Challenges in Capturing Wind-Driven Motions in Satellite-Derived OSCAR Surface Currents

Ocean Surface Current Analyses-Realtime currents (OSCAR, podaac.jpl.nasa.gov) are global ocean surface mixed layer velocities calculated from satellite-sensed sea surface height gradients, ocean vector winds, and sea surface temperature fields using geostrophy, Ekman, and thermal wind dynamics. OSCAR’s continuing improvement depends on better modeling of the momentum transfer both within and across the boundaries of the turbulent mixed layer. A main research objective of the OSCAR project is to improve the generation of surface currents by ocean vector winds, and in doing so further our understanding of the mechanisms behind the transfer of momentum between the atmosphere and the ocean through the planetary boundary layer.

OSCAR has historically used quasi-steady Ekman dynamics for its wind-driven component. This is insufficient for capturing the wind-driven component of surface currents on fast time scales or small space scales. Time dependence, vertical variation, high-resolution wind fields, different turbulence parameterizations, and surface wave effects are all presently being investigated for incorporation into the OSCAR model. The calculated surface currents are evaluated for success against currents observed by global drifting buoys.

The purpose of this presentation is to characterize under what dynamical conditions and in what regions the biggest matches and mismatches between OSCAR and drifters occur. We will characterize the variability and success of results across different models and as they vary with physical features such as high versus low winds, persistence of wind direction, inertial wave activity, and proximity to coasts. The intention is to understand better which physical processes dominate the generation of mixed layer currents under a variety of conditions.