Separation of a midlevel density current from the bottom of a continental slope

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FONTE

The National Academy of Sciences

RESUMO

The high-salinity water flowing out of the Mediterranean Sea descends to mid depths in the density-stratified ocean, continues as a narrow jet along the Iberian continental slope, and intermittently detaches large-scale eddies (called “Meddies”). This process is important because it maintains the relatively high mean salinity of a major water mass (the “Mediterranean Intermediate Water”) in the North Atlantic. Our simplified model of this jet consists of a moving layer with intermediate density ρ2 sandwiched between motionless layers of density ρ1 < ρ2 and ρ3 > ρ2. The inshore (anticyclonic) portion of the midlevel jet (in the “ρ2-water”) rests on an inclined bottom (the continental slope), whereas the (cyclonic) offshore portion rests on the density interface of the stagnant deep (ρ3) layer. An inviscid, steady, and finite-amplitude longwave theory is used to show that if the cross-stream topographic slope increases gradually in the downstream direction, then the “ρ2-jet” is deflected off the bottom slope and onto the upper density interface of the ρ3 layer. The computed magnitude of this separation effect is such as to produce an essentially free jet which is removed from the stabilizing influence of the continental topography. It is therefore conjectured that time-dependent effects (baroclinic instability) will produce further amplification, causing an eddy to detach seaward from the branch of the jet remaining on the slope.

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