Horizontal convection: the role of turbulence

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Intellectual Merit: Horizontal convection is the generic designation for the circulation resulting from differential heating along one horizontal boundary of a fluid. It is a key feature of the ocean's Meridional Overturning Circulation. The full problem of the Meridional Overturning Circualtion is complex and difficult, involving thermal, haline, and mechanical forcing. Understanding the simpler problem of (single-component) horizontal convection is an important step in attacking the full problem. Mixing is critically important in producing a pathway for cold water to be modified and return to the surface. Molecular processes are far too puny to carry out this role. The role of turbulence in horizontal convection is hence crucial.The laboratory and numerical experiments on horizontal convection will address five hypotheses:1. Scaling for the boundary-layer thicknesses of previous work is correct. 2. Dissipation is highly variable in space. 3. The boundary between steady and unsteady regimes is a function of aspect ratio, dimensionality, and rotation. 4. Small-scale variability of the boundary forcing should shut down large-scale convection. 5. Combined buoyancy and mechanical forcing changes the regime diagram.Broader Impacts: The investigators will engage in educational activities at multiple levels. The environmental fluid dynamics laboratory, in which the lead investigator works, has a strong track record in undergraduate mentoring. They will recruit an undergraduate and will work with UCSD's McNair Program and/or the Summer Training Academy for Research in the Sciences (STARS) program, both of which target students are from groups traditionally underrepresented in the sciences. The research will involve two graduate students. Reaching pre-college students will contribute to the professional development of high school teachers in the San Diego Unified School District. In partnership with the NSF-funded Center for Ocean Science Education Excellence/California they will sponsor a one-day workshop for approximately 25 Earth sciences teachers. The investigators will contribute to the Wiki page of the CFD code chosen for this work. These posts will broadly disseminate key results of NSF-funded work in a venue that is accessed by the larger CFD community, thus enhancing scientific and technological understanding. The results of the project have applications in industry and to environmental sustainability, as well as in related fields of science, in particular limnology and climate science. The experiments carried out here are relevant to natural ventilation of buildings. Improved understanding of the fluid mechanics of natural ventilation, an anticipated outcome of the project, can inform critical energy conservation efforts that may ultimately benefit society economically, environmentally and politically.