Eulerian and Lagrangian Velocity Distributions in the North Atlantic

Abstract

Velocity probability density functions (PDFs) are calculated using data from subsurface current meters in the western North Atlantic Ocean. The PDFs are weakly, but significantly, non-Gaussian. They deviate from normality because of an excess of energetic events, and there are evidently more such events in the main thermocline than in the deep ocean. The PDFs are also compared with those obtained from subsurface floats in the same region. The PDFs are statistically indistinguishable so long as the float data are averaged in appropriately sized bins. Taking too-small bins yields overly Gaussian float PDFs, and taking too-large bins yields too-non-Gaussian PDFs. With this caveat, the Lagrangian and Eulerian PDFs agree, consistent with expectations from theory and previous numerical simulations.