Eulerian and Lagrangian Statistics from Surface Drifters and a High-Resolution POP Simulation in the North Atlantic

Abstract

Eulerian and Lagrangian statistics were calculated from the North Atlantic surface drifter dataset for the years 1993–97 and a high-resolution eddy-resolving configuration of the Los Alamos National Laboratory (LANL) Parallel Ocean Program (POP) model. The main purpose of the study was to statistically quantify the state of the surface circulation in the North Atlantic Ocean for this period and compare it with the equivalent modeled state. Diffusivities and time and length scales are anisotropic over most of the ocean basin, except in most of the subpolar regions. Typical time and length scales are 2–4 days and 20–50 km. Longest timescales are found in the energetically quiescent regions in the south and southeast sectors of the basin. The longest length scales are found in the energetic western boundary current system, the most dispersive region of the domain. In many respects the eddy-resolving model reproduced a surface circulation in good statistical agreement with that depicted by the drifters. Model time and length scales were also anisotropic, with typical timescales of 2–4 days and length scales of 20–50 km in the zonal direction, and 30–50 km in the meridional direction. An eddy-permitting POP simulation produced unrealistic time and length scales that were too long and too short relative to the drifter scales; these were attributed to the model being too stable hydrodynamically.