Staircase formation in unstably stratified double diffusive finger convection

TL;DR

This study experimentally investigates staircase formation in double diffusive convection with stabilizing temperature and destabilizing ion concentration gradients, revealing new insights into finger dynamics and transport mechanisms.

Contribution

It provides the first experimental evidence of staircase formation under unstable density stratification and challenges existing theories on their formation mechanisms.

Findings

Staircases form even with unstable density stratification.

Existing theories do not fully explain the observed staircase formation.

Ion transport differs between finger segments and entire cells.

Abstract

Double diffusive staircases are investigated experimentally in a fluid layer with a stabilizing temperature gradient and a destabilizing gradient of ion concentration. Gradients of temperature and ion concentration are maintained in a steady state within an electrochemical system. Staircases are observed even if the density stratification is unstable. None of the previously proposed mechanisms for staircase formation can be recognized in the experiments. Ion transport through fingers which are part of a staircase is not the same as transport through fingers extending through the entire cell. Fingers cease to exist if the diffusive heat transport between neighboring fingers is insufficient.