A PROPOSED FLUX CONSTRAINT FOR SALT FINGERS IN SHEAR

Towed ocean microstructure observations reveal that the temperature Co x number depends inversely on interface temperature-gradient (T) over bar(z) in the fingering-favorable thermohaline staircase east of Barba dos. This implies fluxes independent of interface gradients. These con clusions are contrary to theoretical expectations from a finger Froude number stability criterion, \del\/N < 1.0: (i) Cox numbers independen t of temperature gradient, and (ii) fluxes varying linearly with tempe rature gradient. We propose a hybrid wave/finger Froude number stabili ty criterion, \(u(z) - w(x))(w(y) - v(z))\N-2 less than or equal to 1. 0 which reduces to U-z\del w\/N-2 less than or equal to 1.0 for salt s heets (partial derivative/partial derivative x = 0,\del w\ = w(y)) ali gned with background (internal-wave) shear U-z. The sheet criterion re produces the observed behavior. For weak but nonzero background shears , 0.1 < U-z/N < 1.0, this constraint implies higher fluxes than unshea red square-planform fingers constrained by a finger Froude number \w(x )w(y)\/N-2 < 1.0.