Topographically induced circulation patterns and mixing over Condor seamount

Abstract

Analysis of mean and oscillatory circulation patterns over Condor seamount, situated near the central group of the Azores islands, was performed. During 1.5 years of observations, at least half of the time an anticyclonic cap was established over the summit. The vortex was characterised by a strong asymmetry: it was shifted to the south of the summit and strongly stretched along the gentle eastern and western slopes of the seamount.Three mechanisms are suggested to generate the anticyclonic cap: impinging mean flow, tidal rectification, and vertical turbulent density fluxes. Our estimates suggest that tidal rectification alone can explain the formation of the observed anticyclonic cap, but the character of temporal variation of its intensity gives evidence that impinging flow also plays an important role in the cap dynamics. Conditions for stability of the anticyclonic cap are found to be principally different depending on the impinging flow being unidirectional or dominated by synoptic oscillations. For a unidirectional impinging flow, in close accordance with the theory, anticyclonic cap was readily formed over the top of the seamount. The cap was stable, except for the events of the cap shedding when the impinging flow accelerated above a critical level. When the impinging flow varied its direction, dominated by topographic Rossby waves, the anticyclonic cap was absent or its intensity got significantly reduced. Vertical turbulent density flux was of secondary importance for formation of the anticyclonic cap over the summit.