Turbulent behavior of a fine mesh (1/12°) numerical simulation of the North Atlantic

Abstract

The geostrophic turbulent behavior of a fine mesh (1/12°) numerical simulation of the North Atlantic is discussed and compared to observations and coarser numerical simulations. The Miami Isopycnic Coordinate Ocean Model (MICOM) was configured for the North and Equatorial Atlantic (28°S–65°N) with a horizontal resolution of 1/12° (average mesh size on the order of 6 km) and 16 layers in the vertical. Such a set-up demands the latest in high performance computing. The unique aspects of this simulation are (a) a correct Gulf Stream separation from the North American coast and (b) high eddy activity. These results support the view that an inertial boundary layer (which results from the fine resolution) is an important factor in the separation process and that resolution of the first Rossby radius of deformation is necessary for a correct representation of baroclinic instabilities. Sea surface height variability spectra are computed from the model results and compared to observations and previous models, within the framework of the geostrophic turbulence theory. Length scales representative of the simulated eddy field compare well with observations based on altimeter data. Despite higher eddy activity, there is no significant geographic variation in spectral slope in the inertial ranges consistent with previous simulations with coarser resolution. Observations, on the other hand, show a flattening in the spectra derived from altimeter data in weakly energetic areas when compared to spectra from highly energetic areas of the Atlantic. The possible impact of mechanisms not represented in the model, such as high frequency and high wave number wind forcing, is then discussed.