Ph.D. Program in Oceanography and Global Change at the Canary Islands, Spain
Anatomy of a subtropical mode water eddy
An interdisciplinary survey of a subtropical mode water eddy was conducted within the Canary Eddy Corridor in September 2014. The anatomy of the eddy is investigated with near submesoscale fine resolution 2D data and coarser resolution 3D data. The eddy was 4 months old, at least 500 m deep and 40 km in radius. It may be viewed as propagating negative anomaly of potential vorticity (PV). We observe two cores of low PV: one in the subsurface layers centered at 90 m and another broader core located between 175 m and the maximum sampled depth of the 3D data (325 m). The subsurface core is where the maximum values of normalized relative vorticity, Ro=0.6, and azimuthal velocity, U=0.5 m s-1, are reached, and is defined as the eddy dynamical core. The dynamical core, 30 km in radius, is in solid body rotation with period of 4 days. Content of kinetic energy (KE) exceeds available potential energy (APE), KE/APE=1.58. Inferred available heat and salt content anomalies are 2.9 × 1018 J and 14.3 × 1010 kg, respectively. Vertical velocity (w) is estimated from 3D density and horizontal velocity fields through a generalized omega equation. Although complex, the inferred w field shows a basically dipolar structure. At the eddy center w is zero and maximum absolute values are located at the eddy periphery (6 m day-1). Coinciding with the occurrence of the w cells a noticeable enhancement of phytoplankton biomass is observed at the eddy periphery.