Multiple states and transport properties of double-diffusive convection turbulence

Yantao Yang*, Wenyuan Chen, Roberto Verzicco, Detlef Lohse

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

When fluid stratification is induced by the vertical gradients of two scalars with different diffusivities, double-diffusive convection (DDC) may occur and play a crucial role in mixing. Such a process exists in many natural and engineering environments. Especially in the ocean, DDC is omnipresent since the seawater density is affected by temperature and salinity. The most intriguing phenomenon caused by DDC is the thermohaline staircase, i.e., a stack of alternating well-mixed convection layers and sharp interfaces with very large gradients in both temperature and salinity. Here we investigate DDC and thermohaline staircases in the salt finger regime, which happens when warm saltier water lies above cold fresher water and is commonly observed in the (sub)tropic regions. By conducting direct numerical simulations over a large range of parameters, we reveal that multiple equilibrium states exist in fingering DDC and staircases even for the same control parameters. Different states can be established from different initial scalar distributions or different evolution histories of the flow parameters. Hysteresis appears during the transition from a staircase to a single salt finger interface. For the same local density ratio, salt finger interfaces in the single-layer state generate very different fluxes compared to those within staircases. However, the salinity flux for all salt finger interfaces follows the same dependence on the salinity Rayleigh number of the layer and can be described by an effective power law scaling. Our findings have direct applications to oceanic thermohaline staircases.

Original languageEnglish
Pages (from-to)14676-14681
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number26
DOIs
Publication statusPublished - 30 Jun 2020

Keywords

  • double-diffusive convection
  • thermohaline staircase
  • turbulence

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