Comparison of Geostrophic Current Estimates from a Bouyancy Glider and a Surface Current Analysis from Satellites in the Gulf of Mexico

Abstract

Our ability to estimate surface geostrophic currents in the ocean has improved over the recent decades by the availability of observations from satellite altimeters and autonomous buoyancy-driven underwater gliders. In this study, a comparison between geostrophic velocities estimated from a glider mission in the Gulf of Mexico and a surface current analysis derived from satellites is done. The goal is to evaluate the effectiveness of using the glider measurements to estimate ocean current velocities. Glider data allows density profiles of the water column to be computed from temperature, salinity, and pressure measurements down to a depth of 1000 meters. These density profiles allow computing the along-track density gradients, which in turn are used to estimate the vertical shear of the geostrophic velocities perpendicular to the glider transect. The vertical shear is then integrated vertically to estimate vertical profiles of geostrophic velocity relative to 500 meters where the reference velocity was assumed to be zero. The comparison shows that the surface currents estimated from the glider and those from the analysis agree well. Differences between the two velocity fields are attributed to the different dynamical assumptions involved, glider quality control, and spatial and temporal sampling errors. The analysis also underscores the need to combine the glider-relative current observations with observations of the reference velocities.