Sack Lunch Seminar (SLS)

The accuracy of ocean components of climate models is thought to increase with resolution, and we examine this associated change in utility on a range of model fields. A 30-year integration (1978 to 2007) of the NEMO model at 1o, 1/4o and 1/12o is used to investigate the impact of modelling choices associated with horizontal resolution. Changes in degrees of freedom associated with the increasing resolution allow alternative energy dissipation pathways and their impact is assessed.

A distinct strengthening of the anti-clockwise component of the overturning is found in the Southern Ocean, primarily owing to the baroclinic component. The mixed layer does not change significantly with resolution, with results comparable to observations. Minor changes with resolution are attributed to increased numbers of fronts with better resolution. In the interior, steric height variability, specifically its covariance between the surface (<2000m) and the deep (>2000m) does change owing to eddy effects not captured by the Gent-McWilliams parametrization. Topographic interactions are assessed in terms of vortex stretching in the bottom pressure torque term. Major changes are found in the baroclinic component in the Southern Ocean. Low resolution appears appropriate for fields such as the mixed layer depth, but higher resolution is increasingly required for large scale features through allowing eddy activity.