The role of molecular diffusion in the deepening of the mixed layer

Yign Noh, Harindra J.S. Fernando

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


Turbulent mixing across heat-stratified density interfaces was studied in the laboratory using oscillating-grid generated turbulence. The aim was to study the transition between the entrainment regimes dominated by interfacial wave-breaking and molecular diffusion, and to study the characteristics of the latter. It was observed that, above a critical Richardson number Ric, which depends on the Peclet number Pe, the mixing due to wave breaking disappears and that Ric ∼ Pe-n, where the mean value of the exponent n is approximately 1 2. Above Ric, the entrainment is molecular-diffusion dominated and takes place through a sequence of events: the buoyancy gradient of the initially sharp density interface is weakened by molecular diffusion until the mixed-layer eddies can engulf a portion of the interfacial layer wherefore the interface sharpens again. Thus, the entrainment events are recurrent with a rate-controlling diffusion stage between them. An entrainment law of the form E ∼ Ri-2Pe-2, where E is the entrainment coefficient and Ri is the Richardson number, is suggested for the diffusion-dominated entrainment regime.

Original languageEnglish
Pages (from-to)187-215
Number of pages29
JournalDynamics of Atmospheres and Oceans
Issue number2-3
Publication statusPublished - Jan 1993
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Geology
  • Computers in Earth Sciences
  • Atmospheric Science


Dive into the research topics of 'The role of molecular diffusion in the deepening of the mixed layer'. Together they form a unique fingerprint.

Cite this