Looping RAFOS floats in the California Current System

Abstract

Looping motions of RAFOS floats deployed off the Central California coast between 1992 and 2010 are described. Most floats were deployed in the California Undercurrent. Floats at 300 m were observed to loop 26% of the time, with anticyclonic rotation observed about twice as often as cyclonicrotation. Characteristics of anticyclonic rotation at 300 m included median swirl speeds of 14 cm/s for diameters of 59 km and 14-day periods. Long-lived (>70 days and at least 8 consecutive loops) anticyclonic loopers are identified as California Undercurrent eddies (or ‘‘cuddies’’). One cuddy was observed to move southwestward 1650 km over a period of 520 days before observations ended. Kinematically, cuddies are similar to Mediterranean Water eddies (meddies) in the Iberian Basin, except that meddies are somewhat stronger, larger and deeper. Over the slope,most cuddies were formed between either Pt. Sur and Pt. Reyes or Cape Mendocino and Cape Blanco. The region north of Cape Mendocino is estimated to generate six cuddies each year. These eddies form from waters on the inshore side of the California Undercurrent as they move past Cape Mendocino. Topographic drag is the most likely formation mechanism. Two of eight deep floats were observed to loop, one anticyclonically (1545 m) for 279 days and the other cyclonically (1167 m) for 192 days. Looping for these floats ended near Taney Seamounts.