Mesoscale Dynamics and Vertical Motion in the Alborán Sea

Abstract

The inflow of Atlantic water through the strait of Gilbraltar usually exhibits a stationary wavelike pattern in the Alborán sea. We use an objective analysis technique for quantitative scale separation to investigate the interaction of scales in the region. The large scale is clearly dominated by an anticyclonic gyre. Smaller scale analysis shows the existence of several mesoscale cyclonic eddies along the northern boundary of the western Alborán sea anticyclonic gyre. The relationship between the large-scale/mesoscale variability and the induced ageostrophic vertical motion is established using the Q vector formulation. We find that on the macroscale, upward motion occurs upstream of the anticyclonic gyre (upstream of a wave crest) while downward motion takes place downstream (upstream of a trough). We also show that the vertical motion associated with the mesoscale eddies is an order of magnitude higher than the large-scale vertical motion. These patterns of large-scale and mesoscale vertical motions are confirmed by an extensive sensitivity analysis and by an independent estimate of the large-scale vertical velocity.