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The Alboran Sea mesoscale in a long term high resolution simulation: Statistical analysis

Peliz A, Boutov D, Teles-Machado A
Ocean Modelling 72 (2013) 3252, https://doi.org/10.1016/j.ocemod.2013.07.002

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Abstract

We analyze the Alboran Sea mesoscale variability in a 2-decade high resolution (2 km) simulation. The circulation modes and eddies are described from a statistical perspective. The double-gyre quasi-steady state is confirmed as the most common circulation mode in the Alboran Sea (48% of the time), followed by single-gyre mode in about 24% of the situations. These persistent modes are compared in terms of structure, frequency of occurrence and seasonality, energetics, and their links to inflow variability and wind forcing. The double-gyre state is the most stable situation with higher kinetic and potential energy and lower eddy kinetic energy and seems to be limited by a critical value of the Rossby radius (~12 km). The transitions between the quasi-steady states are studied and typified with a particular focus on the Western Alboran Gyre migration which stands out as the major contributor for flow transitions. A typical sequence of flow types and transients is proposed: The double-gyre is usually canceled after a migration event occurring in late summer or autumn. The Western Alboran Gyre is not immediately replaced by a new born anticyclone. Instead, there is a cycle of migration-merging events with the Eastern Alboran Gyre which eventually force the latter to move westward and form a single-gyre situation. The generation of a second Eastern Alboran Gyre in spring-early summer sets the beginning of a new double-gyre stable period. An analysis of coherent mesoscale eddies is conducted and their statistics, sites and processes of generation are described. Cyclones (anticyclones) mean radius are in the range of ~12 km (~15 km), they are much more frequent in winter time and cyclones significantly outnumber the anticyclones. The link of mesoscale processes and transients (in particular of migrations) with the inflow is analyzed, and no clear relationship of transient events with inflow magnitude is disclosed. On the other hand, the large majority of transitions (specially migrations) are associated with a clear shift of the angle and latitude of the Atlantic Jet to the south. The stratification and wind variability are also important suggesting a significant role of eddy dynamics and intrinsic variability in determining the stable modes and transitions. Despite the seasonality of the flow types sequence, there are periods of long stability with the double-gyre blocking situations resisting the winter periods. The time variability is analyzed and compared with observations.