EXPERIMENTS ON SPIN-UP AND SPIN-DOWN ON A BETA-PLANE

Here we study the spin-up and spin-down of a homogeneous fluid with a free surface on an experimental 'beta-plane' and describe the importan t features for both cases over a range of parameters. Quantitative val ues are found for the velocity fields using a new image processing tec hnique that analyses a video record of particle motion and stores the results digitally. Streamlines, pressure fields and vorticity values a re found by interpolation techniques and result in a complete descript ion of the flow characteristics. We discuss the relationship between t he results of these experiments and those observed in large-scale homo geneous models of ocean circulation, e.g. Moore (1963). This study ext ends the work of van Heijst et al. (1990) to the case of spin-up in a rectangular container but of non-uniform depth and we note the differe nces to and similarities with their observations. It is related, also, to more recent results of Maas et al. (1992), who considered spin-up on a beta-plane but in a tank of very different proportions to the one considered here.