A census of Meddies in a long-term high-resolution simulation

Abstract

The output from a high-resolution two-decade long Mediterranean Outflow simulation is analysed here to provide a census of Mediterranean Water eddies (aka Meddies), both anticyclones and cyclones. The formation rate of Meddies that survive for at least 90days is of 12 Meddies yr−1 of which ∼12% are cyclones. The rate of formation reaches 40 Meddies yr−1 (30% cyclones) when considering all the Meddies living over 15days. About 70% of the population is born along the southwestern Iberian slope, but several robust Meddies also originate in points of convergence of the main pathways into the open ocean. The longest-lived Meddies propagate northwestwards, but most of the anticyclones veer southwestwards after a while. As the Meddies drift away from their birthplace, their radius tends to increase gradually from 15 to 30km. The thickness (depth-difference between isopycnals 27.2 and 27.5) of anticyclones born near Cape St. Vincent contracts by approximately 100m, after travelling 1000km from their source; their mean swirl velocities range from about 21cms−1 (at z=1000m) up to 27cms−1 (at z=600m). Mean salinity and temperature anomalies are significantly lower for cyclones, which in general are also more slowly rotating, shallower and thinner than anticyclones. Cyclones are more easily tracked at 600m depth where longer trajectories are recorded. In the vicinity of Portimão Canyon, cyclones outnumber anticyclones while the reverse happens downstream of Cape St. Vincent.