Baroclinic instability of buoyancy-driven coastal density currents

摘要: Coastal density currents induced by buoyancy supply along an upper coast are studied in a three-dimensional numerical model. Scaling analysis of the governing equations reveals that when vertical eddy diffusivity is small, horizontal Ekman number Eh = Ahƒ/(g'Qe)2/3 crucial parameter determining structures current, where Ah viscosity, Qe discharge rate per unit length coast, g' reduced gravity constant, and ƒ Coriolis parameter. Based on experiments with varied as external parameters, critical (Ehc) found between 0.354 0.566. The current develops unstably below this value. In cases < Ehc, excessive accumulation fresh water causes sudden changes near which eventually breaks down quasi-steady balance triggers small-scale disturbances long-shore direction. large-scale unstable waves these have scales order 100 km e-folding time several days. Study energetics revealed grow via baroclinic process, they develop into finite-amplitude stage, energy transfer from field to mean accelerates induces oppositely flowing flow offshore. These flows important detachment process fully developed eddies.