PRELIMINARY-RESULTS ABOUT THE STABILITY OF AN INTERMEDIATE WATER CURRENT

Experiments were run on a 14 m diameter rotating platform to study the stability conditions for a constant Volume Row rate current of interm ediate water. The Row was introduced in a two-layer system initially a t rest in solid body rotation, along the sidewall of the tank, and all owed freely to evolve. A sink collected the intermediate water and thu s ensured that the free surface height was constant. Thus the upstream conditions were the rotation rate, the volume dow rate, the density a nd the initial width of the intermediate current, which was in geostro phic equilibrium when it left the source; i.e. its thickness along the wall at the source was fixed by this condition. The relevant paramete rs appear to be the Ekman and the Burger numbers. The data collected f rom the experiments are very consistent, and it appears that there wer e five typical Row regimes: (1) a stable current along the whole basin (2) a series of cyclonic vortices attached to the outer edge of the c urrent, with an upstream stable current; (3) a large cyclonic vortex a ttached to an anticyclonic instability; (4) dipoles shed from the curr ent into the interior fluid; and (5) generation of lenses of intermedi ate water, similar to meddles. This last result shows that no topograp hical effect is required to generate such long-lived lenses, which the n drift slowly upstream as the dipoles do.