Satellite-Tracked Drifter Measurements of Inertial Currents in the Gulf of Mexico

Over 2200 satellite-tracked drifters have been air deployed from fixed wing aircraft into the Gulf of Mexico over the past 25 years as part of a Loop Current monitoring program. The drifters are cylinder shaped and are approximately 96 cm tall and 12 cm in diameter. They each have a 45 m tether attached to a 1.2 m diameter drogue/chute. While the drifter design allows for cost-effective monitoring of mesoscale variability, the drogue/buoy pairing is not ideal for measuring wind-driven currents since the effective drogue depth is strongly dependent on shear near the surface and at the base of the mixed layer. However, in 2002 the buoys were upgraded with GPS receivers which provided more accurate positions than standard Argos tracking. With the improved measurements, inertial current and wind-driven variability is now clearly evident in the drifter trajectories. An analysis of the data shows that near-inertial variability is strongest during June. The data also reveal that the variability is reduced over the Loop Current. This is consistent with previous studies showing low near-inertial energy near regions with large gradients in mesoscale vorticity.