Layering in Atmospheres, Oceans and Plasmas

Coordinators: Patrick H. Diamond, Pascale Garaud, David W. Hughes, and Bruce Sutherland

Scientific Advisors: Mary-Louise Timmermans and Bill Young

Fluid and plasma turbulence often manifests the spontaneous formation of ‘staircases’ or layered structures – arrays of finite homogenized domains separated by sharp gradients that act as transport barriers. This is surprising, because normally one expects turbulent mixing to cause homogenization. Across a wide range of physical systems layering exerts a critical control on dynamics and transport:

  • For staircases in density stratified fluids, turbulence forms layers by still poorly understood ‘self-sharpening effects’ in density mixing. This is of great importance to a wide range of atmosphere, ocean, and engineering applications.
  • For potential vorticity (PV) staircases in rotating geophysical fluid systems, sequences of PV jumps form that are associated with sharp jets and act as barriers to material transport.
  • Staircases in magnetized plasmas constitute an important new type of secondary pattern. They resemble a lattice of internal transport barriers and their scales define the effective mixing or transport scale of the system. The latter is a major issue in fusion science.
  • For layering in doubly diffusive convection that occurs in oceans, planetary atmospheres, and stellar interiors, the mechanisms leading to long-lived density staircases remain unsettled, especially in light of inconsistencies between simulations and observations.

This program will foster interdisciplinary interaction among plasma physicists, oceanographers, geophysical and astrophysical fluid dynamicists, soft-condensed-matter physicists and applied mathematicians—all of whom confront problems in layering. The aims are cross-disciplinary fertilization, nucleation of new collaborations, and progress toward a collective understanding of what physics is fundamental to the occurrence of layering.