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Algerian Eddies are eddies formed via the instability of the Algerian Current (AC). The generation and propagation of AEs is described by Puillat et al. : Basically, instead of flowing steadily alongslope, the Algerian Current meanders. Part of the Modified Atlantic Water (MAW) then recirculates inside the meander, so that a surface anticyclonic eddy is created, embedded between the crest of the meander and the continental slope. Transient (on the order of several days) surface cyclonic circulations (CC) are also frequently observed on satellite images upstream from the meander crest, and have been evidenced in situ by drifting buoys trajectories and hydrology. However, only anticyclonic eddies can develop [,i.e. Algerian Eddies (AE)]. The generation of AEs is observed from approximately 0 to 8 degrees E. AEs trajectories begin with an alongslope-downstream propagation at few kilometers per day, while within their embedding meander, the water typically flows at roughly 50 kilometres/day. AEs diameters vary during their course between 50 and 150 km up to around 250 km. AEs lifetimes range from few weeks to several months. The maxima reported up to now are at least six months, with in situ observations, and at least nine months, with satellite images. AE maximum lifetimes are thought to be able to exceed three years.
The AEs alongslope-downstream propagation usually ends in the Channel of Sardinia, where AEs dramatically interact with the bathymetry. Most of them collapse and release MAW that continues to flow through the channel. A few AEs per year follow the deep isobaths northward across the channel and detach from the Algerian slope, which implies a deep structure. It is now confirmed that these AEs can be anticyclonic coherent structures down to the bottom (~3000 m). Additional complexity arises, however, from recent observations showing that this vertical coherence down to the bottom is not permanent. AEs detached from the Algerian slope then drift northward along the Sardinian one. Before reaching ~40oN, AEs detach from the Sardinian slope and propagate in the open basin. Some AEs come back eventually close to the Algerian slope, where they interact with their parent current.
- Peter Saundry. 2011. Seas of the world. Topic ed. C.Michael Hogan. Ed-in-chief Cutler J.Cleveland.
- I. Puillat, I. Taupier-Letage, and C. Millot. Algerian Eddies lifetime can near 3 years. Journal of Marine Systems, 31:245–259, 2002.