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

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.

[1]  A. S. Roman,et al.  The Western Alboran Gyre helps ventilate the Western Mediterranean Deep Water through Gibraltar , 2012 .

[2]  P. Soares,et al.  The Gulf of Cadiz-Alboran Sea sub-basin: Model setup, exchange and seasonal variability , 2013 .

[3]  Joaquín Tintoré,et al.  Circulation in the Alboran Sea as Determined by Quasi-Synoptic Hydrographic Observations. Part I: Three-Dimensional Structure of the Two Anticyclonic Gyres , 1996 .

[4]  C. Millot.  Circulation in the Western Mediterranean Sea , 1999 .

[5]  Tommy D. Dickey,et al.  A Vector Geometry–Based Eddy Detection Algorithm and Its Application to a High-Resolution Numerical Model Product and High-Frequency Radar Surface Velocities in the Southern California Bight , 2010 .

[6]  Paul E. La Violette,et al.  The Advection of Submesoscale Thermal Features in the Alboran Sea Gyre , 1984 .

[7]  Álvaro Viúdez.  An Explanation for the Curvature of the Atlantic Jet past the Strait of Gibraltar , 1997 .

[8]  F. Hernandez,et al.  A mean dynamic topography computed over the world ocean from altimetry, in situ measurements, and a geoid model , 2004 .

[9]  J. Soto-Navarro,et al.  Estimation of the Atlantic inflow through the Strait of Gibraltar from climatological and in situ data , 2010 .

[10]  Anny Cazenave,et al.  Sea level variations in the Mediterranean Sea and Black Sea from satellite altimetry and tide gauges , 2002 .

[11]  D. Chelton,et al.  Geographical Variability of the First Baroclinic Rossby Radius of Deformation , 1998 .

[12]  Alexander F. Shchepetkin,et al.  The regional oceanic modeling system (ROMS): a split-explicit, free-surface, topography-following-coordinate oceanic model , 2005 .

[13]  Michel Crépon,et al.  A Strait Outflow Circulation Process Study: The Case of the Alboran Sea , 1996 .

[14]  Pedro M. A. Miranda,et al.  WRF high resolution dynamical downscaling of ERA-Interim for Portugal , 2012, Climate Dynamics.

[15]  A. Carillo,et al.  Three‐layer view of transports and hydraulics in the Strait of Gibraltar: A three‐dimensional model study , 2007 .

[16]  P. Marchesiello,et al.  Filament generation off the Strait of Gibraltar in response to Gap winds , 2009 .

[17]  M. Vargas,et al.  Low-frequency variability of the exchanged flows through the Strait of Gibraltar during CANIGO , 2002 .

[18]  J. Vargas,et al.  About the seasonal variability of the Alboran Sea circulation , 2002 .

[19]  Joaquín Tintoré,et al.  A study of an intense density front in the eastern Alboran Sea: the Almeria-Oran front , 1988 .

[20]  Joaquín Tintoré,et al.  Surface circulation in the Alborán Sea (western Mediterranean) inferred from remotely sensed data , 2012 .

[21]  M. Vargas,et al.  Evolution of the Alboran Sea hydrographic structures during July 1993 , 1998 .

[22]  P. Vélez-Belchí,et al.  Observation of a western Alborán gyre migration event , 2005 .

[23]  X. Capet,et al.  Submesoscale dynamics in tropical instability waves , 2011 .

[24]  C. Garrett,et al.  A simple criterion for gyre formation by the surface outflow from a strait, with application to the Alboran Sea , 1989 .

[25]  P. L. Violette,et al.  Variations in the structure of the anticyclonic gyres found in the Alboran Sea , 1990 .

[26]  P. Marsaleix,et al.  Comparison of Ocean Dynamics with a Regional Circulation Model and Improved Altimetry in the North-Western Mediterranean , 2008 .

[27]  A. Pascual,et al.  In situ and satellite observations of the eastward migration of the Western Alboran Sea Gyre , 2006 .

[28]  A. Miller,et al.  Laboratory simulation of the gyre in the Alboran Sea , 1979 .

[29]  Jean-Michel Pinot,et al.  On the upper layer circulation in the Alboran Sea , 1998 .

[30]  D. Nof,et al.  The Establishment of the Tsugaru and the Alboran Gyres , 1999 .

[31]  A. Pascual,et al.  A Mean Dynamic Topography of the Mediterranean Sea computed from altimetric data, in-situ measurements and a general circulation model , 2007 .

[32]  Yuping Guan,et al.  Three‐dimensional oceanic eddy analysis in the Southern California Bight from a numerical product , 2012 .