A model-dye comparison experiment in the tidal mixing front zone on the southern flank of Georges Bank

Abstract

A process-oriented model-dye comparison experiment was conducted to examine the ability of a numerical ocean model to simulate the observed movement of dye across the tidal mixing front on the southern flank of Georges Bank during 22–26 May 1999. The experiment was made using the unstructured-grid Finite-Volume Coastal Ocean Model (FVCOM) with varying horizontal resolution. The results indicate that the observed cross-isobath movement of the dye patch was primarily controlled by meso-scale temporal and spatial variability of the water temperature and salinity fields. Onset of vertical stratification tended to slow down an upward stretching of the dye column and trapped the dye within the bottom mixed layer. To reach a convergent numerical solution that reproduced the observed lateral turbulent dispersion of dye, the FVCOM grid required a horizontal resolution of ∼500 m in the dye study region. Within the tidal mixing front of Georges Bank, the movement of the center of the dye patch was mainly driven by the ensemble velocity integrated over the dye volume, with a first-order contribution from vertical shear of the dye's horizontal velocity.