Berkeley Fluids Seminar

Monday, October 9, 2017

3110, Etcheverry Hall, 12:00-13:00

Prof. Sutanu Sarkar (UC San Diego)

Submesoscale vortices and gravity currents at density fronts

Abstract: Density fronts form between the saline ocean and fresh water from river input. These frontal regions modulate the sea surface temperature and thereby air-sea interaction through submesoscale (horizontal scale less than a few km) features and associated vertical fluxes. We use LES to examine the nonlinear evolution of flow instabilities and turbulence at fronts that are initially in geostrophic balance. Fronts with strong horizontal gradient develop a cross-front circulation that strengthens and eventually leads to a surface gravity current. This process may help understand recent shipboard observations in the Bay of Bengal that have identified gravitycurrent features at fronts that are unusually strong and thin. When the horizontal density gradient is moderate, the flow exhibits symmetric instability (slantwise convection), baroclinic instability as well as mixed modes. Vortex filaments form and are found to break down into three-dimensional turbulence as well as to organize and form submesoscale vortices. We will discuss the variation of flow properties as a function of the upper-ocean vertical stratification in both cases: strong and moderate horizontal density gradient.

Bio: Sutanu Sarkar received his Ph.D. from the Mechanical Aerospace Engineering Department at Cornell University in 1988. He spent the following years until 1992 as a staff scientist in the Institute for Computer Applications in Science and Engineering (ICASE) at NASA Langley Research Center. He has been with the MAE faculty since 1993. His honors include a NASA group achievement award (1994), Friedrich Wilhelm Bessel Research Prize (2001) from the Humboldt Foundation, Fellow of the American Physical Society (2006), Associate Fellow of the American Institute of Aeronautics and Astronautics (2010) and Fellow of the American Society of Mechanical Engineers (2010).

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Acknowledgments

Prof. Graham Fleming (Vice Chancellor for Research, UC Berkeley)

Prof. Eliot Quataert on behalf of The Theoretical Astrophysics Center and the Astronomy Department (UC Berkeley)

Prof. Philip S. Marcus on behalf of the Mechanical Engineering Department (UC Berkeley)

Prof. Michael Manga (Earth and Planetary Science, UC Berkeley)

Prof. Evan Variano (Civil and Environmental Engineering, UC Berkeley)