Temporally Varying Mesoscale Eddy Characteristics in the California Current System Identified from RAFOS Floats

Abstract

The SOund Fixing And Ranging (RAFOS) floats were deployed by the Naval Postgraduate School (NPS) near California coast from 1992 to 2004 at depth between 150 and 600 m (http://www.oc.nps.edu/npsRAFOS/). Each drifter trajectory is adaptively decomposed using the empirical mode decomposition (EMD) into low-frequency (non-diffusive, i.e., current) and high-frequency (diffusive, i.e., eddies) components. The identified eddies are mostly anticyclonic with total 203 anticyclonic and 36 cyclonic spirals. Eddy characteristics are determined from the time series of individual RAFOS float trajectory. They are the current velocity scale, eddy radial scale, eddy velocity scale, eddy Rossby number, and eddy-current kinetic energy ratio. The California Current System is found an eddy-rich system with the overall eddy-current kinetic energy ratio of 1.78. It contains submesoscale and mesoscale eddies. The horizontal length scale of 10 km is a good threshold of the eddy radial scale (Leddy) to separate the two kinds of eddies. The mean eddy Rossby number is 0.72 for the submesoscale eddies and 0.06 for the mesoscale eddies. The current-eddy kinetic energy ratio is similar between submesoscale and mesoscale eddies. This may imply similar current-eddy kinetic energy transfer for submesoscale and mesoscale eddies. Statistical characteristics and interannual variability of current velocity scale and eddy characteristic parameters are also presented.

Descriptors:
Empirical mode decomposition; Eddy radial scale; Eddy velocity scale; Eddy rossby number; Eddy-current kinetic energy ratio.