Schedule May 21, 2018
Oceanic boundary layer frontogenesis & wave interactions
Jim McWilliams (UCLA)

Oceanic submesoscale currents near the surface primarily have patterns of lines or streaks with widths of 10-1000 m. The lines are made visible by high concentrations of buoyant surface materials (much of which is biogenic scum) that are pushed together where horizontal currents converge and feed into downward current sheets, leaving the surfactants behind. These lines are created by the process of frontogenesis where horizontal differences in density are compacted into smaller cross-front transition zones, with the associated current patterns following along. Two primary points are made in this talk: (1) the currents that cause the frontogenesis are created by the combined effects of the density differences, Coriolis force, and vertical momentum mixing associated with turbulence in the surface boundary layer; (2) the rate of frontogenesis is equivalent to the rate of frontogenesis once the front is strong enough. Statement (2) is not the common view of meteorological weather fronts where the frontogenesis rate is usually attributed to the strain rate of the winds, which can be true for weak and moderate fronts, but not for strong ones. The details of frontogenesis at the ocean surface are also influenced by surface gravity waves.

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