Boundary Layer Meteorology Lecture 17: Oceanic and Lacustrine Boundary Layers

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Boundary Layer Meteorology Lecture 17Oceanic
and Lacustrine Boundary Layers

• Similarities and differences between Atmospheric
  and Oceanic/Lacustrine Boundary Conditions
• Ocean Waves
• Langmuir circulations

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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.

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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

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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.

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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
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Langmuir Circulations

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

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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

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Langmuir Circulations

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

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Incorporating Waves and Langmuir circulations in
models

• Noh et al. 2004
• McWilliams et al., 1997