Observed Interaction between Low and High Frequency Motions off the Coasts of Peru and California

Abstract

Datasets taken near the coasts of Peru and California have been analyzed to explore the evidence of a correlation between the high frequency (period < 10.8 hour) and low frequency (period > 4 day) motions. A large part of the high frequency current is consistent with internal wave dynamics. They have a near 180° phase change across the water column; there is also evidence of a clockwise veering with depth, presumably due to frictional effects. No correlation of the vertical Reynolds stress vw and vertical shear Vz is found. The horizontal stress uv is found to be negatively correlated with the horizontal shear Vx only when averaged over time and space scales larger than those of the mean velocity field. The implied eddy viscosity is of order ?H ?105 cm2 5?1. It is suggested that the relaxation time for the wave field to lose asymmetry is larger than the time for the wave to propagate across a typical scale of the mean shear field. Due to this the fluctuating field may locally behave like a negative eddy viscosity at certain places.