Kinematics and dynamics of a cyclonic eddy off Pt. Arena, California

Abstract

In situ hydrographic data and remotely sensed sea surface temperature data were analyzed to describe the kinematics and dynamics of a cyclonic eddy observed off Point Arena, California, in May 1993. The hydrographic data were first objectively analyzed using multiquadric-biharmonic interpolation (M%B) to obtain a three- dimensional field of density. This was then used in a primitive equation (PE) model with a digital filter initialization method to arrive at the dynamically balanced three-dimensional velocity field, including the vertical motion. Several aspects related to geostrophic adjustment, to data analysis and to the lack of exact synopticity in the observations were examined; these include the effects of internal tides, eddy rotation and MQ-B parameters sensitivity analysis. The results reveal a cyclonic circulation with meanders in the otherwise nearly circular flow, and maximum horizontal speeds of about 40-5O cm/s at the surface. The meanders have associated patterns of radially aligned patches of sinking and rising motion, extending coherently to about 500 m depth, with maximum vertical velocities of 2022 m/day between 100 and 150 m depth. Because of the strong horizontal currents and the short horizontal length scales involved, the particle vertical excursions are very small.