The instability of stratified flows at large Richardson numbers.
In contrast to conventional expectations based on the stability of steady shear flows, elementary time-periodic stratified flows that are unstable at arbitrarily large Richardson numbers are presented here. The fundamental instability is a parametric one with twice the period of the basic state. This instability spontaneously generates local shears on buoyancy time scales near a specific angle of inclination that saturates into a localized regime of strong mixing with density overturning. We speculate that such instabilities may contribute significantly to the step-like microstructure often observed in buoyancy measurements in the ocean.
Madja
A J
AJ
Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA.
Shefter
M
M