Modelling Mesoscale Features in the Ocean

Abstract

The dominant dynamic length scale in the ocean, as well as in the atmosphere, is the Rossby radius of deformation (e.g., Gill, 1982 pp. 191 – 203). In the atmosphere this length scale is the scale of the low pressure systems, i.e. about 100 –1000 km, which is referred to as the synoptic scale. In the ocean the Rossby radius of deformation varies from about 100 – 300 km in tropical waters down to 5–10 km in subpolar regions like the Norwegian Sea. Length scales such as the latter are commonly referred to as the mesoscale by meteorologists. This reference has also been adopted in the ocean, although from a dynamical point of view, it would have been natural to name it the oceanic synoptic scale. The name mesoscale is, therefore, traditionally associated with a particular range in kilometers rather than being associated with its similar dynamic atmospheric length scale. Oceanic features of the order of the Rossby deformation radius, which may be dubbed oceanic ‘weather’, are nevertheless referred to as mesoscale features. Examples of such features are upwelling jets, eddies and filaments. These features are clearly visible in almost any satellite image of the ocean surface.