Dynamics of Langmuir Circulation in Oceanic Surface Layers.
Abstract
This work investigates whether large-scale coherent vortex structures driven by wave-current interaction (Langmuir circulation) are responsible for maintaining the oceanic mixed layer. Langmuir circulations dominate the near-surface vertical transport of momentum and density when the characteristic scale for forcing (defined as the Craik-Leibovich instability parameter gamma sub CLS) is stronger than the characteristic scale for diffusive decay gamma sub diff. Since the wave-current forcing is concentrated near the surface both terms depend on the cell geometry. Cells with long wavelengths penetrate more deeply into the water column. These cells grow more slowly than the fastest growing mode for most cases, but always dominate the solution in the absence of Coriolis forces. In the presence of Coriolis forces, the horizontal wavelength and thus the depth of penetration are limited. When a cell geometry is found such that gamma sub CLS >> gamma sub diff. the current profile produced by small- scale diffusion is unstable to Langmuir cells and the cells replace small-scale diffusion as the dominant vertical transport mechanism for momentum and density. The perturbation crosscell shear is predicted to scale as gamma sub CLS. Such a scaling is observed during two field experiments. (MM)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1994
- Accession Number
- ADA296834
Entities
People
- Anand Gnanadesikan
Organizations
- Woods Hole Oceanographic Institution