Interactions between Near-Inertial Mixed Layer Currents and the Mesoscale: The Importance of Spatial Variabilities in the Vorticity Field

Abstract

Satellite-tracked mixed-layer drifter data from the 1987 Ocean Storms Experiment in the northeast Pacific are used to study the temporal and spatial variability in the near-inertial currents of the surface mixed layer. The data suggest that the near-inertial currents interact with the mesoscale vorticity. To explore the exact nature of this relationship, an asymptotic analysis is extended to include the mesoscale and it is shown that not only gradients in the planetary vorticity (?) but also the gradients in the mesoscale vorticity affect the generation and evolution of near-inertial mixed layer currents. While the ? effect is relevant for the large-scale evolution of the near-inertial currents, the vorticity gradients of the mesoscale field determine the local behavior of near-inertial currents. Using a three-dimensional model it is shown that areas of large gradients in the mesoscale vorticity coincide with areas of low near-inertial energy. The smaller spatial scales in the near-inertial energy, generated by the vorticity field, result in faster decay of near-inertial currents. The findings that the near-inertial currents interact with the mesoscale are in apparent contradiction with previous research in the same area.