Effects of Horizontal Resolution in Numerical Models on Evolution of Denmark Strait Overflow and Energy Transfers

The Denmark Strait Overflow (DSO) represents the most important transport branch for dense and cold water formed north of the Greenland-Scotland ridge to the North Atlantic. Previous studies using long climate model simulations have shown that the DSO has a substantial impact on the variations of AMOC (Lohmann, 2014). However, the overflow is found in an eddy rich region so that it is difficult to represent with a coarse resolution that is typical of climate models.

In this study effects of horizontal model resolutions on the DSO simulations are investigated in terms of ocean energetics and evolution of overflow properties. For this purpose, 5 different simulations with horizontal resolutions ranging from 1km to 18km carried out using the MIT General Circulation Model for a 1 year period with a regional setup.

As the resolution decreases the overflow becomes less and less energetic as expected. The most energetic part of the overflow is found between 100km to 300km downstream of the sill. Energy transfer from mean kinetic energy to eddy kinetic energy shows a peak between 100-200km whereas transfer from eddy available potential energy to eddy kinetic energy is stronger between 200km to 300km downstream. In coarser simulations, the mean potential energy decreases much faster, consistent with high numerical mixing. In the 18km resolution, eddy available potential energy is negligible along the whole flow path, and lack of eddy activity results in further deterioration of the overflow structure downstream.