Abstract

Fingering convection occurs when the density of a fluid is affected bytwo scalars: a slowly diffusing one, which, if acting alone, wouldcreate a top-heavy stratification, and a fast-diffusing one, arrangedin such a way as to produce an overall bottom-heavy stratification.The different diffusivities of the two buoyancy-changing scalars leadsto a well-understood instability of the motionless state, which resultsin the formation of small buoyancy-carrying structures (known as saltfingers) moving in a fluid which, at scales larger than that of thosesmall structures, maintains a bottom-heavy stratification, with aconstant vertical density gradient.  When this kind of convection issufficiently vigorous, the large-scale density profile may undergo asubsequent instability which disrupts the constancy of its verticalgradient, and leads to a layered density profile where well-mixedlayers are alternated to layers where density assumes a steep verticalgradient.  Several mechanisms have been proposed in order to explainthe layer-forming instability. Some emphasize the peculiarities of thedoubly-diffusive mechanisms that continuously creates small-scalesbuoyancy anomalies, others mimic long-standing models of layerformation in mechanically stirred, stably-stratified fluids. Finally,a recent work that subsumes most of these (apparently?) distinctmechanisms within a single framework will be discussed.