Eddy activity in the four major upwrelling systems from satellite altimetry (1992-2007)

Eddy activity in the four major eastern boundary upwelling systems (EBUS) is investigated using 15 years of satellite altimetry data. Based on the analysis of more than 4000 long-lived eddy trajectories in every EBUS, we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator. These mesoscale eddies, having radii of 70-160 km, are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies. Temporal variations of the number of newly-formed eddies and the associated eddy activity index, defined as the mean eddy energy density, are finally examined at seasonal and interannual scales. The strongest seasonal (interannual, respectively) variations are observed in the California (Benguela) upwelling systems. The proposed indices also exhibit contrasted long-term trends in each EBUS, which suggests that eddy activity might be sensitive to a warming climate. (C) 2009 Elsevier Ltd. All rights reserved.