Laboratory simulation of the gyre in the Alboran Sea

Abstract

A laboratory experiment is described which appears to exhibit flows which are similar to the flow‐counterflow in the Strait of Gibraltar and, for certain values of the parameters involved, to the gyre and front in the western Alboran Sea. The experiment is transient in nature and is made with two connecting basins on a rotating turntable. A sliding door is fitted into the channel connecting the two basins. Each basin is filled with water, the door is closed, and salt is added to one side so that the two waters have different densities. After the waters have spun up to rest in the rotating frame, the door is opened. A flow, driven by the density imbalance, is observed shortly thereafter, the lighter fluid rising up over the heavier fluid and pushing into the basin containing the heavy fluid. Likewise the heavy fluid pushes into the basin containing lighter fluid. For very rapid rotation these flows are violently unstable. For less rapid counterclockwise rotation both currents stay confined to a narrow jet which clings to the right‐hand wall of the basins which they are entering. At some lower rate of rotation the jet cannot hold to a sufficiently curved wall, and the jet separates from the wall—a gyre is observed between the jet and the wall. The gyre and the jet initially are both a Rossby radius in size, but gradually the gyre grows larger. Growth of the gyre seems to result from an accumulation of fluid from the jet as it returns to the wall. Scaling arguments and estimates of buoyancy, Coriolis, and wind forces are advanced in support of the concept that this laboratory‐produced gyre and the gyre in the Alboran Sea share the same dynamics.