An Inverse Calculation of Glider-based Absolute Geostrophic Currents in the Gulf of Mexico

The ability to retrieve ocean currents from various observational platforms is important for studying ocean circulation and its variability. Autonomous buoyancy-driven gliders allow for the generation of upper ocean density profiles using in-situ, high-resolution temperature and salinity measurements to depths of about 1000 meters. Based on the calculated density field, geostrophic currents can be estimated using the thermal wind equation. The thermal wind equation relates the horizontal density gradients to the vertical shear of the horizonal geostrophic currents. The horizontal gradients of the density field along the glider track are vertically integrated to estimate geostrophic velocities perpendicular to the glider transect and relative to unknown velocities at a selected reference depth. In this project, we apply an inverse method to compute these unknown reference velocities and thus determine the absolute geostrophic velocities at any depth along the glider transect. Absolute geostrophic velocities in this project are calculated from glider data obtained in the Gulf of Mexico in 2015 by members of the Gulf of Mexico Coastal Ocean Observing System. This approach for computing absolute geostrophic velocities is particularly useful for the most common glider configurations, which do not feature direct current measurements from mounted acoustic Doppler current profilers.