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Project details: ShIC

Acronym: ShIC
Title: Quantification of shear-induced convection and bottom boundary layer mixing in natural waters
Duration: 01.10.2006 - 15.10.2010
Project manager: PD Dr. Lars Umlauf
Funding: DFG
Focus: Transport and transformation processes
Department: Physical Oceanography and Instrumentation

Andreas Lorke (University of Konstanz, Germany)


Alfred Wüest (EAWAG, Switzerland)


Johannes Becherer


Schematic view of shear-induced BBL convection

In a joint project with the University of Konstanz (Germany) and the EAWAG (Switzerland), we investigate the dynamics of gravitationally unstable bottom boundary layers in lakes of different sizes, and in the Baltic Sea. Such unstable bottom boundary layers occur if, as illustrated in the figure, internal wave motions (here due to internal seiching) move stratified fluid up the slope. The near-bottom shear created by these motions favours the advection of dense fluid above less dense fluid. Under these circumstances, convection forms an additional energy source for turbulence that may substantially modify turbulence and mixing in the bottom boundary layer (Lorke et al. 2008).Conversely, if water is moved down the slope, the near-bottom shear has a tendency for the creation of stable stratification. This process is similar to the periodic creation of unstable and stable stratification due to 'tidal straining' in regions of fresh-water influence (ROFIs) on the continental shelf.

If the scales are large enough, the boundary layer dynamics is affected by rotation. The physics of this process will be studied with data from several cruises conducted in 2008-2010 in the Baltic Sea, and with the help of an extensive modeling program.