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Boundary Layer Meteorology Lecture 17: Oceanic and Lacustrine Boundary Layers

Boundary Layer Meteorology Lecture 17: Oceanic and Lacustrine Boundary Layers. Similarities and differences between Atmospheric and Oceanic/Lacustrine Boundary Conditions Ocean Waves Langmuir circulations. Similarities between Oceanic and Atmospheric Boundary Layers.

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Boundary Layer Meteorology Lecture 17: Oceanic and Lacustrine Boundary Layers

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  1. Boundary Layer Meteorology Lecture 17:Oceanic and Lacustrine Boundary Layers • Similarities and differences between Atmospheric and Oceanic/Lacustrine Boundary Conditions • Ocean Waves • Langmuir circulations

  2. Similarities between Oceanic and Atmospheric Boundary Layers • M-O theory applied to both surface layers • Mixed layer models used in a very similar way • Etc.

  3. Differences between Oceanic and Atmospheric Boundary Layers • Presence of Salinity (but note analog of ocean density, virtual temperature) • Boundary at top, not bottom • Free-slip, versus no-slip boundary • Wave-induced measurement difficulties (and general lack of data, though this will improve in the next few years, due to migrating remote buoys). • Wave-induced TKE generation • Langmuir circulations

  4. Ocean Waves • Observations; wave dispersion relations for shallow and deep water • Big source of turbulent kinetic energy in top 5 meters • Incorporation of atmospheric gases, momentum(?) due to wave breaking, bubbles, spray.

  5. Langmuir Circulations Photo Credit: S.A. Thorpe “Discovering the causes of Lc and quantifying and identifying its effects has been difficult. Studying the associated dynamical processes involves some of the most intellectually demanding problems of theoretical and observational fluid dynamics, several of which remain intractable.” -S.A. Thorpe

  6. Langmuir Circulations • Interaction of stokes drift, surface shear current yields vortices (images from Thorpe, 2004, Ann. Rev. Fluid Mech., 36(1):55) • Conceptual diagram:

  7. Langmuir Circulations • New observations have complicated our picture of these circulations. • Rolls are now seen to be time-varying, twisted, irregularly spaced, and frequently combining and separating

  8. Langmuir Circulations • Previously thought to be a laminar process that confined materials, resisted dispersion, now seen as a turbulent process that aids dispersion.

  9. Incorporating Waves and Langmuir circulations in models • Noh et al. 2004 • McWilliams et al., 1997

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