Weekly Seminar: Fall 2014
Speaker: Prof. Tobias Kukulka (University of Delaware)
Title: "Rapid Mixed Layer Deepening by the Combination of Langmuir and Shear Instabilities: A Case Study"
Date: Friday, September 12, 2014
Time: 11:00 a.m.
Location: Gilman Hall 132
Langmuir circulation (LC) is a turbulent upper-ocean process driven by wind and surface waves that contributes significantly to the transport of momentum, heat, and mass in the oceanic surface layer. We perform a direct comparison of large-eddy simulations and observations of the upper-ocean response to a wind event with rapid mixed layer deepening. The evolution of simulated crosswind velocity variance and spatial scales, as well as mixed layer deepening, is only consistent with observations if LC effects are included in the model. Based on an analysis of these validated simulations, the differences in mixing between purely shear-driven turbulence and turbulence with LC are identified. LC transports horizontal momentum efficiently downward leading to an along-wind velocity jet below LC downwelling regions at the base of the mixed layer. Locally enhanced shear instabilities as a result of this jet efficiently erode the thermocline. In turn, enhanced breaking internal waves inject cold deep water into the mixed layer, where LC currents transport temperature perturbation advectively. Thus, LC and locally generated shear instabilities work intimately together to facilitate strongly the mixed layer deepening process.
Tobias Kukulka studied physics at Freie Universität Berlin in Germany before earning a master of science degree in environmental science and engineering from Oregon Health and Science University. During his doctoral studies at the University of Rhode Island, he researched the effect of breaking waves on wind and ocean surface waves and finished his Ph.D. in 2006. He worked as a postdoctoral scholar at Woods Hole Oceanographic Institution and joined the University of Delaware in 2010. His interests center on air-sea interactions, physical oceanography, upper ocean dynamics, surface waves, large eddy simulations, ocean modeling, high performance computing.