One of the most important mechanisms in the redistribution of energy in the ocean is energy propagation through Rossby waves. The Rossby wave mechanism removes energy from the ocean interior into the western boundary currents. It plays a key role in the energy balance of the steady state, large scale ocean circulation. (The steady state is studied in Exercise 6.)

Rossby wave movement can also be seen in aspects of ocean current variability, such as eddies and meanders. The term "Rossby wave" is a reminder that the propagation speed with which such features move westward is derived from a wave equation; but Rossby wave propagation is not restricted to wave-shaped disturbances of the mean circulation.This exercise demonstrates how irregularities in the shape of the permanent thermocline, produced for example by large eddies, move westward with Rossby wave speed, eventually feeding into the powerful western boundary currents.

In the temperate, subtropical and tropical regions the dynamics of the deep ocean are well described by a model which approximates the oceanic stratification by two layers of different density. The interface between the layers (the model equivalent of the permanent thermocline) is located at a few hundred metres depth. The basic assumption of the model is that all water movement occurs in the upper layer, while the lower layer is at rest; this is known as a 1¹/₂ layer model.

The exercise begins with a model of the 1¹/₂ layer ocean, in which the layer interface is represented by the 15ºC isotherm, continues with an example of eddies from the East Australian Current and concludes with some examples of observations from the open ocean.

The model data are based on Gulf Stream eddies from the Sargasso Sea and represent either a cyclonic or an anti-cyclonic eddy. The density difference Δρ between the upper and lower layer is set to 3 kg m^-3 (uper layer density: 1024 kg m^-3, lower layer density: 1027 kg m^-3).

Select the type of eddy you wish to study:

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