Eddy properties in the Southern California Current System

TitleEddy properties in the Southern California Current System
Publication TypeJournal Article
Year of Publication2018
AuthorsChenillat F, Franks PJS, Capet X, Riviere P, Grima N., Blanke B, Combes V
JournalOcean Dynamics
Date Published2018/07
Type of ArticleArticle
ISBN Number1616-7341
Accession NumberWOS:000435673500001
Keywordsboundary upwelling systems; California upwelling system; dynamics; Eddy dynamics; Lagrangian; Lyapunov exponents; Mesoscale eddies; Numerical study; ocean eddies; oceanography; Pacific sardine; part i; study; submesoscale transition; surface; variability

The California Current System (CCS) is an eastern boundary upwelling system characterized by strong eddies that are often generated at the coast. These eddies contribute to intense, long-distance cross-shelf transport of upwelled water with enhanced biological activity. However, the mechanisms of formation of such coastal eddies, and more importantly their capacity to trap and transport tracers, are poorly understood. Their unpredictability and strong dynamics leave us with an incomplete picture of the physical and biological processes at work, their effects on coastal export, lateral water exchange among eddies and their surrounding waters, and how long and how far these eddies remain coherent structures. Focusing our analysis on the southern part of the CCS, we find a predominance of cyclonic eddies, with a 25-km radius and a SSH amplitude of 6 cm. They are formed near shore and travel slightly northwest offshore for similar to 190 days at similar to 2 km day(-1). We then study one particular, representative cyclonic eddy using a combined Lagrangian and Eulerian numerical approach to characterize its kinematics. Formed near shore, this eddy trapped a core made up of similar to 67% California Current waters and similar to 33% California Undercurrent waters. This core was surrounded by other waters while the eddy detached from the coast, leaving the oldest waters at the eddy's core and the younger waters toward the edge. The eddy traveled several months as a coherent structure, with only limited lateral exchange within the eddy.

Short TitleOcean Dyn.

This study has focused on mesoscale activity in the Southern CCS using a 5-km horizontal resolution model. Using an eddy detection and tracking algorithm based on the Okubo-Weiss parameter, we found that mesoscale activity in the SCCS was dominated by cyclonic eddies, consistent with in situ data (Stegmann and Schwing 2007). On average, these eddies have a diameter of 50 km and can remain distinct for up to 190 days. The vertical structure of the average cyclonic eddy obtained from averaging ~ 4000 eddies shows a consistent doming of isopycnals in the eddy center, bringing deep, cold, salty, and nutrient-rich water closer to the surface. These cyclonic eddies are formed at the coast through current instabilities, mostly in the fall. Eddies consistently trapped water from the northward-flowing California Undercurrent and the southward-flowing shallow California Current, and transported these water masses offshore at a speed of ~ 2 km day−1.

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