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.
|Original language||English (US)|
|Number of pages||4|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Jul 7 1998|
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