Meddy coupling with a deep cyclone in the Gulf of Cadiz.

Hydrological measurements made in July 1999 in the Gulf of Cadiz reveal the presence of two meddies, one south of Cape Saint Vincent (meddy Christine, centered at 9°45′W–35°30′N), the other one near the Moroccan shelf (meddy Isabelle, centered at 8°30′W–34°25′N), and their interaction with a deep cyclone (centered at 8°30′W–35°15′N). These meddies are medium-scale features with thermohaline anomalies of 60–70 km diameter concentrated between 750 and 1500 m depths; these anomalies reach 2 °C and 0.5 in salinity. Meddy Christine exhibits unusually strong thermohaline gradients at its periphery. Their maximum azimuthal velocities are 0.12 m/s (meddy Isabelle) and 0.10 m/s (meddy Christine). They both have a (vertically) tripolar structure in potential vorticity anomaly. The cyclone is shallower (between 600 and 1300 m) with a weaker signature of Mediterranean water (12 °C at 800 m, 36.2 in salinity between 800 and 1200 m). Its velocity maximum (0.16 m/s) is also centered near 800 m. This cyclone appears coupled with meddy Isabelle as a baroclinic dipole. This dipole tears a long warm and salty filament away from meddy Christine at 1200 m. The long-term evolution of these eddies is described by means of deep-drogued drifting buoy trajectories: while meddy Christine drifts southwestward, the two other eddies remain close to each other and move together along the continental shelf towards Cape Saint Vincent where they separate. A three-layer quasi-geostrophic model is used to evaluate the possible origin of meddy Isabelle and of the cyclone near the Portuguese coast, and to assess if their interactions, both mutual, with the domain boundaries, and with bottom topography, can account for their motion. The interaction of this dipole with meddy Christine is also quantified in this model.