EXPERIMENTAL-STUDY OF THE ALBORAN SEA GYRES

In order to examine the response of the surface flow to the regime in the Gibraltar Strait, the Alboran Sea is modelled in a large rotating channel mounted on the 14 m ''Coriolis'' rotating platform. The channe l is divided into two basins connected by a strait. The currents are i nitialized and maintained constant in time by pumps. When flowing out of the strait, the Atlantic current forms an anticyclonic gyre in the Mediterranean basin. This gyre is related to the Western Alboran Sea G yre and can develop until its diameter is as large as the width of the basin. Depending on the parameters, the flow exhibits different confi gurations, which we are able to characterize with the use of tracers ( food dye, floats). A very consistent result is that the flow seems to be deterministic, i.e. for the same initial and upstream conditions of stratification, rotation and flow rate, it shows the same pattern and the gyre evolves in the same manner. A parametric study shows that th e characteristics of the gyre (shape, size, stability) are highly depe ndent on the ratio of the internal radius of deformation over the widt h of the strait, r/w, but not on the Rossby number, Ro, based on the f low rate of the currents. A meander, related to the Eastern Alboran Se a Gyre, can form downstream of the gyre. Its presence depends on r/w a nd also on Ro. A row of cyclonic vortices can develop along the fronta l limit of the Atlantic jet. The growth rate of the Gyre is determined by a flux budget analysis. The mechanism involved in this process was analysed by Whitehead (1985) and the experimental data supports his c onclusions. We conclude that, whereas the internal radius of deformati on plays a role in the structure and the stability of the Western Gyre , the flow rate of the Atlantic current influences the growth rate of the Gyre but does not change the flow drastically. Finally, a comparis on with the numerical simulation of Speich (1992) shows a fairly good agreement in spite of some minor differences.