sea surface height anomaly data can be used to aid the understanding of circulation over the shelf rise. Velocity variance over the shelf rise from the altimetry data shows regions of pronounced eddy energy south of the Mississippi outflow, south of the Texas-Louisiana shelf, and in the northwest and northeast corners of the gulf. These are the same locations where surface drifters are most likely to cross the shelf rise, suggesting gulf eddies promote cross-shore flows. This is clearly exemplified with both warm and cold eddies. Finally, the contribution of gulf eddies and wind stress to changes in the mean circulation are compared. Results indicate that the eddy-generated vorticity flux to the mean flow is greater than the contribution from the surface wind stress curl, especially in the region of the Loop current and along the shelf rise base in the western gulf. Future modeling efforts must not neglect the role of eddies in driving gulf circulation over the shelf rise.

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Geosat Exact Repeat Mission (ERM) altimetric measurements of the sea surface height in t.heGulf of Mexico are used to determine the mean sea surface height with respect to the ellipsoid and mesoscale variability along Geosat ground tracks in the gulf for the time period from November 8, 1986, to November 25, 1988. The alongtrack mean sea surface is dete•m:tined using a regional crossover adjustment procedure, in which the tilt and bias of mean arcs are estimated using a least squares technique to minimize the height differences at crossovers points. A mean sin'face generated using the Geosat ERM alongtrack mean is calculated and corttrasted with a previously derived mean surface determined using GEOS 3 and Seasat crossover differences. This provides a first look at the variability in the mean between the time periods of 1987-1988 and 1975-1978. In addition, the alongtrack mesoscale varigbility time series has been produced h'om the Gcosa• ERM data set by using a robust orbit error removal algorithm to detex•ninc the variability of t lm sea surface height with respect to the alongtrack mean. A sin'face generated using thc rms ooe this alongtrack time series shows good qualitative and quantitative aga-eemex•t wit. h previous in situ observations in the region. This study demonstrates the potential of satellite al[imct. ry 1'o,' oceanographic studies of the Gulf of Mexico. !. INTRODUCTION[1988] from satellite IR image analysis. From these studies one would expect that during the time period under consid-Previous studies have proven the viability of using colin-eration here, at least two samples of major eddy shedding ear altimetric measurements to remotely observe the Loop cycles would be observed. In fact, the variability time series Current intrusion and anticyclonic eddy shedding in the Gulf produced for this study shows evidence of two shed eddies of Mexico [Thompson et al., 1983; Thompson, 1986]. This is propagating westward for the entire length of the deep an important result since the thermal signature of the Loop ter basin of the gulf after shedding from the Loop Current. Current and its associated eddies is undetectable in infrared In addition, the last half of an eddy cycle in the western s•tellite imagery from June through October because of a gulf appears at the beginning of the time series. Thus we shallow surface layer of warm water covering the gull With have a sampling period for computation of a mean and the the maneuvering of the Navy satellite Geosat into an ex-variability about that mean in the Gulf of Mexico which is act repeat orbit, an unprecedented wealth of oceanographic sufficiently long to begin analysis. As additional data bedata with a high degree of temporal and spatial resolution come available we will expand the time series and revise our is now available for the study of gulf dynamics. The results preliminary estimates. presented here are an initial examination of the first 2 years The only previously published altimetric mean sea surof this data set. faces with estimates in the G...